International Centre for Underwater Archaeology in Zadar

CONSERVATION OF UNDERWATER ARCHAEOLOGICAL FINDS

MANUAL II. edition

Zadar, 2014.

CONSERVATION OF UNDERWATER ARCHAEOLOGICAL FINDS MANUAL This Manual is intended for use at Advanced Course on the Restoration and Conservation of Underwater Archaeological Finds CONTENTS

II. edition, Zadar, 2014.

Editor: Bekiü Luka I. Underwater Cultural Heritage and the UNESCO Convention 7 Authors: Bekiü Luka Bekiü Luka ûurkoviü Martina Jeliü Anita II. Guidelines, Ethics and the Methodology of Conservation - Restoration Work 14 Joziü Antonija Martinoviü Ivo Mustaþek Mladen Mustaþek Mladen III. Causes of the Decay of Archaeological Material 17 Perin Tanja Pešiü Mladen Mustaþek Mladen IV. The Conservation and Restoration of Ceramics and Pottery 26 Expert advisor: Tran Quoc Khoï, Atelier Régional de Conservation ARC-Nucléart CEA-Grenoble, France ûurkoviü Martina

Translation to English: Ferenþiü Neven V. The Conservation and Restoration of Glass 39 ûurkoviü Martina Graphic design: Šimiþiü Marina VI. The Conservation and Restoration of Metal Finds 47 Press: Futuro I. S., Zadar Joziü Antonija VII. Organic Material 60 Edition: 200 Jeliü Anita

Publisher: International Centre for Underwater Archaeology in Zadar VIII. The Conservation and Restoration of Stone Finds 76 B.Petranoviüa 1, HR-2300 Zadar, Croatia Martinoviü Ivo

IX. The Handling, Packing, Transport and Storage of Underwater 84 Archaeological Finds

Perin Tanja, Jeliü Anita

X. In situ Protection of Underwater Cultural Heritage 97 Pešiü Mladen This Manual was initially created with the support of the UNESCO Venice Office. BIBLIOGRAPHY 108

INTERNET SOURCES 113

Not for sale CIP-Katalogizacija u publikaciji Znanstvena knjižnica Zadar UDK 902.034(497.5)(035) CONSERVATION of underwater archaeological finds : manual / ; editor Luka Bekiü ; translati- on to English Neven Ferenþiü>. - 2nd ed. - Zadar : International Centre for Underwater Archaeology in Zadar, 2014. - 116 str. : ilustr. (pretežno u bojama) ; 31 cm Bibliografija.

ISBN 978-953-56855-1-7

1. Bekiü, Luka 140801029

Bekiü L.: Underwater Cultural Heritage and the UNESCO Convention 7 I. Underwater Cultural Heritage and the UNESCO Convention

Luka Bekiü me. Sunken human formations (features) beca- [email protected] me increasingly accessible. And so people, irre- spective of the desires that motivated them, fo- und it easier to access the environment of these sunken formations and act upon them. A great INTRODUCTION deal of this human activity has led to the excavation, relocation, damaging and removal of Sunken ships, settlements and various other many underwater finds, whereby the sunken hidden and valuable finds in the depths of the formations have lost their characteristic attribu- sea have always stirred the interest of people tes and disappeared - a fact that has evoked and their desire to reach them. The motivations concern. to access these sunken traces of human pre- sence have been diverse. On the one hand the- re is the ever - present factor of human curiosity, desire for knowledge and an understanding of events around us and over time and, on the ot- her, a desire to gain wealth, including valuable and rare material property.

Figure 2. Geldermalsen shipwrek auction catalogue (www.china.org.cn)

Particularly detrimental were the many activities in which sunken objects were collected solely for their commercial value - a concept that gave no Figure 1. Typical representation of a myth of consideration whatsoever to the essence of the underwater treasures (www.etsy.com) find site and its future.There are many examples of various unscrupulous enterprises (treasure The traces of human activity that have disappe- hunters) that, under sundry arrangements, ared under the waves were once sundered from extracted (salvaged) numerous valuable finds, in our onshore existence by the significant obstac- the process destroying all the traces and data le of underwater depth. With time and human that might have been collected. progress this obstacle has largely been overco-

Conservation of Underwater Archaeological Finds - MANUAL 8 Bekiü L.: Underwater Cultural Heritage and the UNESCO Convention 9

The wreck of the Tek Sing was looted in the So- scientific approach to the research of THE PRINCIPLES uth China Sea - over 300 thousand pieces of underwater heritage, which encourages a res- The first principle is the obligation to valuable Chinese porcelain were salvaged in ponsible attitude towards underwater cultural heritage. These research endeavours, crowned protect cultural heritage for the benefit 1999 and later sold at auction. A British operator by comprehensive publication of the results of of humanity. Accordingly, states parti- salvaged over 126 gold bars and 160 thousand research and the exhibition of finds to the wider es to the Convention (signatories) porcelain items from the wreck of the Dutch ves- public have raised the level of awareness of the should protect underwater heritage. sel Geldermalsen near Nanjing, later sold at au- real value of this heritage. Each state implements this protection ction. Certainly the richest shipwreck is the Spa- in accordance with its capabilities, nish galleon Nuestra Señora de Atocha found Estimates put the number of sunken vessels in and if it is not able to undertake rese- off the Florida coast and ransacked by a private the world's seas at over three million. A great arch of an archaeological site, it is number of once populated settlements are also enough that it provides appropriate company in a most destructive fashion to extract now underwater, as are many other diverse and protection of the site. The Convention its cargo of gold and other objects, subsequently Figure 5. Uluburun wreck, reconstruction at Bodrum Museum encourages scientific research of sites not easily discernable traces of habitation and (en.wikipedia.org) sold through various channels. The list of looted activity. That truly valuable cultural heritage is to and public access. shipwrecks is a long one and still growing. be found underwater is more than evident. 1996 ICOMOS Charter on the Pro- tection and Management of the The past few decades have seen numerous initi- Underwater Cultural Heritage came atives at the national level, and a great many as a major step forward. It was on laws and regulations have been adopted gover- the basis of this charter that the ning the methods whereby underwater heritage UNESCO Convention on the Pro- is protected. These rules were, however, diver- tection of the Underwater Cultural se, and, as a result, cooperation at the internati- Heritage was finally adopted in onal level was launched with the aim of harmoni- 2001. This was followed by its ratifi- sing and broadening the efforts targeted to pro- cation in some forty countries, ma- tection to as many countries as possible. king this to date the most important Following various initiatives the adoption of the international achievement in the legal protection of underwater heri- tage. This convention defines underwater heritage as all traces of Figure 6. The bow of the Titanic shipwreck (wavesnewsletter.com) human activity that possess a cultu- ral, historic or archaeological significance and PRESERVATION that were sunk at least 100 years ago. This has set the legal grounds for the preservation of this The Convention considers the preservation of heritage at the global level. underwater cultural heritage at its original locati- on, on the seabed, the first option, having prece- dence over all others. Objects may be collected Figure 3. The treasure of the wreck of the Nuestra Señora THE CONVENTION if this serves to rescue them from unavoidable de Atocha at Mel Fisher Days (www.schoonerwharf.com) destruction as a result of, for example, construc- tion work, or if collection constitutes a significant As a result, the period following World War II The 2001 UNESCO Convention on the Protecti- contribution to the protection and research of was noteworthy insofar as consideration was on of the Underwater Cultural Heritage aims to underwater cultural heritage. given for the first time to the need to afford more see states afford better protection to their

care to the methods of accessing individual underwater heritage. The cornerstones of the NO COMMERCIAL EXPLOITATION underwater finds, with the aim of properly pro- Convention set out the basic principles for the

tecting and researching underwater human heri- protection of cultural heritage, foresee a detailed The Convention establishes that there may be tage and preserving as much of the remains as system of cooperation among countries and es- no commercial exploitation of underwater herita- possible for posterity. As a counter to the looting tablish generally accepted rules for the treat- ge for the purpose of trade. Finds may also not undertaken by various private enterprises the ment and research of underwater cultural herit- be dispersed in a fashion that would prevent past half-century has seen a broadening of the Figure 4. Uluburun wreck - recovering ingots 1, 2 ge. (archaeologyhouston.wordpress.com) their subsequent location. These provisions are Conservation of Underwater Archaeological Finds - MANUAL 10 Bekiü L.: Underwater Cultural Heritage and the UNESCO Convention 11

in line with the moral principles applicable to OTHER KEY PROVISIONS The Annex makes several references to the con- cultural heritage on land and do not prevent ar- servation and restoration of finds. Rule 10, for chaeological research or tourist visits to archae- The Convention does not determine the example, which determines project design, also ological sites. ownership of individual finds and sites, nor does stipulates the obligation to draft a conservation it touch upon issues of state sovereignty and programme for artefacts and the site in coopera- TRAINING AND INFORMATION EXCHANGE declares that it shall not contradict other interna- tion with the competent authorities. In the chap- tional law, including UNCLOS, the United Nati- ter dedicated to funding and project duration, in States parties to the Convention should promote ons Convention on the Law of the Sea. Any sta- rules 17, 19, 20 and 21, there is specific mention the exchange of information and the transfer of te may sign this convention, independent of of the need to draft a contingency plan for fun- technology with the aim of improving the protec- whether it is a party to any other convention. ding and time required for conservation even in tion and research of underwater heritage. It also the event of the termination of the project or an encourages the provision of training in When adopting these principles the Convention interruption of expected funding. Of particular Figure 10. Mrs Irina Bokova addresing the 2011 Session underwater archaeology and international coo- also encourages ratifying countries to provide of the UNESCO 2001 Convention State Parties in Paris importance is chapter VIII of the Annex, rules 24 peration in the research, protection and mana- explicit protection to the cultural heritage of in- (Photo: L. Bekiü) and 25, which detail conservation programmes gement of underwater cultural property. It in par- land waters such as rivers and lakes. This paves for small finds and features during research, ticular emphasises the need to raise public the way for the participation of landlocked coun- THE ANNEX transport and the long - term storage of finds. awareness of the need to preserve underwater tries in the overall goal of protecting underwater heritage. heritage. The adoption of the Convention was followed by the adoption of the Annex to the Convention, States parties are also to notify other countries which stipulates in greater detail the practical in the event of the discovery of a shipwreck in aspects of the protection of underwater heritage. the area of their exclusive economic zone or in The Annex to the Convention sets out the rules international waters, with the aim of establishing that pertain to various activities directed at a coordinating country that will take measures to underwater cultural heritage. These are protect the site. generally accepted practical rules that are to be observed during excavation, such as the States parties shall train or develop their own methodology applied. It also establishes guideli- competent bodies that will see to establishing nes for how research projects and future preser- and maintaining a list of underwater cultural heri- vation should be conceived. The Annex also Figure 12. Vasa Museum Exterior (it.wikipedia.org) tage. These bodies will also secure the protecti- cites the qualifications researchers should pos- on, conservation, presentation and management sess to undertake activities related to the pre- of underwater heritage and nurture study and servation and management of underwater cultu- IMPLEMENTING THE CONVENTION education in this field. ral heritage. The rules contained in the Annex Figure 7. Mary Rose 2005 excavation site recorder map are one of the more important achievements of The supreme body of the Convention is the Me- (www.3hconsulting.com) the Convention and it is felt that every professio- eting of States Parties, convened at least once nal working in the field of underwater every two years. Expert and advisory support to archaeology should strictly abide by them. member states is provided by the Scientific and Technical Advisory Body (STAB), which pools some ten top experts in the field of underwater archaeology. Ad hoc States Parties Working Groups may also be established to discuss, among a limited number of participants, issues and to prepare working materials for Meetings of States Parties. The organisation and coordinati- on of these bodies and similar tasks is carried out by UNESCO, the Director-General and the Convention Secretariat based in Paris.

Figure 8. The stem of the Mary Rose is raised Figure 9. Mary Rose painting (www.3hconsulting.com) Figure 11. Vasa Museum Interior (traveling- (www.3hconsulting.com) kids.blogspot.com) Conservation of Underwater Archaeological Finds - MANUAL 12 Bekiü L.: Underwater Cultural Heritage and the UNESCO Convention 13

ral shipwrecks, the wreck of the Yongala in Aus- The Underwater Archaeological Finds Restorati- CONCLUSION tralia and the wreck of the Baron Gautsch in on and Conservation Department in Zadar, Cro- Croatia. Organised visits to underwater sites are atia was founded in 2007. It is now a part of In- From the beginnings of underwater research to in line with the guidelines of the Convention, ternational Centre for Underwater Archaeology the present day there has always been great which give preference to the in situ protection of in Zadar, a UNESCO category II centre. Conser- public interest for underwater cultural heritage. underwater heritage, and it is to be expected vation workshop pools a diverse team of In the past souvenirs were collected from that there will be a growing number of experienced conservators - restorers and che- shipwrecks, there were exciting articles in the underwater sites rendered accessible to visits by mists who have specialised in treating press, and many television and feature length divers. underwater finds. This handbook is their work films have been made on expeditions seeking and in it, in a concise fashion, they have endea- new underwater discoveries. It should, therefore, be in everyone's interest to voured to outline to those interested the met- protect underwater cultural heritage with the aim hods whereby various types of objects are pro- The number of specialised museums that exhibit of preserving it for future generations, and to tected. This work is largely based on their wealth restored and conserved underwater finds and develop the economic and tourism potential that of practical experience, and on a synthesis of even small vessels extracted from the seabed may emerge from its proper care. numerous expert papers on the subject from has now grown. Noteworthy are Sweden's Vasa around the world. Museum, visited every year by three quarters of This legal framework, which protects underwater heritage, must be adhered to at the national le- a million people, the museum at Bodrum in Figure 14. Caesarea location 14 (www.caesarea-diving.com) Turkey, the museum housing the once sunken vel, which, besides the adoption of the appropri- warship Mary Rose in Great Britain and many ate laws and regulations, implies practical work more. Improvements in diving techniques and targeted to protection. Above all this pertains to past century irretrievably lost, despite being kept equipment has seen a growth in the number of people involved in the protection and research in various collections and museum depots. tourist divers who make organised visits to of this heritage at the actual sites, most of who underwater archaeological sites. are underwater archaeologists. Other people not In recent decades some restorers and conserva- active in the systems of protection also come tors of archaeological finds have taken an inte- Underwater archaeological parks have been into contact with these locations. These are, rest in specialising in the protection of objects established where sunken architectural remains above all, divers - professionals involved in trai- collected in wet environments and in developing can be viewed, such as the Roman period port ning and guiding recreational divers. National various procedures and technologies to protect of Caesarea in Israel and the National Marine bodies, such as the maritime police, the port them. Protection Area in the Bay of Pozzuoli in Italy. authorities, coast guard and others who, as a Much more numerous, however, are the result of their competences, may play a key role frequently visited locations of shipwrecks such in the protection of archaeological sites, also as the Florida Keys Marine Sanctuary with seve- need to be included in the system of on - site protection.

Another key aspect - one that is, unfortunately, often overseen - is the protection of objects extracted from the water for the purpose of research. Early efforts to collect and research sunken objects did not give much heed to the conser- vation and restoration of the ob- jects extracted from the water. Consequently they were damaged or often entirely destroyed as a result of an abrupt change to the environment in which they were situated. This has seen countless Figure 15. Caesarea visitor's map (www.caesarea- Figure 13. Baron Gautsch wreck (Drawing: D. Frka; www.rovinj-online.net) very valuable finds collected in the diving.com) Conservation of Underwater Archaeological Finds - MANUAL 14 Mustaþek M.: Guidelines, Ethics and the Methodology of Conservation - Restoration Work 15

mes and teach; disseminate information gained written and pictorial records of all conservation - II. Guidelines, Ethics and the Methodology of from examination, treatment or research; promo- restoration interventions and diagnostic Conservation - Restoration Work te a deeper understanding of the field of conser- examination with the names of all those who vation - restoration. As the primary aim of con- have carried out the work. The conservator - servation-restoration is the preservation of cultu- restorer must strive to enrich her/his knowledge Mladen Mustaþek ral heritage, it is distinct from art and crafts. The and skills and cooperate and exchange informa- entific, social, or spiritual value are commonly conservator - restorer is distinguished from other tion with other professionals with the constant [email protected] designated "cultural heritage" and constitute a professionals by her/his specific education in aim of improving the quality of her/his professio- material and cultural patrimony to be passed on conservation - restoration. nal work. to coming generations. INTRODUCTION By definition the conservator - restorer is a pro- THE CODE OF ETHICS THE METHODOLOGY The protection of artistic heritage is as old as the fessional who has the training, knowledge, skills, OF CONSERVATION AND history of our civilisation. It is a complex process experience and understanding to act with the Every conservator - restorer should adhere to aim of preserving cultural heritage for the future. RESTORATION WORK that involves human activity and the will to pre- the principles, obligations and rules of behaviour serve artistic heritage from destruction or loss. The fundamental role of the conservator-restorer embodied in the code of ethics in the practice of is the preservation of cultural heritage for the When initiating conservation - restoration work The preservation of objects of archaeological their profession. As the profession of conserva- we must first undertake the careful examination heritage is the chief goal of conservation and benefit of present and future generations. The tor - restorer constitutes an activity of public inte- conservator - restorer carries out diagnostic of the object in question and its context. The restoration work. Conservation and restoration is rest, it must be practised in observance of all object must be carefully studied in order to pro- a lengthy process that often requires significant examination, conservation - restoration treat- pertinent national and European laws and agre- ment of cultural property and the documentation duce as appropriate as possible a determination financial resources. It consists of a series of pro- ements. The conservator - restorer works of what to do and how it should be done. In or- cedures, methods and interventions that prevent of all interventions. Diagnostic examination con- directly on cultural heritage and is personally sists of the research of relevant existing informa- der to gain the most proper and confident the further deterioration of objects, and restores responsible to the owner, to the heritage and to knowledge of the archaeological object under their physical integrity and visual identity. tion; the identification and determination of the society. Failure to observe the principles, obliga- composition and the condition of cultural herita- study a conservator - restorer may, during the Without the implementation of conservation and tions and prohibitions of the Code constitutes examination, undertake scientific analysis and restoration interventions most artefacts would ge; the identification of the nature and extent of unprofessional practice and will bring the profes- alterations and an evaluation of the causes of special surveys. The study of the archaeological decay, and the historic and artistic data would sion into disrepute. In their work conservator - object should yield insight into the kind of mate- be forever lost. deterioration. Conservation consists mainly of restorers contribute to a better understanding of direct action carried out on cultural heritage with rials and techniques used and the intentions cultural property, mindful of its aesthetic, historic inherent in the object's manufacture. Alterations In their work every conservator - restorer should the aim of stabilising its condition and retarding and spiritual significance and its physical further deterioration, while restoration consists of that an object has been subjected to over time adhere to the Professional Guidelines & Code of integrity. By his or her knowledge of the material should also be ascertained. Respectful of the Ethics. The Code of Ethics establishes the terms direct action carried out on damaged or deterio- aspects of objects possessing historic and artis- rated cultural heritage with the aim of facilitating integral object and of its history and context, the of reference and the definition of the conservator tic significant, the conservator - restorer pre- conservator - restorer shall critically assess - restorer's profession as confirmed and broade- its perception, appreciation and understanding, vents their deterioration and increases the while respecting as far as possible its aesthetic, which alterations act as disfiguring factors, ned at the general assembly of the European capacity of comprehension by emphasizing the which should - with the aim of facilitating the Confederation of Conservator - Restorers Orga- historic and physical properties. Documentation difference between what is original and what consists of an accurate pictorial and written re- perception, appreciation and comprehension of nisations (ECCO) held in Brussels in 1993. The has been replaced. In their work conservator - the cultural heritage - be removed, and which second version of the Professional Guidelines cord of all procedures carried out and the resul- restorers must adhere to the highest standards ting insight. Recommendations regarding stora- changes are an alteration of the original material was adopted at the Brussels general assembly of the profession regardless of the market value that it would be a mistake to eliminate (VOKIû on 1 March 2002, while the second version of ge, maintenance, display or access to cultural of the cultural heritage. All aspects of preventive heritage should be specified in this documentati- 2007, 261). the Code of Ethics was adopted at the general conservation should be taken into account befo- assembly held in Brussels on 7 March 2003. on. re carrying out interventions directly to cultural The real or potential value of cultural property heritage so that the conservator - restorer may may be destroyed by conservation - restoration Furthermore, it is within the conservator - limit the treatment to only that which is restorer's competence to: develop programmes, interventions. In order to avoid this the value of PROFESSIONAL GUIDELINES necessary. The materials used by the conserva- cultural property must be assessed and recogni- projects and surveys in the field of conservation tor - restorer should be compatible with the ma- zed. In order to define a proposal of actions and - restoration; provide advice and technical assis- terials of the cultural heritage and as completely The objects, buildings and environments to the order in which they are to be conducted, the tance for the preservation of cultural heritage; reversible as possible. Every conservation - res- which society attributes particular aesthetic, arti- conservator - restorer must establish the prepare technical reports on cultural heritage; toration treatment of cultural heritage should be stic, documentary, environmental, historic, sci- following: the nature of the original material and conduct research; develop educational program- documented, and the report should include

Conservation of Underwater Archaeological Finds - MANUAL 16 Mustaþek M.: Causes of the Decay of Archaeological Material 17 the production technique applied; what changes de for and secure a methodological approach to III. Causes of the Decay of Archaeological to the material and which additions to the materi- conservation - restoration work; to establish the al have occurred as a consequence of the pas- intention and value contained in the cultural heri- Material sage of time; which changes are a disfiguring tage; to determine the material to be preserved factor and which are acceptable; what are the and changes that have occurred (VOKIû 2007, Mladen Mustaþek The environmental factors that can affect both reasons for undertaking the intervention on the 258). Conservation - restoration documentation [email protected] the deterioration and the preservation of an arte- object; what is the entirety of the object and its should include: inventory data that establishes fact are: physico - chemical, biological and mec- context; what was the history of the object, what the heritage in question, research documentati- hanical. were the intentions of its author and what value on, work proposal drafts, the documentation of

is inherent to the object (VOKIû 2007, 262). conservation - restoration work, instructions for INTRODUCTION

the method of preservation and maintenance The determination of the method in which con- and photographic records of the appearance Like other materials in the natural environment, PHYSICO - CHEMICAL CAUSES OF servation - restoration work is to be conducted is and condition in all phases prior to and after the underwater archaeological material is exposed DAMAGE followed by the selection of materials and proce- intervention (VOKIû 2007, 259). over time to the effects of its environment and is, dures to be applied. Materials and procedures as such, subject to change. There are numerous WATER are determined for each phase of conservation - and diverse physico - chemical reactions that restoration work. The following principles are to 5. CONCLUSION are referred to as natural aging. The dynamics Water is a complex medium consisting of pure be respected in the selection of materials and of these reactions affects the quality and water, mineral salts, dissolved gases and micro procedures: the principle of minimal necessary The responsibility and the gradations of the work durability of a material. The process of deteriora- and macroorganisms (MEMET, 2007, 153). intervention; the principle of visual and structural of a conservator - restorer are established by the tion is a natural one and its speed varies for ea- Water is known as the universal catalyst as it compatibility of the materials and procedures Code of Ethics. Given that conservator - resto- ch material (MUŠNJAK 2008, 132). The nature activates other causative agents of deterioration, applied with the original materials and original rers work with historic originals, which possess of the substance from which the archaeological facilitates and accelerates most chemical reacti- techniques of manufacture; the principle of the artistic, religious, scientific, cultural, social and material is made and the microclimatic environ- ons and allows organisms to develop. Submer- reversibility of the materials and procedures ap- economic value, the conservator - restorer has ment in which it is situated affects the deteriora- ged artefacts may be damaged by the activity of plied; the principle of the distinctness of the in- particular responsibility for the preservation of tion of the archaeological material. Some types other components besides pure water, such as tervention and the principle of sustainability their physical integrity. The professional guideli- of macro and microorganisms find a suitable salts, dissolved gases, organic substances and (VOKIû 2007, 263). The professional guidelines nes establish the fundamental role of the con- habitat for their development on objects of ar- undissolved particles. divide the concept of preservation into the terms servator - restorer as being the preservation of chaeological heritage. The living species that preventive conservation and remedial conserva- cultural heritage for the benefit of present and inhabit these materials range from microscopic The physic - chemical action of water on tion (PEDIŠIû 2005, 12). The preventive conser- future generations, and to contribute to a better bacterial cells to plants and animals (TIANO underwater artefacts causes various types of vation of an object of cultural heritage consists understanding of its aesthetic and historic attri- 2010, 1). damage. Water causes ceramic, stone and of indirect actions, while remedial conservation butes (PEDIŠIû 2005, 12). According to the co- glass objects to become saturated with the salts consists of direct action on the cultural property. de of ethics the work of the conservator - resto- In long term exposure to a given set of conditi- present, which leads to the weakening of the Restoration involves direct action on cultural rer encompasses the technical examination, ons a material will tend to achieve a state of material's structure, delamination and the dama- property that is deteriorating or has been dama- preservation and conservation - restoration of equilibrium with the environment in which it is ging of the surface of the material. The effect of ged, with the aim of facilitating the understan- works of art. When undertaking restoration pro- deposited. And while it may be slow, the deterio- water on objects made of metal encourages the ding of the cultural property. To reduce direct cedures the conservator - restorer should also ration of archaeological material is inevitable. development of a very intensive process of cor- intervention on cultural property to the smallest endeavour to apply those products, materials The extraction of archaeological material from a rosion that destroys the metal structure of the possible measure the conservator - restorer and procedures that will not have a negative marine environment leads to a change in the object and irreparably damages it. Artefacts ma- must take into consideration all preventive con- effect on the work of art. Restoration documen- primary microclimatic environment, and upsets de of wood and other organic materials are most servation options when determining restoration tation must contain all relevant data related to the state of balance established between the sensitive to the action of water. Besides the fact procedures. the procedures conducted on the cultural material and its environment. Atmospheric ef- that water is the chief agent of biodegradation, it property. This restoration documentation beco- fects begin to act upon the material that encou- also penetrates the organic structure of the ob- Written records and photographic documentati- mes a part of the work of art, also as determined rage and accelerate numerous decomposition ject causing the weakening of the organic struc- on based on a defined system must be kept du- by the professional guidelines (PEDIŠIû 2005, processes. The timely conduct of appropriate ture of the object. Many organic materials conta- ring conservation - restoration work. This system 13). conservation procedures is, therefore, in water in the structure of their fibres and cells is known as conservation - restoration documen- necessary with the objective of stabilising the that is balanced with the surrounding atmosphe- tation; it is an integral part of the cultural herita- artefact, retarding the further deterioration of the re. ge and must be accessible. Conservation - res- material, and of ensuring its safekeeping until toration documentation has as its goal: to provi- conservation procedures can be undertaken. When they are exposed to a drier or wetter envi-

Conservation of Underwater Archaeological Finds - MANUAL 18 Mustaþek M.: Causes of the Decay of Archaeological Material 19

ronment they are deformed (shrink or swell), more soluble at low pH levels, while silicates are greater concentration of oxygen in the sea indu- terial. These conditions also facilitate various whereby the original form of the object is lost. more soluble at higher pH levels. Salts dissolved ces an increase in the corrosive potential of me- chemical reactions and are favourable to the in seawater contribute to the formation of a cor- tal objects such as copper and iron, and materi- development of microorganisms that lead to de- SALTS rosive environment as they act as electrolytes als at greater depths are often better preserved composition and the deterioration of the organic that accelerate the electrochemical corrosion of because of the lower quantity of oxygen present structure of materials (UNGER, SCHNIEWIND, Salts are ionic bonds created by a reaction metals, leading to their decomposition (MEMET, (MEMET, 2007, 155). Chemical bonds with UNGER, 2001, 23). between an acid and a base. When dissolved, 2007, 152). oxygen are referred to as oxides, and the chemi- salts split into individual ions, calcium (Ca2+), cal reaction of bonding with oxygen, oxidation. On metal objects a high percentage of relative bicarbonate (HCO3-), sodium (Na+) and chloride Soluble salts on porous archaeological material humidity activates corrosion processes, (Cl-). Unlike soil and internal waters, most such as ceramics and stone may cause signifi- As an elementary substance oxygen is one of especially on objects that have not undergone seawater contains soluble salts. The chief ions cant damage, especially upon being brought up the chief components of air, accounting for 21 conservation treatment, and to a lesser extent present in seawater are Na+ and Cl-, and the to the surface. Artefacts extracted from the sea percent. It is necessary to the sustainment and on objects that have undergone conservation level of SO42- is also high. must be kept submerged in water until the desa- development of almost all living organisms - it treatment. The detrimental impact of humidity on lination process; otherwise the evaporation of participates in diverse biochemical processes. ceramic, stone and glass artefacts is most evi- Cations (g/L) Anions (g/L) water could lead to the crystallisation of soluble The solubility of oxygen in water, i.e. the ability dent on artefacts that are dried and stored Na+ 11.04 Cl- 19.88 salts, increasing their volume and the fracturing of water to bond oxygen, depends on the tempe- following extraction from the sea without having 2+ 2- Mg 1.30 SO4 2.74 of the structure of the material. rature. The lower the temperature of water, the undergone the desalination procedure. An ele- Ca2+ 0.42 HCO3- 0.18 more oxygen it can bind, and conversely, the vated percentage of relative humidity causes the K+ 0.39 Br- 0.07 Upon extraction to the surface underwater arte- higher the temperature of water, the lower its dissolution and migration of soluble salts in the Sr+ 0.008 F- 0.015 facts are exposed to atmospheric influences that capacity to bind oxygen. The level of oxygen in structure of materials. With a reduction of relati- Table 1. The concentration of the most prevalent ions in also contain soluble salts. Large quantities of water varies significantly but is greater in ve humidity, the salt re - crystallises, which cau- seawater Na+ and Cl- can be created from seawater or shallower surface strata and at depths where ses it to expand in volume and fracture the salt saturated aerosol (windborne seawater). photosynthesising plants release oxygen or structure of materials. Salinity, i.e. the total mass of dissolved salt, is Particular attention should be given to this fact if where oxygen-rich water is carried by sea cur- not the same in all marine environments and the underwater artefact is exposed in an open rents. LIGHT differs based on geographic area. The average area that is not protected from atmospheric influ- salinity of global seas is 35‰, while the salinity ences. Salt in the air in combination with HUMIDITY AND TEMPERATURE There are natural and artificial sources of light. of the Adriatic Sea is 38‰. All salts are soluble humidity and other compounds and particles in The sun is the most important natural source of to a certain degree, but the solubility of some is the air create electrolytes on metals that facilita- Absolute humidity is the quantity of water vapour light. By sunlight we mean the form of energy we negligibly small, and we refer to these salts as te electrochemical corrosion and the deteriorati- in the air. The quantity of water vapour in the air refer to as electromagnetic radiation. This radia- insoluble. Salts of relatively high solubility are: on of metals (SCOTT, EGGERT, 2009, 109). depends on the temperature. Warmer air can tion varies in wavelength. Of the total flow of nitrates, chlorides, sulphates, bicarbonates and Soluble salts in the atmosphere are most often contain more water vapour than cooler air energy radiated from a source of light, the elec- acetates, while those of low solubility are silica- deposited on the surface of materials. Surface (MUŠNJAK 2008, 133). A drop in temperature tromagnetic radiation from a wavelength of 780 tes, oxides, sulphides, phosphates and carbona- damage caused by deposits is most frequent in under the dew point leads to condensation in to 380 nm is referred to as the visible part of the tes. Other factors, such as pH value, also affect ceramics and stone, but other porous materials which water vapour changes from a gaseous spectrum. Above and below this part of the solubility. Carbonates, oxides and sulphites are are also subject to damage caused by soluble aggregate state to a liquid. The concept of relati- spectrum are the infrared (IR) and ultraviolet salts (CRONYN 1990, 23). Like soluble salts, ve humidity refers to the ratio of absolute (UV) ranges. The IR range covers the

Origin Salinity (‰) insoluble salts may form deposits on any arte- humidity in the air at a given temperature and wavelengths from 1—m do 780 nm. This thermal Rivers (mean world fact. The exposure of material to the effects of the quantity of water vapour needed to achieve radiation from the sun makes life on earth possi- value) 0.1 insoluble salts usually causes surface damage the dew point at the same temperature. Humidity ble. UV radiation from 380 to 100 nm is vital be- Baltic Sea <17 and changes in the colour of materials. and temperature have an impact on underwater cause of its biological effect, but also particularly Black Sea 18–22 artefacts from the moment they are taken from detrimental in the UV-C range (ozone hole). OXYGEN the sea and are exposed to atmospheric influen- Atlantic and ces. The effect of humidity and temperature on Photochemical changes to materials are caused Pacific Oceans 32–35 The presence or absence of oxygen is the chief underwater artefacts varies and depends on the by the quantity of light energy that the material is Mediterranean Sea 39–47 controlling factor in the activity of organisms that type of material and the conservation condition able to absorb. The absorption of light on a ma- Adriatic Sea 38 cause the decomposition and deterioration of of the object. The impact of extremes in relative terial does not always have to lead to chemical Red Sea 43–45 archaeological material. Oxygen is a component humidity or elevated temperature on objects of changes (SCHAEFFER, 2001, 6). Sunlight has Dead Sea 276 of many chemical reactions that directly or wood or other organic materials may lead to an indirect effect on the deterioration of artefacts Table 2. Salinity in various marine environments indirectly lead to the damaging of material. A temporary or permanent deformation of the ma- in an underwater environment, as it is essential

Conservation of Underwater Archaeological Finds - MANUAL 20 Mustaþek M.: Causes of the Decay of Archaeological Material 21

GYSELS, 1998, 2327). On organic material at- gical toxicity, the phenomenon is less prevalent mospheric pollution can lead to elevated acidity (MEMET, 2007, 164). and the weakening of the structure of materials. On metal objects atmospheric pollution can in- The appearance of a given fouling organism on duce detrimental corrosion processes, while on archaeological artefacts depends on various ceramic and stone objects it can lead to the stai- factors, such as temperature and salinity values, Table 3. The electromagnetic spectrum ning and bleaching of surface areas and chan- the concentration and saturation of oxygen and ges in the colour of the object. the type and amount of time the material has to the survival of fouling organisms, which have tal, ceramic, stone and glass, in spite of their low been submerged. Fouling organisms on archae- a much more detrimental effect on materials. sensitivity to light have a maximum recommen- ological material causes various kinds of dama- The effects of light on underwater artefacts are ded exposure value of 300 lux. THE BIOLOGICAL CAUSES OF ge. Macroorganisms, such as molluscs, usually more significant in a dry environment where di- DAMAGE cause physical damage to archaeological mate- rect exposure to UV radiation can cause detri- POLLUTED AIR rial, in particular wood and other organic materi- mental changes to materials. Artificial sources of als, while microorganisms encourage corrosion FOULING ORGANISMS light - common light bulbs, halogen wolfram By its composition air is a mixture of gases. Its processes on metal and are the chief causal

bulbs and fluorescent bulbs - also emit UV and composition changes depending on geographic agent of the effect of biological decomposition The biological causal agents of the decay of heat radiation. To reduce their detrimental ef- position and in its natural state it contains a cer- that causes surface damage and the weakening underwater artefacts are fouling organisms, fects they must be covered with special protecti- tain percentage of water vapour. Along with the of the structure of materials. When the life cycle which we can divide into micro fouling organi- ve films with UV filters (SCHAEFFER, 2001, 26). normal gases, air may also contain some other of fouling organisms on colonised artefacts sms and macro fouling organisms. Fouling orga- Damage from direct exposure to UV radiation gaseous and solid matter we refer to as atmosp- ends, their remains are deposited and limestone nisms are animals and plants that are a compo- depends on the sensitivity of individual types of heric contaminants. Gases such as sulphur and and other sedimentary rock form organogenic nent part of marine, river and lake biomasses. material. UV radiation can cause the bleaching nitric oxides, carbon monoxide and dioxide, sediments on materials (ŠESTANOVIû 1997, Micro fouling organisms such as bacteria and of the surface of an object, the weakening and chlorine, hydrogen peroxide, hydrogen sulphide 115). The formation of sediments on artefacts algae have a detrimental impact on materials in fracturing of the structure and cause it to fall and others cause air pollution. Polluted air may leads to the creation of a local microenvironment an underwater environment, while in dry envi- apart. The inorganic materials ceramic, stone, also contain large quantities of water vapour, that protects the material from direct exposure to ronments, besides bacteria, moulds, fungi and glass and metal have a low level of sensitivity to smoke and dust. Smoke in the air may originate the environment and further accelerated decay. lichens. Numbered among the macro fouling UV radiation, while pigments and organic materi- from the incomplete burning of wood, natural In these isolated environments the process of organisms in underwater environments are: co- als such as wood, textile and leather are much gas and petroleum derivatives or coal. Smoke decomposition is retarded. Sedimentation is the rals (Anthozoa); molluscs (Mollusca); polychaeta more sensitive to UV radiation, and paper is very contains tar substances that can accumulate on only natural process that provides for the partial (Polychaeta); crustaceans (Crustacea); echino- sensitive. UV radiation can also damage protec- the surfaces of objects over time, creating a preservation of iron finds, which, if directly derms (Echinodermata) and fish (Pisces), while tive coatings such as resins and lacquers on sticky mass of brown or black colour, thus impai- exposed to the activity of the sea, would in dry environments they include insects and already conserved and restored artefacts, which ring the aesthetic aspect of the object. completely erode and decay (SCOTT, EGGERT, rodents. Fouling organisms inhabit almost all may activate deterioration process in the materi- 2009, 123). types of archaeological materials, with the al. IR radiation on archaeological material cau- There are three chief sources of contaminated exception, for example, of objects made of cop- ses it to heat up. air that can have a detrimental effect on archae- MICROORGANISMS per and bronze on which, because of their biolo- ological objects: All sources of light cause a certain amount of Microorganisms are primitive organisms very heating. An increase in temperature impacts the • The external environment, which produ- sensitive to the environment. They are also not relative humidity in the air and the percentage of ces dust and atmospheric contaminants; resistant to high levels of salts and the toxic pro- humidity of the artefact. Heating caused by artifi- • The environment in a museum or depot ducts of copper corrosion and certain organic cial sources of light cause drying and an elevati- which may be exposed to dust or conta- chemicals. Some kinds of microorganisms have on of temperature that accelerates the process minants created by restoration work in adapted and are resistant to extreme pH levels, of the decomposition of material. The recom- workshops; desiccation and oxygen deficiency. The metabo- mended maximum value of light exposure for • Materials used for storage or the lism of microorganisms is not particularly effecti- highly sensitive material such as textile, leather exhibition of objects that may contain har- ve and, instead of carbon dioxide, they secrete and paper is 50 lux. Materials with moderate mful chemicals. organic acids. Individual microorganisms are not sensitivity such as wood, bone, and materials visible to the naked eye, but their colonies are with a protective coating such as resin and Elements of atmospheric pollution can cause (CRONYN 1990, 15). The effects of these orga- lacquers have a maximum recommended detrimental chemical reactions on almost all Figure 1. Object covered by organogenic sediment nisms on materials, known as biodegradation, (Photo: M. Mustaþek) exposure value of 150 lux, while artefacts of me- types of material (VAN GRIEKEN, DELALIEUX, are most evident in organic materials and are

Conservation of Underwater Archaeological Finds - MANUAL 22 Mustaþek M.: Causes of the Decay of Archaeological Material 23

part of the natural cycle of decay. The effects of porting the growth of biological causes of corro- unlike other organisms, do not require oxygen and heat, while some species may also have a the waste by - products of the metabolic proces- sion such as moulds and lichens (KUMAR, KU- for respiration. They secure nourishment by the detrimental effect on health (UNGER, ses of microorganisms such as organic acids on MAR 1999, 19). Algae may also cause biodegra- reduction of inorganic chemicals such as nitra- SCHNIEWIND, UNGER 2001, 108). archaeological material may cause chemical dation. They produce various metabolites, for tes, carbon dioxide, manganese (IV) and iron weakening and accelerate its decay. The appea- the most part organic acids, which have an acti- (III). This method of respiration is inefficient and FUNGI rance of an artefact may also be visually deterio- ve effect on materials causing their decay and ineffective and as a result bacteria secrete orga- rated by pigment particles created by mycelium, permanent damage. nic acids instead of carbon dioxide, which me- Fungi are numbered among the most detrimen- bacteria or black sulphide created by the activity ans that they are able to colonise anoxic depo- tal of organisms responsible for the biodegrada- of anaerobic sulphate reducing bacteria, while BACTERIA sits. A number of these bacteria cause the des- tion of organic and inorganic materials. The me- the surface of an object covered in microorgani- truction of organic artefacts, while some have an tabolic diversity of this group of microorganisms sms may be unrecognisable. Bacteria are single - celled microorganisms, and indirect effect on organic and inorganic materi- increases their ability to colonise various types the single largest group of life forms. They are als. Noteworthy among these are anaerobic sul- of substrate (wood, glass, stone). Fungi are for- ALGAE invisible to the naked eye, propagate quickly phate reducing bacteria (SRB) such as Desul- med of a vegetative filamentous body of and can form colonies of several million units in phovibrio, which reduces sulphate to sulphide. mycelium, composed of series of identical cells Algae are a broad group of simple, mostly water the space of a few hours. Their size ranges from The presence and activity of these bacteria indi- called hyphae, and a reproductive system called inhabiting, photosynthesizing organisms one to several microns. In unfavourable conditi- cate the danger of salt efflorescences and acid the fruiting body. Spores develop in the fruiting (ranging from unicellular to multicellular) similar ons bacteria create special, very resistant cells - attack of the object after its drying. It can be de- body that, in ideal conditions for growth, create to plants. Algae are able to live in neutral to spores, which they can also use to multiply. termined by the odour of rotten eggs (hydrogen new hyphae cells. There are certain physical, weakly alkaline environments, in extremes of Spores are very robust: they can endure long sulphide) and the blackening of deposits caused chemical and biological conditions necessary for temperature and salinity, and in environments drought, various chemicals and both high and by the formation of metal sulphides (CRONYN the growth of fungi such as temperature, moistu- ranging from total darkness to sufficient light. low temperatures (MUŠNJAK 2008, 138). Bacte- 1990, 17). re, light, the presence of oxygen, the pH value of Algae are divided into seven classes, and colour ria use enzymes to break down organic substan- the substrate, and the type of material, which of algae varies from red to dark purple, which is ces they use as food. MOULDS have different effects on the development of cer- the result of a mixture of various pigments. The tain types of fungi. names of individual divisions and classes of al- Moulds are multicellular organisms of plant ori- gae are derived from their colour. A common gin at a higher level of development than bacte- The fungi that cause the decay of organic mate- trait of all algae is photosynthesis, which produ- ria. Moulds may be brilliantly coloured, black or rial can be divided into two groups: fungi that ces oxygen as a by-product and supplies it to white - depending on the species. They are re- cause staining (stain fungi) and fungi that cause aqueous environments. In relation to the sub- cognisable as white, green, red or black blemis- decomposition/rotting (rot fungi). Staining fungi strate they inhabit we can divide algae into two hes of circular form, and from the odour of mo- do not directly degrade cell walls and do nor groups: epilithic algae, which grow on the surfa- uld. Active mould appears dirty or slimy. Dor- cause a significant reduction in their sturdiness, ce of the substrate; and endolithic algae, which mant mould is dry, like talc. Moulds are unable while rot-causing fungi attack the primary com- penetrate and colonise the interior of the sub- to assimilate carbon from the air and live as pa- ponents of the material's cell wall, causing chan- strate (KUMAR, KUMAR 1999, 18). rasites on other organisms. Moulds reproduce ges in chemical, mechanical and physical traits through spores or by the fragmentation of (LIPANOVIû 2009, 2). A high percentage of mycelium. Mould spores are created in favoura- humidity and an environment saturated with ble conditions in four to seven days. Mould spo- water are the optimal conditions for the appea- Figure 3. Black sediment created by the decay and res are light and, like bacteria, they can remain rance of soft rot fungi, which attack the decomposition of iron (Photo: M. Mustaþek) airborne over great distances. In very unfavoura- secondary components of cell walls and ble conditions moulds may lay dormant for completely destroy them (ARROYO, 2009, 42). Figure 2. The algae covered barrel of a bronze cannon The effects of bacteria on archaeological materi- years, and are very quickly activated in favoura- (Photo: M. Mustaþek) al may lead to permanent damage caused by ble conditions. Mould mycelium die off quickly in LICHENS the degradation and decomposition of materials. unfavourable conditions, while their spores sur- Algae can influence the deterioration of archae- When present on an artefact in greater numbers vive. Special disinfection compounds are Lichens are multicellular composite organisms ological material by causing physical and chemi- bacteria appear in the form of coloured blemis- required to destroy them (MUŠNJAK 2008, 139). that are formed by the symbiotic association of cal damage. The effect of algae on archaeologi- hes, since many of them create particles of pig- Moulds are able to colonise various types of ma- two plant organisms - fungi and algae. This cal objects is usually the loss of aesthetic value. ment, incrustations and black sediment. Bacteria terial and may cause damage not only to symbiotic relationship allows them to survive in And while the direct damage to material caused secrete enzymes that decompose organic sub- wooden surfaces, but also to paper, glue, leat- extremely dry and wet environments. They differ by algae is not always significant, they indirectly strates and , like fungi, are aerobic. There is a her, textile and other materials, especially in the greatly in colour and shape, and their appearan- influence the deterioration of materials by sup- strain of bacteria that are anaerobic and that, presence of relatively high levels of moisture ce depends for the most part on the structure of

Conservation of Underwater Archaeological Finds - MANUAL 24 Mustaþek M.: Causes of the Decay of Archaeological Material 25

the fungi. Lichens are the best known of the cooler temperatures slow their activity. As they the erosion of rock, the transfer of substances applied to the study of the mechanisms of dete- epiphyte plants. As individual organisms they use wood as a source of food, they bore canals and the deposition of particles. Most of the ma- rioration on various cultural heritage objects. are aerobic and secrete a significant quantity of into it, in which calcareous deposit terial that is deposited in the sea comes by way Physico - chemical and biological factors such organic acids (CRONYN 1990, 16). Their stratifi- subsequently form (UNGER, SCHNIEWIND, of rivers. These are either particles or dissolved. as humidity, heat, light, bacteria, organisms and ed structure guarantees lichens a long life span UNGER 2001, 134). The actual boring of canals algae are causes of deterioration that have a even after years of drought. A small number of into wood weakens its structure, leading to the There are three basic types of sediment in the direct or indirect effect on materials, leading to lichens live in waters and seas. Lichens are cracking and fracturing of wooden structures. sea: detrimental changes. The speed at which a ma- highly sensitive to air contaminants, especially Besides as a source of food organic and other terial achieves a state of equilibrium with its en- to industrial pollution high in carbon dioxide. Lic- archaeological materials may also provide a ha- • Lithogenous – particles that are transpor- vironment is determined by the characteristics of hens reproduce by producing spores. They are bitat for some organisms. ted to the sea by river, wind and ice and the microclimatic environment. Climate is for the released into the air to find the right algae in or- are created by the weathering of all types most part determined by temperature and the der to establish a new symbiosis. of rock on land. relative humidity (RH) of air. Materials gradually MECHANICAL CAUSES OF DAMAGE • Hydrogenous – are created by precipitati- change under the influence of environmental Lichens can affect archaeological heritage ob- on directly from a solution. Marine evapo- factors such as oxygen level, moisture and light. jects both physically and chemically. Physical Mechanical damage to underwater archaeologi- rites are created by deposition for the Organic materials such as bone, paper, textile damage occurs by the penetration of hyphae cal heritage is caused by human and natural most part in semi-closed basins such as and wood are subject, for example, to the split- into pores and the expansion and contraction of factors. The leading human factors affecting the coastal lagoons. Halite accounts for the ting or the polymerisation of molecules and the thallus resulting from changes in moisture, in degradation of sites are: the non-professional majority of precipitated material. oxidation. These chemical processes are acce- the process of which there is damage to the sur- extraction and handling of objects, the looting of • Biogenous – organisms create organo- lerated by elevated temperatures - the higher face of the object causing the formation of pits archaeological sites, find disturbance by divers, gens. Biogenous sediments consist of the the temperature, the quicker the aging process. and holes (KUMAR, KUMAR 1999, 22). Lichens fishing activity (mussels, fishing nets), the an- skeletal remains of organisms and of or- A high percentage of humidity accompanied by cause chemical damage to archaeological mate- choring of vessels, underwater construction ganic substances. The majority of the cal- elevated temperature favours the development rial by secreting organic acids. They have a cor- work, waste dumping at sites and other factors. cium carbonate that is deposited in the and growth of most biological destructive fac- rosive effect on the substrate created by the re- Numerous natural factors also cause damage to sea is of biogenous origin. tors. With an understanding of the mechanisms lease of metabolite acids. Metabolite acids cau- of deterioration and timely acti- underwater artefacts, such as sea currents, se chemical damage to the material by breaking which, for example, carry sand and cause its on taken to retard and prevent down and disintegrating the substrate. abrasive action against archaeological material the further development of detri- leading to extensive damage to the surface of mental processes on objects of MACROORGANISMS the artefact, waves, various natural catastrophes archaeological heritage, we are and the accumulation of sediment. making great strides with regard Macroorganisms such as animals and plants to safeguarding their physical require oxygen for respiration and as such can- Archaeological material, once deposited on the integrity and long - term preser- not function in an environment lacking oxygen. seafloor, riverbed of the bottom of a lake, is vation. In order to survive all organisms require water in exposed to the inevitable accumulation of sedi- some degree. Organisms are not resistant to ment. Sediments that form over time subject desiccation, extreme cold or heat. Noteworthy artefacts to significant pressure, which causes among the living communities in the seas are the cracking and fracturing of the archaeological corals (Anthozoa); molluscs (Mollusca); bristle material. The action of a strong sea current worms (Polychaeta); crustaceans (Crustacea); shifts larger and heavier element of archaeologi- echinoderms (Echinodermata) and fish (Pisces). cal material and sediment, laying them on more Figure 4. A site covered by sediments (Photo: HRZ archives) These macroorganisms most often cause fragile objects, which also leads to their cracking physical damage to archaeological material. So- and fracturing. The speed of the sedimentation CONCLUSION me molluscs, for example, can bore canals into varies significantly in individual environments wood and stone, causing stains, fading and the and ranges from 1mm to several centimetres per An understanding of the mechanisms of the de- porosity of the material. Major damage to year. Sediments are very diverse and the vast terioration of materials, combined with an under- wooden objects in the sea is caused by the majority of seabed, riverbeds and lakebeds are standing of the factors that cause detrimental shipworm (Teredo navalis). It belongs to a group covered in them. The bottom contains the rema- changes, is of exceptional importance. A of molluscs whose development depends on the ins of land erosion, mussels, the organic rema- growing number of analytical techniques have salinity and temperature of the water, such that ins of organisms and salts that have precipitated become available in recent decades that can be a warm climate favours their development, while from seawater. The sedimentary cycle includes

Conservation of Underwater Archaeological Finds - MANUAL 26 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 27 IV. The Conservation and Restoration of Ceramics paste porcelain, stoneware) which the greatest roles are played by porosity and capillarity. The external factors of degradati- and Pottery In the first group we can include unglazed on may be divided into two major groups: natural pottery dating from prehistory onwards, fired on and human. Marine environments are characte- Martina ûurkoviü open bonfires or in primitive kilns that achieved rised by physical (abrasion, transport, depositi- es. After firing most take on a reddish colour as temperatures ranging from 500 to a maximum of on), chemical (dissolution - precipitation, [email protected] a result of the presence of a large quantity of 700°C, Roman period, medieval and all other oxidation - reduction) and biological (bacterial or iron oxides. The chief characteristic of kaolin glazed and unglazed ceramics fired in closed benthic organism growth) processes (LOPEZ - and clay is its plasticity or ability to retain defor- kilns that achieved the appropriate temperature ARCE 2013, 2031-2042). INTRODUCTION mation in spite of the absence of the force that for firing ceramics of about 800 to 950°C (e.g. caused it. terra sigillata at 900 - 950°C in an oxidation am- The degradation of materials is usually accelera- Ceramic finds are the most frequent at bient to achieve the bright red colour of the slip), ted or activated when we remove the object from underwater archaeological sites. The discovery Different substances are added to the clay and post medieval and other ceramics fired at the environment in which it was deposited and in of ceramics profoundly changed the way people primarily to give the paste greater resistance, to high temperatures that do not exceed 1000 - which it had achieved a state of equilibrium, lived. Its permeability and durability provided for support temperature changes during firing, to 1200°C. These may be objects with various ap- even if imperfect, and we place it in another en- the preservation, storage and transport of goo- accelerate drying, to decrease the retraction that plied coatings or without, produced from com- vironment. The most evident example of this is ds, and changed human nutritional habits. The occurs during drying, to reduce the plasticity of mon red or white clay or some other common the extraction of a find from an underwater envi- principles of ceramic manufacture have remai- the paste and to lower the required firing tempe- clay. ronment in which it was conserved and quite ned largely the same over time. It is based on rature. These substances include sand, quartz, stable for thousands of years, causing it to dry the modelling of earth, i.e. clay, followed by its plagioclase, potassium feldspar, rock fragments, We find examples of the second group in hard out in the air, leading to cracking and fracturing. firing at high temperature until a firm mass is powdered fragments of ceramics (grog), straw, porcelain already in use during the early medie- We need to help these objects gradually adapt achieved. Manufacturing techniques have been feathers, shale, granulate slags or crushed val period (China, Korea, Japan), the soft-paste to the new conditions. The same happens with perfected over time. It all started with the simple shells (LOPEZ - ARCE 2013, 2031-2042). It is th and bone china in use since the 18 century objects deposited underground. Upon their manual shaping of a piece of clay, quickly these particles that are visible in the structure – (Europe), and the stoneware and fire clay that extraction from the site the objects are exposed followed by the invention of the manual potter's unique to every piece of pottery – and the type are fired at very high temperatures ranging from to new conditions such light, changes in tempe- wheel, the fast potter's wheel, modelling by im- of clay used that are one of the means of diffe- 1000 - 1400°C. rature, changes in the level of humidity and con- pressing the clay or pouring liquid clay into mo- rentiating ceramics. The porosity of ceramics tact with living organisms. ulds, the use of presses and so forth. depends on the extent to which the minerals

have been fused, the size of the particles of the CERAMIC DETERIORATION The chief natural factor leading to degradation is Unfired objects can be coated with white liquid cited tempers, and the quantity of organic mate- water, which acts both as a physical and a che- clay and then engraved and/or decorated with rials that will burn away at high temperatures Degradation and alteration are natural pheno- mical factor, and is also a requisite for the pre- various engobes or mineral pigments and then leaving cavities in their place. At lower firing mena in the lifetime of every material. It begins sence of biological factors. The physically des- fired. The glazes were applied and then fired for temperatures (800°C) the individual mineral while the material is still in its original form, and tructive activity of water in the event of the free- the second time, which made the objects imper- temper grains are easily distinguishable from the continues in the forms humans have shaped it zing of water in the pores of material is signifi- meable to water. clay matrix; at higher firing temperatures (1000- into. The process is constant and unstoppable, cant. The ice crystals formed have a volume 1050°C) the sintering process produces an in- and restorers can undertake a series of operati- much greater than that of water, which causes Clays are formed by the alteration of feldspathic crease in the interconnection among these gra- ons on the object only in an attempt to slow the stress within the pore and leads to the cracking rocks under the influence of atmospheric ins and the matrix causing the porosity to decre- process. Alteration refers to the aging of objects of the walls of the pore. The phenomenon of agents: rain, rivers, winds and the release of ase (LOPEZ - ARCE 2013, 2031-2042). accompanied by change that does not have a repeated freeze - thaw cycles lead to a loss in gases from the Earth's crust. Chemical reactions direct effect on the preservation of an object and the readability of the surface and finally to the turn feldspathic rock into kaolinite (Al2Si2O5(OH) We can divide pottery into two major groups ba- that does not impair its readability. This category complete destruction of an object. Water is also 4). If this process occurs within the rock itself, it sed on the firing temperature: of change includes alterations of colour, the for- a medium for soluble salts - the most frequent is then possible to extract pure kaolinite from the mation of a superficial patina on objects and so rock. Crushing this into a fine white powder pro- • Ceramics fired at lower temperatures (fine cause for the degradation of porous materials and coarse unglazed pottery, glazed forth. Degradation occurs as the advanced pro- extracted from the sea or environments close to duces kaolin that, with quartz and calcite, is a cess of aging accompanied by a loss of the basic component of porcelain. If this process pottery, engobed pottery, majolica and the sea. Seawater contains different types of object's readability. occurs on the surface of rocks, however, kaolini- other pottery fired at up to 1000 – 1200° salts, most prominently sodium, magnesium, calcium, potassium and strontium cations and te is mixed with organic materials, creating what C) The degradation of materials occurs as a result chloride, sulphate, bromide and bicarbonate ani- are known as white clays. The drainage of these • Ceramics fired at higher temperatures of internal and external factors. The internal fac- ons (LOPEZ - ARCE 2013, 2031-2042). materials and their accumulation at other sites (ceramics fired at above 1000 – 1400°C, tors are the characteristics of the material, of create common clays, containing many impuriti- fire clay; soft - paste, bone china, hard - Conservation of Underwater Archaeological Finds - MANUAL 28 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 29

Over time objects submerged in seawater achie- of living marine organisms. Algae has a bioche- human influences. Human development is ac- In Figure 1. we can see that the sequence of ve equilibrium with the surrounding level of pres- mical effect as its secretions dissolve the sub- companied by an increase in environmental pol- conservation - restoration work does not always sure, in the process of which air is released from strate, while marine organisms such as snails, lution, which results in the formation of acid ra- have to be the same. This depends on the state pores and is replaced by salt water. At the mo- mussels, Cnidaria and polychaetous worms act ins, the accumulation of soot and other impuriti- of the object's preservation, the environment it ment of the object's extraction from the sea and mechanically upon ceramics, boring into them es on cultural property, the pollution of seas by originates from and the type and quantity of de- of the subsequent evaporation of water, the so- and scraping their surfaces (JAKŠIû, BIZJAK waste waters and other effects. Another positions. The order of conservation - restoration lution in the object becomes concentrated. After 2010, 231-245). During their life cycles Crambe frequent source of problems are the unprofessi- interventions may be changed and individual a time, when the solution becomes saturated, crambe sponges, encrusting sponges and the onal and obsolete previous attempts at restorati- steps may be skipped. In the case, for example, the process of salt crystallisation begins. The Cliona sponge erode the surface of objects with on, which have not only failed to slow the pro- of a well - preserved vessel of firm structure, but formation of salt crystals has the same effect as a dense network of tiny holes visible after their cess of deterioration, but have in fact often ac- in a fragmented state, we can immediately un- the process of forming ice crystals when water removal. These surfaces are then fertile ground celerated it. dertake the gluing of fragments without the prior freezes. Their growth during formation causes for colonisation by lithophagous types of mus- consolidation of the material. In some other ca- stress within the structure of the object and the sels such as the date mussel (Litophaga litopha- ses we will proceed in the opposite fashion, and breaking of bonds within the material itself. ga) and Gastrochaena dubia. We also find the THE CONSERVATION AND will undertake all necessary measures to preser- Slower evaporation of moisture from materials calcareous shells of polychaetous worms on the RESTORATION OF CERAMICS ve and strengthen the structure of the object causes salt crystals to break out to the surface - surface of ceramic objects. Bristle worms belong while any one of the following procedures may this is referred to as efflorescence. This pheno- to the genus Polychaeta and form calcareous Conservation - restoration work on ceramic ob- not be required. menon is best observed when we remove a non- shells in the form of a tube around their body. jects can be divided into phases: desalinized object from a moist environment and They are able to penetrate deep into porous ob- 1. Initial documentation, preliminary analysis Conservation - restoration work also depends on allow it to dry slowly in a cold place. We can ob- jects using their jaws or chemically with abrasion 2. Cleaning the object the final location and conditions in which the serve the formation of small white crystals on (JAKŠIû, BIZJAK 2010, 231-245). Accumulati- 3. Desalination object is to be stored (we cannot proceed from the surface similar to fine hairs. This form of salt ons are also created by various types of Cnida- 4. Consolidation the same starting point if the object is to be kept crystallisation causes crumbling and sloughing ria (the best known of which are various corals) 5. Bonding fragments in the open, such as at archaeological parks, or from the object's surface. The speedier evapora- and by green, brown and red algae. 6. Integration in a closed and controlled environment). tion of moisture causes crystals to form inside 7. Nuancing/retouching the object - this is referred to as subflorescence. We should also note the abrasive effect of the 8. Drafting documentation after conducting Any intervention will leave its trace and cause The result is the cracking and fracturing of the sea, which moves particles from the sea bottom restoration work stress to the object. It is, therefore, important to object. The phenomenon of the crystallisation of (sand, pebbles) and in this fashion "sandblasts" note that all interventions on the object must be soluble salts is closely linked with the ambient and wears an object. Objects on the surface of minimal to ensure that our actions do not cause temperature, which determines the relative the seabed are more exposed to abrasive action even greater damage to the object and to pre- humidity and the speed of water evaporation. than those found under the surface. This abrasi- serve the historic value of the object (the pre- on leads to the rounding of the seams along sence, for example, of marine organism accu- The composition and texture achieved with the which fragmentation has occurred and the roun- mulations on the object bear witness to the site firing temperature is a key factor in ding of edges, and finally to the complete loss of at which the object was found, while organic and crystallization decay and hence on the durability the object. other remains tell of the object's use). of these artefacts. Ceramics fired at higher tem- perature have lower surface area and less con- Objects buried underground are exposed to the 1. INITIAL DOCUMENTATION, PRELIMINARY nected porosity, which entails a lower absorption circulation of waterborne minerals, causing the ANALYSIS of soluble salts. Those fired at lower temperatu- accumulation of deposits on objects, most often re display lower total porosity but higher surface calcareous, and possibly containing an Documentation is the beginning and end of res- area rendering them more prone to decay and admixture of sand and soil. Siliceous deposits toration work. The state of the object as it was less durable against weather. These materials may form, while the iron and manganese pre- found in situ or upon arrival at the laboratory usually have more soluble salts and gypsum sent in soil move to the surface and into porositi- must be documented, as must all of the phases subflorescence (LOPEZ - ARCE 2013, 2031- es of the object, where they form brown blemis- of restoration work and the final appearance 2042). hes (CAVARI 2007, 66). post - restoration. We document every pheno- menon visible on the object, fractures, salt efflo- Ceramic archaeological finds from submarine The human effects on ceramics and stone ob- rescence, deformations, alterations to colour, environments are exposed to the accumulation jects are also not negligible. These objects are loss of surface material, deposits accumulated of organic and calcareous deposits (insoluble worn while in use, but are particularly subject to on the surface and all other forms of degradati- salts), and the biochemical and physical effects the consequences of indirect and unintentional Figure 1. The phases of conservation - restoration work on and alteration, and observations concerning (RAVANELLI, GUIDOTTI 2004,139) Conservation of Underwater Archaeological Finds - MANUAL 30 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 31

the object regarding decorations, reliefs and the gin with most delicate techniques, such as brush As the first choice, the mechanical removal of encrustations soluble. The sequestering agent is like. As a preliminary phase documentation has dusting, cleaning with pads soaked in the mil- deposits is always suggested, whenever possib- used to remove insoluble salt deposits, concreti- an investigative role, and helps us discover the dest solutions such as distilled water or a le, from objects extracted from the sea while ons and metal stains by converting the metal problems related to the conservation of the ob- mixture of distilled water and alcohol and/or ace- they are still wet and while the deposits have not into a soluble form that can be rinsed away ject and to find solutions. It may be photograp- tone. If these techniques do not help in remo- become entirely petrified in contact with the air. (PRUNAS, 2012). A solution of tetrasodium ED- hic, written and drawn. Laboratory analysis and ving deposits and if the conservation status of a Following minimal intervention we always start TA salt (pH 11.5) works best for removing calca- radiographic imaging of the object is also under- find allows it, we can apply slightly more aggres- with the most delicate techniques, soft brushes, reous encrustations, which are more soluble in a taken for documentation purposes and to reveal sive cleaning techniques – applying them in a going gradually if necessary and possibly with basic environment (HAMILTON, 1999). It can be problem areas. As an example we can cite the controlled manner and localised on the surface more aggressive techniques such as surgical applied by pads soaked in a 10 to 15% solution successful discovery of iron reinforcements of the deposit. We must bear in mind that chemi- scalpels, ultrasonic chisels and pins, pneumatic of tetrasodium EDTA salt in distilled water, and within ceramic sculptures using radiographic cal cleaning, although very effective and faster chisels, laser, microdrills, micro sandblasting, then mechanically removed. After the chemical imaging. than mechanic cleaning, has some very signifi- pressurizer water jets and by other means. cleaning procedure the object must be cant drawbacks – the process is not always thoroughly rinsed in distilled water to achieve a 2. CLEANING easy to control; the transport of dirty particles in neutral pH level. For the same objective we can pores is possible and it can leave soluble salts also use ionic (cationic/anionic) exchange resins Cleaning is one of the most delicate phases in in the interior of ceramics. (AMBERLITE IR 120 H, AMBERLITE 4400 OH). conservation - restoration work, followed by con- We use them by mixing the resin in the form of solidation, because both are for the most part Removing calcareous and powder with demineralized/distilled water and irreversible, and as such require a good siliceous deposits then applying it using a wooden or plastic stick knowledge and differentiation of foreign materi- (it must not be of metal) on a layer of Japanese als, i.e. accumulations and stains, from what are Calcareous deposits are manifested in the form paper, which protects the ceramic from direct integral parts of the object that require preserva- of the shells of mussels, the skeletal remains of contact with chemical compounds. Their advan- tion, such as patina, irregularities in manufacture corals, and as white spongy clusters that may tage is that they do not penetrate into the and traces of use which should be left untouc- contain admixtures of sand and soil materials in material's porosity and so do not affect the arte- hed on the object. their structure. They are often closely merged to fact. This property is at the same time a disad- the surface and are very hard. They can occur vantage when we need to remove gypsum or Cleaning is done mechanically, mechanico- underground by the deposition of calcium carbo- other salts from a material's deep porosity. They chemically, and chemically. We choose the me- nate transported by water or in an underwater ans based on the type of deposit accumulation, environment as the result of the life cycle of ma- the state of conservation and the material of rine organisms inhabiting the walls of objects. which the object is made. In objects extracted We observe siliceous deposits as low, smooth from the sea we differentiate the calcareous and whitish - transparent accumulations. They are Figure. 3. A ceramic figurine covered by calcareous siliceous deposits of marine organisms, the de- very difficult to remove as they are practically deposits and deposits of marine organisms (Photo: M. posits and infiltration of iron and copper oxides fused with the surface of the object. They are ûurkoviü) and organic deposits (algae, sponges, bacteria). removed mechanically as siliceous bonds are very resistant to chemicals and do not react to When calcareous deposits cannot be removed It is recommended that any cleaning should be- mild acids and bases. by mechanical means we are compelled to use chemical means. Cleaning with the use of che- mical compounds must be strictly controlled, and mild substances must be used that cannot da- mage the physical and chemical structure of the object.

Encrustations of calcium carbonate or calcium sulphate on ceramic material may be treated with EDTA disodium (acid) or tetrasodium (basic) salt. A solution of EDTA in deionised or distilled water is a sequestering or chelating Figure 4. A ceramic amphora on which we see the tra- agent: complexes are formed with some metallic Figure 2. Ceramic jug fouled by algae and the encrustations of marine organisms (Photo: M. ûurkoviü) ces of an iron object that had rested against it in the form ions (Ca++, Mg++, Cu++ and Fe++) making the of iron oxides (Photo: M. ûurkoviü) Conservation of Underwater Archaeological Finds - MANUAL 32 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 33

do not have an effect on thick encrustations sin- the glaze or damage the surface of the ceramic ce they react only with the surface of the encrus- if it is not really well preserved and sound. tation (PRUNAS, 2012). Removing organic deposits Removing iron and copper oxides Organic deposits are created during the decom- Iron and copper oxide stains occur when an position of living organisms or by the sedimenta- oxidised metal object is located near or in con- tion of organic substances. Larger deposits are tact with a ceramic or stone object and metal removed mechanically, while infiltrated deposits oxide particles pass to the structure of the stone can be removed by submerging the object in a or ceramic. Iron and copper oxides are formed 10 to 25% solution of hydrogen peroxide. Smal- by the degradation of metals caused by the ler deposits can be removed by applying a pad combined action of water and air, sometimes soaked in a 10 to 25% solution of hydrogen aided by atmospheric pollution. Oxides penetra- peroxide over affected areas. Washing the ob- te deep into the pores of ceramic materials and ject in a 5% solution of tensioactive hygienic create reddish - brown to black stains in the ca- compound (C 2000) in distilled water with brus- se of iron oxide, and blue - green stains in the hing is recommended for the removal of carbo- case of copper oxides. We often find iron and naceous, fat and oily substances and proteic copper oxide stains on objects extracted from Figure 5. A ceramic jug with orange stains caused by materials. The object can be cleaned with a ten- the sea. They can be cleaned with cotton pads, the infiltration of iron oxides (Photo: M. ûurkoviü) sioactive concentrated preservative (New Des) paper pulp pads or absorbent clays (Sepiolite) based on quaternary ammonium salts, which Figure 7. The fracturing of ceramic caused by the presen- soaked with distilled water. A solution of disodi- porosities. After the use of disodium EDTA salt has an effect on microorganisms and biological ce of soluble salts (Photo: M. ûurkoviü) um EDTA salt in distilled water is more effective, we need to liberally rinse the object in distilled patina. It is used as a solution of 5% preservati- being the most efficient in removing iron and water to achieve a neutral pH level (pH 7). ve in distilled water. It does not need rinsing in The desalination of an artefact from a marine copper oxide stains, as they are more soluble in tap water after the treatment. environment is most efficiently carried out by an acid environment. We use a 15 to 20% soluti- Iron oxides can be removed from objects by su- submerging the object in a bath of clean water on in distilled water on ceramics to remove sta- bmerging them in a 10 to 25% solution of Enzymes (amylase, lipase or a mix of enzymes) that is periodically changed. Tap water is used ins, applied in the form of soaked cotton, paper hydrogen peroxide. The amount of time required may be used on fats, carbohydrates and prote- in the initial phases of desalination, followed by pulp pads or absorbent clays (Sepiolite). When to remove a stain varies from a few seconds to ins to enable them to be washed away. distilled water in subsequent baths. It is impor- applying soaked paper pulp or absorbent clays it several hours. Rinsing is not required after the tant to proceed gradually in order to avoid the is recommended that a layer of Japanese paper use of hydrogen peroxide. We must be aware 3. DESALINIZATION overly rapid release of salts, which could cause be applied to the object followed by the pulp/clay that bubbles produced by the reaction of additional damage to the object. The to prevent the penetration of the material into hydrogen peroxide with the stains can detach We have already touched upon the problem of conductivity of the water is measured before and soluble salts and moisture in porous materials in after every change of water with a conductivity previous chapters, in this case affecting cera- meter and/or potentiometric titration as an indi- mics and stone. Soluble salts are most often cator of the quantity of salts that have been sec- present in objects extracted from the sea, but reted. When the quantity of salts (conductivity) we also find them in objects that were found in has been reduced to a minimum constant value the open or underground in seaboard areas. the process of desalination can be completed, They are removed by the desalination process. i.e. the object can be taken out of the bath and Desalination is defined as the maximum possib- allowed to dry in a shaded location. Care should le reduction of the salt content of a material ef- be taken that the object is not exposed to signifi- fected through its extraction. Extraction is under- cant oscillations in temperature during drying. taken to achieve three principal objectives: mini- mise the deterioration of the material caused by There are a number of methods of desalination the process of crystallisation/dissolution of solu- by soaking: ble salts, prevent future deterioration and avoid • Desalination in closed baths with frequent the alteration of subsequent restoration proce- changes of water and measurements. Figure 6. Large Iznik plate covered with iron oxides before and after conservation - restoration treatment (Photo: M. dures such as consolidation or integration • Desalination in baths with pumps that im- ûurkoviü) (ZORNOZA - INDART, 2009, 2031-2042). prove water circulation. This prevents the Conservation of Underwater Archaeological Finds - MANUAL 34 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 35

occurrence of salty pockets in hard to rea- terior and the outer surface of the material. The plied on wet artefacts, as they are aqueous dis- the object as a single logical entity. ch places under and inside the object and choice of consolidant is based on its penetration persions. They can be applied in various per- thereby facilitates and accelerates the characteristics, permeability to water vapour, the centages by immersion, spraying, coating and The phase of preliminary bonding in which we process of salt secretion. Water final appearance it imparts and the heightened under a vacuum. attempt to locate the exact position of every fra- conductivity measuring is carried out at mechanical durability it imparts to the material gment involves joining the fragments with paper every change of water. after treatment (BORGIOLI 2002, 8). Polyvinyl acetates – are swollen by water, beco- adhesive tape prior to final gluing. Sensitive sur- • Desalination in flowing water baths. This ming opaque white but reverting to a clear film faces, such as glazing and painted decorations is the most effective, but also the most The consolidant should always penetrate as de- on drying. Of all the polymers available for con- should be specially protected to avoid breaking expensive procedure. The large quantities ep as possible into the pores of the material in servators, PVAC has been shown to be one of off and "tearing" the surface with paper adhesive of tap and distilled water used presents a order to avoid creating a belt of discontinuity the most stable to light ageing (HORIE, 1987). tape. Permanent bonding is performed after all problem. Conductivity measurements are between treated and untreated sections. The Mowilith 50 can be used both as a consolidant fragments have been precisely located. made during the entire process. existence of a discontinuity belt causes stress and as glue if prepared in different percentages. In the case of low - fired or extremely large ob- between the two sections, and leads to structu- Mowilith 50 is readily soluble in many solvents Reversible adhesives that solidify by the evapo- jects it may be preferable to undertake desalina- ral damage. A very diluted solution with small such as acetone, esters, ketones, aromatic ration of the solvents in which they are dissolved tion using packs. Packs of paper pulp, Sepilote molecules (ethyl silicate is noteworthy in this hydrocarbons and the lower alcohols (the latter and that can be dissolved again are used for or Laponite RD soaked with distilled water are respect) is used with the aim of deeper penetra- require the addition of a low level of water as a bonding. Stronger glues with greater adhesive used to extract soluble salt from pores. Their tion. Objects with greater porosity can be impre- co-solvent). After application it may slightly dar- strength should be used when gluing fragments effect is much slower than the soaking methods gnated with more viscous solutions in very low ken the original colour of the ceramic. It can be of large ceramic objects. In these cases we are as less water is employed. concentrations. applied in various percentages by immersion, compelled to use non-reversible two-component spraying, coating and under a vacuum. epoxies of exceptional firmness and great adhe-

The optimum consolidation agent should sive strength. Epoxies can be used in the resto- be reversible in solvents enabling easy ESTEL 1000 is a ready - to - use consolidant ration of porcelain for gluing and as filling materi- repeated interventions on the object if based on ethyl silicate and polysiloxane oligo- al for integrations. they become necessary in the future. So- mers in white spirit D40 solution. It can be appli- lutions and emulsions of organic and inor- ed by immersion, brushing or spraying until satu- Mecosan L-TR is a solvent based artificial resin ganic compounds are used for the conso- ration is achieved. The curing of the consolidant adhesive. Adherences carried out with Mecosan lidation of materials: acrylic resins and is completed after about four weeks at an ambi- L-TR are resistant to water, oils, grease, gasoli- micro emulsions, polyvinyl acetates, ethyl ent temperature of 20°C and a relative humidity ne and alcohol. After drying it shows a translu- silicate and others. They are applied in of 40-50%. cent adhesive film. various percentages by immersion, spraying, coating and under a vacuum. Archaeocoll is a special adhesive for archaeolo- gical ceramics and other porous materials. It Acrylic resins – Paraloid B72 is a 100% consists of pure cellulose nitrate. Its speciality is Figure 8. Seeking the appropriate fragments (Photo: M. ûurkoviü) acrylic resin based on ethyl methacrylate the total absence of any softening agents, so a with excellent properties in terms of har- maximum of aging stability is obtained. The vo- 4. CONSOLIDATION dness, brightness and adhesion to a substrate. latile solvents (ethyl acetate and acetone) are Paraloid B72 is soluble in ketones, esters, aro- non - toxic. Objects to be joined must be dry and The consolidation of materials is carried out only matic and chlorinated hydrocarbons, and can be dust free. The adhesive can be removed any if necessary, i.e. when the surface and structure applied in various percentages by immersion, time by solvents such as acetone, ethyl acetate of an object are damaged, powdery and frangib- spraying, coating and under a vacuum. or propylene glycolmethylester. le or in the case of glaze falling off a ceramic object. Consolidation consists of the impregnati- Acrylic emulsions – Acril 33 (ex Primal) is a Mowital B 60 HH is a vinyl butyral polymer Figure 9. The process of bonding fragments (M. ûurkoviü) on of material that has lost its structural soun- 100% pure acrylic resin in aqueous dispersion chieÀy used in archaeological restoration for dness using liquid solutions that, once they have characterized by excellent resistance to atmosp- bonding and consolidating ceramics. Mowital B penetrated into the structure of the object, heric agents and chemical stability. ACRIL ME is 5. BONDING 60HH answers very well to the following proper- solidify, thereby strengthening the walls of the a micro acrylic emulsion characterized by the ties: reversibility, resistance to ageing, pores. The optimum protective agent should reduced size of its particles (around 50 microns). Objects are often found in a fragmented state. transparency, setting rapidity and minimum retard or stop the absorption of water into the This causes a low viscosity and a greater Fragments are bonded to achieve the stability shrinkage. It is diluted in alcohol with percenta- material without creating a barrier that would capacity of penetration into porous substrata and integrity of the object, which will allow a nor- ges varying according to use and is reversible in prevent the exchange of gases between the in- than normal acrylic emulsions. Both can be ap- mal observer or scientist to read and understand alcohol and acetone. Conservation of Underwater Archaeological Finds - MANUAL 36 ûurkoviü M.: The Conservation and Restoration of Ceramics and Pottery 37

with sandpaper of various granulations or a mic- rodrill after drying. Plaster is easily reversible as it softens with the addition of water, and is then easily removed mechanically.

Polyfilla is an inert cellulose based filler. It is usually used for filling smaller gaps because of its lack of firmness.In some restoration laborato- ries we find the use of wax mixtures for model- ling integrations. Integrant I 76 is a mixture of virgin beeswax, colophony, paraffin wax, dental plaster and zinc oxide. Each of the mentioned waxes must be melted at the required tempera- Figure 11. Fabricating an integration on a potter's wheel (Photo: M. Mustaþek) ture and then mixed together. The remaining ingredients are then added to the liquid mixture excellent hardness and ¿delity of detail repro- as powders. It is applied to the object while Figure 10. Gluing ceramics (Photo: M. ûurkoviü) ductions. It has a low expansion ratio when har- warm, and can be refinished and remodelled dening (0.05%). Alabaster plaster is a natural with a heated instrument. This type of integrant Polyvinyl acetate – PVA – K 40 and K60 is a ted at the site (underwater or underground) or as plaster with excellent features, used to make endures the higher temperatures that often oc- thermoplastic resin based on polyvinyl acetate a result of unskilful handling and extraction from moulds and, generally for artistic work cur in showcases, and can be detached from the homopolymers soluble in alcohols, esters, keto- the site. Intervention on an object is required (expansion: 0.15%). They are both good integ- ceramic body. nes, toluene and chlorinated hydrocarbons, and when the stability and readability, i.e. its physical rants in restoration because of the minimal is particularly suitable for heat - sizing/gluing of and aesthetic integrity, have been compromised. expansion ratio and physical appearance and 7. NUANCING / RETOUCHING archaeological ¿nds and ceramics. Objects are reconstructed only when all of the characteristics similar to ceramic. Ceramic frag- elements required for reconstruction are availab- ments can be protected from eventual salt relea- Retouching has a predominantly aesthetic roleit Paraloid B 72 and Mowilith can also be used as le. Integrations can be made directly on the ob- se from the plaster by coating/sealing the joints does not prevent or retard the object's deteriora- glue when dissolved with acetone in a higher ject or indirectly, fitting the integrated part in the with a consolidant applied by brush. The tion, but rather restores its aesthetic integrity percentage. original after it’s refinished. The direct method is external walls of the ceramic can be protected and its aesthetic value. The goal of retouching is more invasive than the indirect method as there by liquid latex, which can be peeled away after to nuance integrated parts of fragmented objects Cyanoacrylate glues (Supper Attack, Super is a greater possibility of damaging the object integration is finished. Moulds of clay, plasticine, and to assimilate them, in a greater or lesser Bond and others) are used for immediate and during the process of integration. In the indirect wax leaves, adhesive tape, silicon rubber putties extent, with the surrounding material. Retouc- only temporary bonding because they are brittle method a cast is made in order to replace the and pastes, and various other materials are ma- hing should be limited to the integrated part, and do not have a long lifetime. missing section. After the integrated part has de as a support to integration. Silicone moulds avoiding the overpassing of colour along the been treated it is inserted into the original part. are used to make casts for more elaborate deco- edges of the original material. There are several Epoxy resins (Araldite 2020, HXTAL NYL-1, This method is less invasive to the original ob- rations. When a large part of a (ceramic) vessel approaches to how restored objects should be EPO 121 and others) have the quality of great ject but it takes more time and several attempts is missing, integrations may be made of plaster retouched. adhesion and strength but are difficult to rever- are required to effect the successful insertion of on a potter's wheel, modelled with the aid of the se, which makes them a second choice in con- the integrated part into the original one. Integra- internal and external casts of the object. Plas- Archaeological objects should be retouched in a servation. We often use them for gluing porcela- tions are made from materials that should, by ters can be pigmented by adding natural pig- in and glass objects because of the similar their physical characteristics and appearance, ments to plaster before mixing it with water. Se- physical characteristics they obtain after the cu- be as similar as possible to the original and be veral samples of pigmented plaster must be ma- ring process and refinishing (hard and shiny sur- chemically stable. When integrating ceramics we de before deciding on the right mixture because face). Bonding porcelain objects is done in the can use different materials: different type of pla- the real colour of the pigmented plaster can only same manner as described for glass (pages 43- sters (dental, alabaster), cellulose strengthened be seen after it cures and dries. We can mix the 44). binders (polyfilla), wax mixtures such as integ- plaster with a 5% water based consolidant (for rant I 76, synthetic clays (Glinamol, Das) or ot- example Acril 33) to improve its hardness and 6. INTEGRATION hers. inertness.

After the gluing procedure fragmented objects Dental plaster is a natural plaster with all- Integrations are worked with files, scrapers and often lack material/fragments lost while deposi- purpose possibilities in modelling techniques, other hand tools while still wet, and are polished Figure 12. The process of filling joints (Photo: M. ûurkoviü) Conservation of Underwater Archaeological Finds - MANUAL 38 ûurkoviü M.: The Conservation and Restoration of Glass 39 way that keeps the integration visually distingui- object is photographed from all angles, and a V. The Conservation and Restoration of Glass shable from the original part. This is achieved by written description of its final state is drafted. colouring the integrated surface in a colour that Sketched documentation and recommendations is two or three shades lighter, but very similar to Martina ûurkoviü for the manufacture of glass vary and can be for the preservation of the object in future stora- the tone of the original. In some cases the pat- [email protected] exchanged for other ingredients. By its composi- terns and nuances present on the object can be ge and depositing are appended. Also appen- tion we divide glass into these groups: soda-lime reproduced on the integrated surfaces, but ded to this documentation are the eventual re- glass, crystal glass (lead), borosilicate glass, always in a lighter tone. The application of sults of laboratory analysis related to the object. INTRODUCTION aluminosilicate glass and silicate glass (quartz) "invisible" retouching is frequent when dealing (LEMAJIý 2001, 2). The quantity of these added with antiquary objects, where every shape of Glass is an amorphous substance that is crea- ingredients will determine the character and decoration, relief and any visual effect of the ted by the cooling and solidification of the melt quality of the glass. In general, glass durability original parts of the object are faithfully reprodu- without crystallisation. We differentiate natural decreases for increasing amounts of network ced. This kind of retouching is not recommen- glass (volcanic) from artificial glass (technical). modifiers. ded as it can easily become false. All materials Natural glass is created in volcanic eruptions Glass is processed at high temperatures. A solid used in retouching must be reversible. The most (obsidian) or when lightning strikes sand block of glass is placed in a furnace where it is frequently used are water - based acrylic colours (fulgurite) in cases where the melted stone/sand melted and then placed on the tip of a pipe. easily soluble in acetone, water - soluble tempe- cools quickly enough that there is no Blowing through the pipe creates a bubble that ra and powdered pigments mixed with acrylic crystallisation. Humans first manufactured artifi- is then, in further processing, shaped into a bot- emulsions. They are applied with a brush, spon- cial glass about 3000 BC as a glaze to coat ves- tle or vase, and then removed from the pipe. ge, brush-spattered, airbrush and other met- sels and brick. The manufacture of independent Throughout the entire process of manufacturing, hods. After drying, the coloured areas can be glass objects began around 1500 BC glass objects need to be heated, i.e. the glass protected with a matte protective coating (acrylic (RODGERS 2004, 145-146). Glass is also pre- mass must be melted by periodically returning it emulsion, matte sprays) or a glossy coating in sent in the form of opaque enamel on metal sur- to the furnace. There is also a method of sha- the case of glazed ceramic vessels (glossy faces, and as Egyptian faience. Glass is ping glass with the aid of moulds where a hea- lacquer, glossy sprays). These may be applied artificially coloured by the addition of metal ted glass mass on a pipe is introduced to a by brush or spraying. oxides of manganese, cobalt, chrome, copper, wooden mould, and thereby modelled by being iron and others in the blend prior to melting. De- Figure 14. A pot after conservation - restoration treatment blown into various shapes. 8. DRAFTING POST - RESTORATION (Photo: M. ûurkoviü) colourisers were also used, usually Mn which DOCUMENTATION produces a complementary colour to neutralize the blue/green tone produced by Fe, with the Comprehensive written and pictorial (sketch and result of a virtually colourless glass. photo) documentation should be drafted as the final step in conservation - restoration work. This Glass made only of silicate crystals (SiO4) is the most solid and resistant to acids and bases. Be- documentation must contain all data gathered cause of its very high melting point (about prior to, during and after restoration work. The 1710), glass had to be made with a lower mel- initial situation of the object as found is docu- ting point, as it was technically very difficult to mented, with photographic and written records produce glass from pure silicate. Thus to silicate of its state of conservation, the presence or per- (SiO4), as the chief ingredient, network modifiers haps absence/lack of decoration, the presence (Na+, K+, Li+) have been added to break the of deposits and infiltrations, traces of previous bridges between the network formers (Si) and Figure 1. Matted glass beads, beads with surface irides- oxygen, thereby lowering the melting point of the restoration attempts, the object's dimensions cence (Photo: M. ûurkoviü) glass. This breakdown of the network at several and number of fragments, the origin and period points weakens it and affects the properties of of its creation and all other observations related the glass. Network stabilizers (Ca2+, Mg2+) are DEGRADATION OF GLASS to the object. Materials and procedures used on added to give strength to the glass structure. the object during restoration work are recorded, They also break the bridges between network Glass is a material that was created from a formers (SiO ) and oxygen but link at the stron- as are the results of their application. When con- 4 crystalline form using high temperatures gest bonds because of their ionic potential and servation - restoration work is completed the (energy), and has the characteristic of becoming their smaller dimensions. These basic materials

Conservation of Underwater Archaeological Finds - MANUAL 40 ûurkoviü M.: The Conservation and Restoration of Glass 41

carbon dioxide and form sodium and potassium carbonates. The carbonates thus formed conti- nue to absorb water from the environment, per- petuating the reaction and the deterioration of the glass. As a result we have a weakened structure consisting only of silica (SiO4). The following step in the degradation of glass is the dissolution and decomposition of this weakened structure.

Dramatic physical damage can occur to objects extracted from the sea during the drying process Figure 2. An eroded glass surface, magnification 50 x Figure 3. Micro fractures, magnification 50 x (Photo: M. as a result of the activity of soluble salts. In the ûurkoviü) process of evaporation soluble salts in the struc- (Photo: M. ûurkoviü) Figure 6. Glass iridescence (Photo: A. Jeliü) ture or on the surface will crystallise and cause crystalline again, to return to the state of lower today also consider depositions that should be the object to fracture. energy. This process is a very slow but can be removed (DAVIDSON 1989, 171-172). effect is aceved by physical means, by the abra- stimulated by various factors. The degradation sive action of sand and other substances in the of glass is caused by three factors: as a result of The greatest chemical damage to glass is cau- underwater environment. Poorly preserved glass physical damage, changes to the surface sed by water and water solutions (sea). In con- may survive in the form of a chalky silica gel, (deposits) and chemical damage. Because of its tact with water chemical changes are initiated on having lost the characteristics of glass – clarity brittle nature glass is subject to damage caused the surface of glass, a process that then conti- and transparency, and is as such very difficult to by mechanical activity. We find the causes of nues within the structure of the glass material identify as glass. Discolouration occurs when physical damage in production defects, impact (CRONYN 1990, 131). Chemical degradation metal oxides are leached from glass, when me- or falls, thermal shock, abrasion or previous at- occurs as a result of weak chemical bonds tal oxides in the glass are oxidised, or by the tempts at restoration (DAVIDSON 1989, 169- within the structure of glass between the base of absorption of metal oxides from the environ- 170). silica and added substances, i.e. the modifiers ment. Spontaneous cracking is frequent in the and stabilisers. presence of a damaged hydrated glass surface. Foreign substances may also accumulate on the Cracking occurs when a hydrated surface is re- surface of the object or inside glass vessels. Contact with water leads to the leaching of posi- Figure 5. The flaking of a glass surface (Photo: M. ûurko- duced in volume as a result of drying. Fractures Deposits are created by the use of the object, tive K+ and Na+ ions, followed by Ca+ and Mg+ viü) can occur on the surface of the glass, but may the deposition of material when buried or depo- ions. They react with water to form hydroxides. The visible symptoms of glass degradation are: also affect deeper layers. These surfaces are sited in a marine environment, the deposition of Positive hydrogen ions replace the positive ions rainbow lustre (iridescence), a matte surface even more sensitive to external factors, i.e. the products of metal corrosion, atmospheric of the modifiers that have leached out, which with the formation of flakes, the loss of the glass humidity, and as such subject to further degra- pollution or from an excess of material used in a hydrates the glass. After drying they react with nature of the object, discoloration, incrustation dation. previous restoration procedure. In the case of and deposits and spontaneous fracturing. deposits created by the use of the object these are the remains of cremation, food, drink, medi- The presence of rainbow colours on the surface THE CONSERVATION AND cations, paints and the like. Soil, calcareous, (iridescence) occurs as a result of a delaminated RESTORATION OF GLASS siliceous and black sulphide stains on the object glass surface caused by its chemical degradati- may occur during interment. If a glass object is on. Because of the uneven and delaminated Conservation - restoration work on glass objects located near a metal object there may be a de- surface, light is reflected at different angles, cau- can be divided into phases: position of iron oxides. On glass objects submer- sing it to shine in the colours of the rainbow. 1. Initial documentation, preliminary analysis ged in a marine environment we find calcareous This lustre can only be observed when the ob- 2. Cleaning the object and siliceous deposits composed of the skeletal ject is completely dry, i.e. when the water 3. Desalination remains of marine organisms, deposits of algae between layers is dried out. Thin layers of deg- 4. Consolidation and of other living marine organisms, and the raded glass flake off upon drying, damaging the 5. Bonding fragments already mentioned iron oxides. Previously resto- surface up to the level of complete decay. The 6. Integration red objects may have the residue of adhesives, Figure 4. A scratched and eroded surface, magnification damaged surface is uneven, matte and given to 7. Drafting documentation after conducting adhesive tape and fillers on them, which we 50 x (Photo: M. ûurkoviü) sloughing and flaking. A similar matte surface restoration work

Conservation of Underwater Archaeological Finds - MANUAL 42 ûurkoviü M.: The Conservation and Restoration of Glass 43

As in the case of the restoration of ceramics and cleaning, and leave the deposits on the object, described in the case of ceramics with EDTA ted by exchanging the water (also referred to as stone, the sequence of restoration procedures than to go ahead with removal that could dama- salts and ionic exchange resins. dehydration) by submerging the object in anot- may vary depending on the level of an object's ge a degraded surface or the object as a whole. her solvent (acetone, alcohol) following by im- preservation and the conditions in which it was In the case of highly damaged glass the priority 3. DESALINATION mersion in a consolidant soluble in the same deposited. is to consolidate the material, and then to under- solvent or with a water - based consolidant. Sili- take mechanical cleaning. Deposits can be re- Glass objects extracted from a marine environ- cone oil is a consolidant applied to objects 1. INITIAL DOCUMENTATION, PRELIMINARY moved with a soft brush, scalpel and cotton ment must pass through the process of desali- dehydrated in acetone. It is applied under pres- ANALYSIS swabs soaked in solvents while the object is still nation to remove soluble salts. Desalination is sure to improve the penetration of the consoli- wet. Painted decorations, colours and gilding on conducted in the same fashion as with ceramics, dant and to facilitate the evaporation of acetone. Photographic and written documentation of the glass surfaces should be protected with a coa- by submerging the object in a tap water bath, The same method can be used to consolidate state of an object as found must be made before ting of consolidant - they must not by any means later in distilled water, with regular changing of with solutions of acrylic and polyvinyl resins. Dry the start of restoration work. The remains of co- be cleaned using water. the water. The desalination process is comple- objects can be consolidated with the same subs- lour, gilding, engraving or a painted surface of- ted when measurement of the water's tances by coating, spraying, immersion or under ten adhere to the layer of deposits. If a decorati- conductivity establishes a minimum constant pressure. The most frequently used consolidant on is not identified there is a significant quantity of salts (i.e. the lack thereof). The ob- for glass is still acrylic resin Paraloid B72. possibility that the cleaning process will ject is then ready for air - drying and/or to under- unintentionally remove it together with the accu- go consolidation only in special cases when this 5. BONDING mulated deposits or damage it. We can use is indispensable. radiography or filming under UV light to reveal Bonding fragments secures the object's stability decorations on the surface. 4. CONSOLIDATION and aesthetic integrity. Materials used for gluing must possess the characteristics of 2. CLEANING Consolidation is conducted only when indispen- transparency, good adhesion, and reversibility sable, in the event of the sloughing, flaking and and must not be damaging to the object. Paralo- When cleaning glass it is important to know that crumbling of the surface. It should always been id B72 acrylic resin has been used for this pur- cleaning implies the removal of soil and deposits kept in mind that consolidation is an only partly pose but does not have a long lifetime and lacks accumulated on the surface, but not the removal reversible procedure and that it is better to avoid satisfactory adhesive strength. Epoxide resins of the products of glass degradation. Doing so Figure 8. Glass neck covered with marine organism it if there is not an unequivocal need to underta- such as Araldite 2020 and HXTAL NYL-1 have would be considered the destruction of a part of deposits (Photo: M. ûurkoviü) ke it. Removing consolidants is only partly possi- successfully replaced it. They are very transpa- the original object, because the removal of these ble because there is a decline in reversibility, rent and have physical characteristic similar to damaged surface areas may significantly and Preserved archaeological glass may be treated and because of the damage that may be caused glass. detrimentally affect the original dimensions of with mild chemical cleaning. Objects extracted by the use of solvents that would engender the the object. The selection of material that shall be from muddy sites may be cleaned with tap repeated wetting and drying of the object. Con- Prior to gluing, the object must be cleaned of used in cleaning depends on the level of preser- water, distilled water or other solvents before the solidation is carried out to preserve and improve dust to ensure the better adhesion of the glue. vation of the glass, decorations present on the object dries and is consolidated. The best choi- the sturdiness of the object and to restore the Fragments may initially be joined with very small surface and on the types of deposits we intend ce would be a mixture of solvents with different transparency a glass object has lost by the deg- strips of adhesive tape. If the surface of the to remove. It is always better to not undertake evaporation points, such as a mix of acetone, radation of its surface. A consolidant penetrates glass has been well preserved, the strips are alcohol and water (1:1:1). An oily film on the sur- into the structure of the object and fills minute replaced by metal clips that are applied to the face of the object can be cleaned with a 25% cracks, smoothing out unevenness and impar- outer wall as bridges linking two fragments, and solution of hydrogen peroxide in water. ting transparency. It should be noted that it is are affixed with little drops of cyanoacrylate glue not enough to consolidate only the damaged (Super Attack) only to the places where clips Deposits of metal oxides can be removed surface of the glass object, but rather that the touch the surface of glass. mechanically or by the controlled use of chemi- consolidant must penetrate deep into the struc- cals in the same manner as in the case of cera- ture and bond with the preserved glass core. An These small bridges enable the application of mics (page 32). Metal oxides are often firmly object that appears dry may contain water mole- liquid glue along the whole length of the joint. bonded with the damaged glass surface, and as cules within its structure. Drying this kind of ob- Liquid glue enters the joints by capillary action. such it is sometimes better not to remove them. ject, or a wet object, by heating or under a vacu- Therefore it is important that the fragments have um, leads to the dehydration of the hydrated been joined as well as possible and that there Calcareous and marine organism deposits can surface, shrinkage and the loss of the material. are no pores between them, so that the glue can be mechanically removed with a scalpel while be absorbed into the joints by capillary action. Figure 7. A test cleaning of calcite deposits (Photo: M. the object is wet. Chemical cleaning is done as A degraded wet glass object can be consolida- For this purpose the most frequently used ûurkoviü)

Conservation of Underwater Archaeological Finds - MANUAL 44 ûurkoviü M.: The Conservation and Restoration of Glass 45

fragments are present but there is a model of the warm putty onto the object. We can put some original appearance. Partial reconstruction is car- two - component vinyl polysiloxane impression ried out on objects where there is insufficient in- material around the leaf to seal the borders. We formation about the original appearance. Recon- then apply the outer leaf, affixing it in the same struction then has the role of linking fragments manner. We then cut out two holes – one throu- and ensuring stability. gh which the resin is poured, the other enabling bubbles of air to escape from the cast (in order In both cases to fabricate integrations we use the to not be captured in the resin). At these holes same epoxy resins as are used for bonding we install two wax cylinders, affixing them with (Araldite 2020, HXTAL) because of the excellent melted wax. When the cast is completely sealed characteristics they demonstrate after drying. and its functionality has been checked (simply Figure 9. Joining fragments with adhesive tape (Photo: M. These are fluid resins that are easily toned and by blowing through the cylinder) we can start ûurkoviü) upon drying becoming transparent masses very pouring the resin into it. Once the resin has fully similar to glass. The negative side of these epoxy hardened, the cast may be removed, and we epoxide glues are Araldit 2020 and HXTAL NYL resins are their long hardening times, which re- can undertake the finishing of the integration. 1. Araldit 2020 is more economical in terms of sults in the resin flowing from the place it was The integration must be finished using abrasive Figure 12. Integration using epoxy resin with the aid of a cost and dries quicker than HXTAL glue (HXTAL intended to dry in and a reduced possibility of paper or a microdrill, exercising caution in order silicone mould (Photo: M. ûurkoviü) has a very long setting time – an entire week is manoeuvring the resin when fabricating an integ- to avoid damaging the surface of glass. required for complete curing) but tends to yellow ration. into a shape that effectively covers the gap (in more readily than HXTAL. Any excess glue can the shape of the gap, but a little wider to extend be removed using cotton swabs soaked in aceto- Integration can be done directly, by filling the over the edges). The cast is attached to the in- ne and well drained in order to prevent any gaps directly on the object, or indirectly when ner side of the object using a compatible glue for excess acetone from affecting the speed of resin the missing part is fabricated separately and silicon casts, while the edges of the cast are well solidification. After the glue has completely dried, then joined to the artefact. Pigment is added to sealed using impression material in order to pre- the metal clips can be removed mechanically or one component of a quantity of two - component vent the loss of resin through holes. Two holes by softening their bonds with the aid of cotton glue that will be, once mixed, sufficient for all are made in the front cast using a needle, one swabs soaked in acetone. required integrations. for pouring in the resin, the other for the outflow of excess resin. The holes have to be placed in 6. INTEGRATION / GAP FILLING Powdered pigments are used as colorants, first specific positions in order to allow the resin to dissolved in a small quantity of solvent (Microlith enter the mould at a lower point and exit at a Integrating a glued glass object restores its pigments for glass) or as already prepared glass higher point in order to evacuate all the air insi- stability and aesthetic value. Integration is possi- paint (Vitrail by Lefranc & Bourgeois, Pebeo or de and avoid the creation of bubbles (FERUCCI, ble only when there is sufficient data on the ob- others). Figure 11. Toning epoxy resin (Photo: M. ûurkoviü) 2012). The front section is glued to the object as ject and its original appearance. Complete and Integrations done using silicone casts are more described for the inner part; then drinking straws partial reconstruction is possible. Complete re- In the direct method, a cast is made directly on precise, and there is no need for finishing. The are applied at the holes to serve for pouring in construction is done with objects when most of the object into which liquid resin has been pou- drawback of dental silicone is its high price in and out. The straws are glued using the original parts are present and some gaps red. For the successful fabrication of an integra- comparison with wax leaves. We make the sili- cyanoacrylate glue and then permanently affixed need to be filled, or when only a small part of the tion, we need a solid preparatory phase invol- con cast by putting two separate layers of silico- using the same impression material. The validity ving the fabrication of appropriate moulds. Casts ne on the inner and outer surfaces of the glass of the cast can be tested by blowing through the may be done using wax leaves or dental silico- over an area the same size and shape of the straws (air must be heard coming out on the ne. missing part (we immediately produce the two other side). Epoxy resin is poured into the lower walls of the mould – inner and outer). The first straw until resin begins to pour out through the For the wax leaf method, the leaves have been layer is a two - component vinyl polysiloxane upper straw. cut with a scalpel in the shape that will cover the impression material, which is laid out thinly, so cavity – one from the inside, the other from the that it authentically reproduces even the tiniest These methods (silicone and wax) can be com- outside. details of the surface. While it is not completely bined when, for example, the missing portion, or dried out, we apply the other layer of compatible a decorated surface, does not permit to use the The leaves can be modelled and curved using a silicone putty onto it, which serves to give har- silicone. It is possible then to make the walls Figure 10. Joining fragments with metal clips, detail (Photo hot air blower. First we place the leaf on the in- dness to the cast. After drying, the silicone wall with wax and seal them with silicone and add from Museum of Ancient Glass in Zadar) ner side, creating a good seal by pressing the is set apart from the glass and cut by scissors the straws.

Conservation of Underwater Archaeological Finds - MANUAL 46 Joziü A.: The Conservation and Restoration of Metal Finds 47 epoxy resin sheets can then be easily adapted VI. The Conservation and Restoration of Metal to the form of the artefact. Finds The other indirect method is done by reprodu- cing and modelled the missing part in plaster to Antonija Joziü can slow it as much as possible (KLARIû 1998, achieve the desired shape. It is then removed [email protected] 53). from the artefact and a silicone cast made from

it. Epoxy resin is then poured into the silicone The proper choice of materials, tools and met- cast and, once hardened, removed from the cast INTRODUCTION hods with which to treat metal objects depends and then integrated and glued into place. This greatly - besides on the analysis of damage and method presents the danger of damaging the Throughout history what are now metal archaeo- the state of the object - on a knowledge of the artefact during the modelling of the plaster. logical finds have been manufactured for the nature of the products of the corrosion of a given

most part from iron, copper, silver, gold, lead metal, and thereby of the characteristics of the 7. DRAFTING POST - RESTORATION and tin. These metals, with the exception of metal from which the object is made. DOCUMENTATION gold, rarely occur in nature as elements, and are found for the most part in the form of ores that As is described in the previous chapter on the are their stable state. As a result, from the mo- restoration and conservation of ceramic and sto- ment of their production, the cited metals and THE CHARACTERISTICS AND ne material, comprehensive written and pictorial their alloys tend to return to their initial state, MECHANISMS OF THE CORROSION (sketch and photo) documentation should be reacting with the environment and initiating the drafted as the final step in conservation - resto- process of corrosion, converting them into stable OF BASIC METALS IN Figure 13. Integrating small imperfections using the ration work. Restored glass objects should be compounds. ARCHAEOLOGY indirect method (Photo: M. ûurkoviü) stored in constant conditions, away from direct In the case of ovoid closed forms (balsamarium, sources of heat. The corrosion of metal is a spontaneous pro- The metals can be graded in reactivity from bottles, vessels) for the inner mould we can use cess of unintentional destruction caused by highly corrodible (base) to unreactive (noble). a balloon inflated from the inside of the object. physical, chemical and biological agents. It can be classified on the basis of the environment in IRON > TIN > LEAD > COPPER > SILVER > GOLD In the indirect method a sheet of epoxy resin is which it occurs, based on the appearance of the Most base Most noble cast that is of the same thickness as the glass corrosive attack and based on the mechanism of wall at the missing section. A form identical to its action. When conserving and restoring metal The corrosion of metal products in an the gap/missing section is then cut out and objects we must, therefore, bear in mind that underwater environment (seas, lakes, rivers, affixed to the original with adhesive tape. Epoxy metal corrosion is a spontaneous mineralisation swamps and the like) occurs in an electrolyte resin is poured in at the joint of the original glass and that the process is almost impossible to and is as such, by the mechanism of its action, and fabricated epoxy resin plate to glue in the stop entirely, but that, with proper protection, we electrochemical, which means that there is integration. This method is very effective with thin - walled glass artefacts, as the thinly poured

Figure 15. An artefact after conservation - restoration work (Photo: M.ûurkoviü)

Figure 1. A schematic depiction of the electrochemical mechanisms of corrosion in an underwater environment (Drawing: Figure 14. A partially reconstructed artefact A. Joziü) (Photo: M. ûurkoviü)

Conservation of Underwater Archaeological Finds - MANUAL 48 Joziü A.: The Conservation and Restoration of Metal Finds 49

initially an oxidation of an atom of metal into a nism, which is the first phase of free cation, which only by secondary processes autocatalytic pitting corrosion. produces a molecule compound that is a corrosi- on product (HAMILTON 1999, File 9). The che- mical composition of corrosion products will de- IRON AND ITS ALLOYS pend on the reactants present in the environ- Iron is the most important technical metal. In its ment. The products may be laid down as amor- pure form it is a white, brilliant and relatively soft phous powders but it is more common for metal. In nature it is very widespread (about 5% crystals to be formed. of the Earth's crust), and occurs for the most Figure 2a. Iron legionary spear, Lenovac site, prior to Figure 2b. Iron legionary spear, Lenovac site, post- intervention (Photo: A. Joziü) intervention (Photo: A. Joziü) Depending on the solubility of the corrosion for- part as oxide (magnetite Fe3O4, haematite Fe2O3, limonite 2Fe2O3×H2O), carbonate med, products can be developed in two situati- chloride, which completely destroys the metal vironments, besides having accumulations of ons: (siderite FeCO3), siliceous and sulphide ores. It is rarely used as a pure metal, and it is most core. It should be noted that a strong corrosive corrosion products, are almost always also co- • Active corrosion - the metal forms soluble layer occurs on objects with inserts and applica- vered in incrustations characteristic of the envi- products that move away from the metal often alloyed with other elements (FILIPOVIû; LIPANOVIû 1995, 1024-1036). Archaeological tions of metal that are nobler than iron. A whole ronment from which they were extracted (rock, into the surrounding environment. This range of corrosion processes occur during corro- sand, molluscs, skeletal remains of dead marine usually occurs in very acid or extremely iron is in most cases wrought iron (up to 0.35% carbon), and iron archaeological finds at sion in a fluid medium, i.e. sea or fresh water - organisms and the like) (HAMILTON 1999, File alkaline environments when all trace of the presence of carbonic acids creates carbona- 9). the metal is lost. underwater sites are most frequently anchors, cannons, cannon balls, nails, razors, knives and tes of iron, while contact with sand and phosp- • Passivation - the metal forms solid corro- hates has a stabilising effect, and the compo- COPPER AND ITS ALLOYS sion products that adhere to its surface various other tools. unds created are relatively non-aggressive and prevent or restrict further attack. Me- towards the metal itself. Water rich in magnesi- Copper is a metal of characteristic light reddish tals sometimes corrode in environments Of all the metals in extensive use, iron is the most susceptible to corrosive processes. The um and calcium acts to strengthen the corrosion colour. It is relatively soft, very malleable and an where it would be supposed that passive layer, while a relatively high chloride content in excellent conductor of heat and electricity. It oc- films would develop to prevent attack. corrosion of iron is caused by oxygen and mois- ture. Initially, three oxides occur successively in seawater causes a strong corrosive attack which curs naturally as an ore, most frequently a sul- This may be due to the presence of certain ag- is only increased when the object is extracted. phide ore (chalcopyrite, covellite, chalcozine, iron in contact with air and oxygen: FeO, Fe3O4 gressive ions, chlorides being a prime example. The characteristics of an advanced stage of cor- bornite…), oxide ore (cuprite, tenorite…) and and Fe2O3. With the introduction of moisture Unlike other ions, chloride ions migrate through rosion are a blistered surface, cracked crust and carbonate ore (malachite, azurite…). Because of Fe2O3 converts to FeO(OH), which is, unlike the protective films and cause the metal beneath to a bulging accumulation of products on the surfa- its very high tendency to corrode and difficult corrode (CRONYN 1990,168-171). first three, amorphous in structure and no longer protects the metal from further corrosion. The ce of the object (BUDIJA 2002, 83-84; HAMIL- casting it is most often alloyed, above all with tin The process of corrosion in an underwater envi- chlorine and sulphur dioxide compounds present TON 1999, File 9). and zinc. ronment may be manifested as: further intensify this process, and various aero- • An alloy of copper and zinc is known as • Uniform corrosion - corrosion resulting bic and anaerobic bacteria certainly play a role The common products of corrosion on archaeo- brass. If the amount of zinc does not from an electrochemical reaction that oc- (KLARIû 1998, 69-70). logical objects made of iron alloys: exceed 20% the brass is yellow in colour, curs on the entire metal surface at almost IRON(II) HYDROXIDE - Fe(OH)2 while further increasing the proportion of the same rate. The activity of moisture also leads to the separa- LIMONITE – IRON OXIDE-HYDROXIDE - FeO zinc renders the brass whiter. • Galvanic corrosion - occurs when two tion of metallic salts, which act as an electrolyte, (OH) • An alloy of copper and tin is known as different metals or alloys are in electrical and an electrolytic reaction is created with ano- IRON(II) CHLORIDE - FeCl2 bronze and is of reddish-brown colour. contact through the action of an dic and cathodic areas. HYDRATED IRON(II) CHLORIDE - FeCl2*H2O Bronzes with over 20% tin are white in electrolyte (corrosive substance). The IRON(III) CHLORIDE – FeCl3 colour, and were used in the Roman peri- less noble metal in this pair corrodes Iron oxidises at the anode creating ferrous chlo- HYDRATED IRON(III) CHLORIDE – FeCl3*H2O od for the manufacture of mirrors. Bronze significantly faster than it would if it alone ride, while hydrogen is reduced at the cathode. FERROUS SULPHIDE - FeS with about 30% tin is known as speculum where present in the same electrolyte. Hydrogen, which is weakly conductive, gathers MAGNETITE – Fe3O4 metal, which is very hard, fragile and brit- • Fouling corrosion - corrosion caused by at the cathode and prevents further corrosion. In HYDRATED MAGNETITE – Fe3O4*H2O tle (BUDIJA 2001, 137). marine organisms, occurs when marine the presence of oxygen, however, hydrogen HAEMATITE – IRON(III) OXIDE – Fe2O3 The most frequent bronze finds at underwater organisms, such as limpets and molluscs, combines with oxygen as water or hydrogen HYDRATED HAEMATITE – Fe2O3*H2O sites are cannons, nails, weapons, various parts grasp on to a metal surface, develop, and peroxide eliminating the protective layer and the of ship's equipment and - depending on the sun- then separate small pieces of metal from electrolytic reaction continues until the entire It should be noted that iron chlorides are always ken ship's cargo - wether bells, vessels, small the surface. This process causes pits to surface is covered in the products of corrosion, a component part of the corrosive products of boxes, medallions, coins, needles, fibulae, vario- form on the metal under the marine orga- which then allows for the unimpeded activity of iron and that metal objects from underwater en- us tools and jewellery.

Conservation of Underwater Archaeological Finds - MANUAL 50 Joziü A.: The Conservation and Restoration of Metal Finds 51

When bronze corrodes there is an initial layer of of the object (BUDIJA 2001, 138-139; KLARIû most significant to silver corrosion are hydrogen vanced stage of corrosion typified by hard sca- red copper(I) oxide (cuprous oxide) that forms 1998,63-64; MAZZEO 2005, 29-43). sulphide and sulphur dioxide. In aerobic conditi- les and a disfigured, fissured surface. These on its surface mixed with tin oxide. Cuprous ons the oxidation of silver always involves scales are the result of the chloride and bromide oxide then hardens in the form of the mineral The basic patinas present on archaeological oxygen, but is assisted by hydrogen sulphide, frequent in salty environments. Chlorides react cuprite, which is reddish - brown in colour. This objects made of copper alloys are: which bonds the created Ag+ ion to highly inso- with the silver creating a layer of "horn silver," COPPER(I) OXIDE, Cu2O, CUPRITE – a red- layer is porous and the action of CO2 bonds an luble silver sulphide. while brown scales form in the presence of dish-brown compound; it always lies directly on external layer of basic carbonates to it. The 2Ag + H2S+ 1/2O2 ĺ Ag2S + H2O excess bromide. layer of copper carbonate is green - blue in colo- the metal. In the process the contact of silver with oxygen COPPER CORROSION SURFACE – copper ur, and its bases are the minerals green malac- COPPER(II) OXIDE, CuO, TENORITE – a black also creates a layer of the also black silver oxide corrosion may completely cover the surface of a hite and blue azurite. These minerals create a copper oxide; a transitional form to more stable parallel to the layer of silver sulphide. In silver-copper alloy, giving it the appearance of noble patina, uniformly distributed, showing all forms of patina. seawater a layer of silver bromide is also corroded copper. In the less advanced phase the detail and protecting bronze from further cor- MALACHITE, Cu2(OH)CO2 – one of the green frequent. The cited sulphide and oxide compo- points of copper corrosion can be seen on the rosion. Changes occur in the presence of chlori- basic copper carbonates. unds provide silver with a degree of protection surface of the object (KLARIû 1998, 107). ne which converts basic carbonate (malachite) AZURITE, Cu3(OH)2(CO3)2 – a blue copper car- from further corrosion, and provide an into nantokite. It acts upon metal making its sur- bonate; appears together with malachite. aesthetically pleasing patina the preservation of GOLD AND ITS ALLOYS face powdery and mottled green. Nantokite is CHALCONATRONITE, Na2Cu(CO3)2×3H2O – a which is always desirable. Changes occur in the hydrolysed to create hydrochloric acid, which blue-green sodium copper carbonate. presence of chlorine. Silver objects suffer most Gold is a soft and ductile metal of lustrous further reacts with the uncorroded copper. A ATACAMITE and PARATACAMITE, Cu2(OH)3Cl from reactions with the chlorine contained in the yellow colour. It is a very rare element. In nature further reaction in the presence of moisture and – of the same composition, but of different ground and in seawater. This creates silver chlo- we find it almost exclusively in its metal form, oxygen creates a pale green powdery patina of crystal structure; a basic copper chloride of light ride or "horn silver" that, unlike sulphides and while a small quantity of gold is found basic cuprous chloride (paratacamite). This kind green colour; soft, often powdery structure; oc- oxides, does not have the characteristic of pro- accompanying copper and silver ores. Gold is of corrosion is often referred to as bronze disea- curs on objects from soils rich in salts and on tecting the metal, and the process of corrosion the most noble of metals and is as such se, bronze cancer, bronze plague and malignant objects extracted from marine environments. lasts until all the silver is converted to a chloride exceptionally resistant to corrosion. It is overly patina. Malignant patina is recognisable by the BOTALLACKITE, Cu(OH)3Cl×H2O – of blue- making this corrosion destructive. When silver soft in its pure state and is most often alloyed bumpy protrusions it creates by the blistering of green colour; related to paratacamite. alloyed with copper (or some other metal) is cor- with silver, copper, or some other metal the patina under the influence of chlorine. The NANTOKITE, CuCl – forms a whitish waxy layer roded, the entire process is more complex as (FILIPOVIû, LIPANOVIû 1995, 1085-1089). The process usually affects smaller or larger areas of on bronze. We find it only accompanied by para- the appropriate copper compounds are formed archaeological finds made of gold most the object, and the focal area of the process is tacamite. One of the causative agents of cyclic parallel to the silver compounds. In these cases frequently found at underwater sites are various raised in relief and similar in appearance to corrosion, known as bronze plague (BUDIJA the less noble metal is always decomposed first kinds of jewellery. layered scabs. With time the affected area spre- 2001, 139-141). and these objects have a patina that is more ads through the depth and breadth of the object. characteristic of copper than of silver (BUDIJA The noble nature of pure gold lies is its preventi- For the most part metal objects extracted from SILVER AND ITS ALLOYS 2001, 5; HAMILTON 1999, File 13). on of natural corrosion - it is absolutely stable in the sea have active chlorides present and air and does not bond with oxygen at any tem- thereby bronze disease, which may result in pit- As an elementary substance silver is a lustrous perature. Pure gold does not corrode. Gold ting corrosion and the complete decomposition white noble metal, unusually malleable and duc- alloys that contain over 20% of other, as a rule tile. It has lower electric resistance and greater less noble metals, are subject to corrosion - heat conductivity than any other metal. There particularly sensitive to corrosion are gilded ob- are relatively small amounts of silver in nature. It jects where only a very thin surface layer is gol- is found for the most part accompanying lead Figure 4. Silver coins, Sveti Pavao site near Mljet (Photo: Figure 5. The gilded box and copper ores or as argentite Ag2S. Because M. Pešiü) of a sundial, Mijoka site at of its softness it is rarely used in its pure state Murter (Photo: A. Joziü) for the manufacture of works of art, and it is The visual characteristics of the corrosion of normally alloyed, most often with copper, tin or silver objects: gold (FILIPOVIû, LIPANOVIû 1995, 1079- BLACK LUSTROUS PATINA – this patina oc- 1085). The most frequent archaeological curs on objects of pure silver that have been underwater finds made of silver are coins and exposed to extended atmospheric action in a dry various kinds of jewellery. and saltless environment. Figure 6. The gilded PALE GREY PATINA – characteristic of a thin Sulphur compounds are the leading cause of box of a sundial, Mijoka layer of silver chloride on the object. site at Murter (Photo: A. Figure 3. A bronze bowl, Veruda site (Photo: A. Joziü) silver corrosion. Of the sulphur compounds the BLACK-GREY or BROWN SCALES – the ad- Joziü)

Conservation of Underwater Archaeological Finds - MANUAL 52 Joziü A.: The Conservation and Restoration of Metal Finds 53

den. Gold, as the most noble metal, is always phate forms on the surface of the lead protecting black stains. At these areas the metal is conver- toration procedures, in order to avoid unknowns cathodic in relation to other metals in a corrosive it from further corrosion. Mechanical damage of ted to a powdery grey dust, the object is rende- in some future procedure, i.e. so that the level of medium - they dissolve and the corroding alloy this layer can lead to a stronger corrosive attack red frangible and breaks easily - this process interventions conducted, the dimensions and becomes increasingly porous and brittle, and and the conversion of the object to basic lead lasts until the object is entirely decomposed. In scope, can be precisely determined. The thereby increasingly subject to corrosive proces- carbonate. seawater it has been demonstrated that the pre- preliminary phase, consequently, involves taking ses. Objects made of these kinds of alloys sence of sodium chloride promotes and accele- measurements of the object, photographing it, acquire the patina of the metal that has been The most frequent corrosion products on archa- rates the corrosion of tin (HAMILTON 1999, File makes sketches and documenting the state in added to gold (KLARIû 1998, 115; BUDIJA eological objects made of lead are various 14). which it was found. 2003, 78-82). oxides (PbO, PbO2), basic carbonates (2PbCO3 x Pb(OH)2), chlorides (PbCl2), sulphides (PbS) 2. DESALINATION OF THE OBJECT The visual characteristics of archaeological gold: and sulphates (PbSO4). Corrosion products on CONSERVATION - RESTORATION UNCORRODED – pure gold is relatively easy to lead objects extracted from marine environ- INTERVENTION ON UNDERWATER After initial documentation the objects are isola- visually identify. ments are stable. They may visually disfigure METAL ARCHAEOLOGICAL FINDS ted in polypropylene nets and placed in desali- COPPER CORROSION – visible on the surface the object, but they do not participate in chemi- nation baths. Desalination involves submerging

of objects made of an alloy of gold and copper. cal reactions leading to the further corrosion of the objects in vats filled with tap water with the Conservation - restoration work on underwater SILVER CORROSION – visible on the surface lead. These objects require cleaning exclusively addition of the appropriate inhibitor, and regular archaeological metal finds can be divided into of objects made of an alloy of gold and silver. for aesthetic reasons and to reveal surface deta- renewal with fresh solution. The addition of the phases: SCRATCHED SURFACE – gold is an extremely il (FILIPOVIû, LIPANOVIû 1995, 849-855; HA- inhibitor is an appropriate cautionary measure to 1. Photographic documentation and a de- soft metal and small scratches are easily visible MILTON 1999, File 14). prevent the continuation of corrosion processes, tailed description of the initial condition on archaeological object or their acceleration, which, as a rule, is the ca- 2. Desalination of the object TIN AND ITS ALLOYS se when metal objects are extracted from a ma- 3. Preliminary investigation rine environment. The most frequently used are 4. Cleaning the object As an elementary substance tin is a silver - alkaline inhibitors such as sodium carbonate, 5. Active stabilisation white metal, not overly hard and very malleable. sodium sesquicarbonate and sodium hydroxide. 6. Gluing broken objects and possible recon- At normal temperatures it undergoes practically The amount of inhibitor added must be such that struction Figure 7. Lead anchor stock, ýiovo site (Photo: A. Joziü) no change either in air or water. One of the key it maintains the pH of the solution above 8 7. Applying protective coatings uses of tin is to create alloys, bronze above all. (HAMILTON 1999, File 9). The water in the 8. Drafting technical documentation on inter- LEAD AND ITS ALLOYS Objects of pure tin are very rare finds at baths is changed, as a rule, every four weeks, ventions conducted underwater archaeological sites. While it is i.e. when the concentration of secreted salts

Pure lead is a heavy, silver-blue, lustrous metal. relatively resistant to corrosion, it is sensitive to reaches a constant maximum. The concentrati- The cited phases of conservation - restoration It is very soft, very dense and has a low melting changes in temperature that cause changes in on of salt is monitored via electrical conductivity, intervention can be applied with equal effective- point. In relation to other metals it is a relatively the structure of the metal. which grows proportionally with the increasing ness on archaeological metal objects found in poor conductor of electricity and heat. Lead and quantity of salt in the solution. The water is underwater environments and at those found in its compounds are very toxic. It occurs most Initially this is visible as a loss of surface lustre changed successively, with the maximum con- other environments, the only difference being frequently as a sulphide, PbS, the mineral gale- and later as the formation of expanding grey- centration dropping with every new change. It is that the lack of marine incrustations and the na. Frequent lead finds at underwater sites and important to proceed gradually to avoid the lower chloride content significantly reduces the shipwrecks are weights, cannon balls, various overly speedy release of salts, which could cau- time required to process and stabilise these ob- ship's repair patches, cartridges for weapons se further damage to the object. In the last few jects. and anchor stocks. changes tap water is replaced with distilled

water, which accelerates the desalination effect. 1. PHOTOGRAPHIC DOCUMENTATION AND Lead is a quite stable metal that turns grey in When desalination is completed objects are ta- A DETAILED DESCRIPTION OF THE INITIAL contact with air relatively quickly by the formati- ken out of the water and left to air dry, taking CONDITION on of an oxide - carbonate layer that protects the care to avoid significant oscillations in air tempe-

lead from further reaction with the environment. rature during the drying procedure. Metal objects, like all artefacts must be recorded In natural waters, in which oxygen is present, before they receive any treatment. The ethics of lead undergoes corrosive dissolution as the re- 3. PRELIMINARY INVESTIGATION conservation - restoration intervention dictates sult of electrochemical processes. But, because the documenting of the relationships between of the common occurrence of hydrogen carbo- The selection of materials, tools and the met- the original state of the object and all changes nate and sulphate in natural waters, a highly hods of treating an object should, along with an Figure 8. A tin box, Mijoka site at Murter (Photo: A. Joziü) that are the consequence of conservation - res- insoluble layer of basic lead carbonate and sul- understanding of the characteristics of the metal

Conservation of Underwater Archaeological Finds - MANUAL 54 Joziü A.: The Conservation and Restoration of Metal Finds 55

of which an object is made, be preceded by an 4. CLEANING METAL OBJECTS Small hand - held tools include: various chisels, rosion. These provide high cleaning power but analysis of the damage and the state of an ob- pins, scalpels and brushes. To avoid marking minimal stress and vibration to the object. Mec- ject. The examination of excavated material is The cleaning of metallic archaeological finds is a the artefact, the tool should be softer than the hanical cleaning should be done carefully, with fundamental to archaeological conservation. non - reversible stage in the conservation and material being cleaned but care should be taken full concentration and great caution and always The conservator looks at any remaining original restoration process. What is removed cannot be to avoid using tools that, when abraded, could using a magnifying glass or microscope. Care- material together with its deterioration products recovered. In the entire process this is the most adhere to the material. Ultrasonic vibrations can lessness can very easily destroy details and ca- and any adhering associated material. In order sensitive phase, as the thickness of calcareous, be used either transmitted from small mobile use the object to lose its authenticity. to understand what s/he is looking at, a conser- oxide and corrosive accumulation above the heads as in dental descaling units or in tanks vator must have a good knowledge not only of surface that is to be removed has to be well jud- into which objects are immersed in a liquid. A Chemical cleaning materials and how they decay, but also of histo- ged. Various corrosion products form over the dental micromotor is the most commonly used The chemical cleaning of archaeological metal rical technologies. Objects should be examined centuries on archaeological metal objects and power tool; it can be fitted with a variety of grin- objects is nowadays for the most part avoided. It to establish the number of layers, chemical com- their surface is, as a rule, preserved in a minera- ding wheels and burs of various shapes and is used sometimes to clean objects made of lea- position, state of the surface, the possible pre- lised form. This is referred to as the original sur- sizes. The use of micro sandblasting devices is d, silver or gold that are, as a result of their sof- sence of decorations, inserts of other metals, face. The original surface is one of the corrosion widespread and it is the most useful tool tness, easily damaged by mechanical cleaning. the remains of gilding, silver plating and other layers that delineate the original shape of the powered by compressed air.The actual micro The most frequent chemical cleaning agents are parameters. This information is then used not object and may be only a few millimetres thick, sandblasting procedure is very simple. The ob- mildly acidic or alkaline and neutral water-based only to determine the mode of treatment for the but is of exceptional importance to the restorer ject is held by hand in the micro sandblasting solutions, while other solvents are rarely used. artefact but also to reveal how it was originally and archaeologist as it contains information abo- chamber. The other hand is used to control the The most important attribute of these agents is made, what it was used for, and even the signifi- ut the object from the time when it was in use. nozzle from which sand is ejected under pressu- that they eliminate corrosion accumulations but cance of the context in which it was found This layer must, therefore, be preserved and re. The air and sand pressure is set using a re- do not erode the metal we are cleaning. Their (CRONYN 1990, 58). only the corrosion products and accumulations gulator and should be reduced when approac- key drawback is that they, as a rule, also remo- above it are to be cleaned (DORAýIû 2000, hing the original surface. When applying micro ve the original layer of patina and that objects Preliminary examination includes a visual in- 133). sandblasting one should bear in mind the proper thus treated lose their original brilliance. In ge- spection of the object and an inspection under choice and granulation of the abrasive substan- neral, however, chemical cleaning is difficult to magnification (5X, 10X, 20X, 40X). Based on the Mechanical cleaning ce. The selection of the appropriate type control, as the agents often penetrate micro- acquired information we can decide on possible The mechanical method is recommended and (corundum, glass beads, walnut shells…) and cracks to reach the weakened artefact. It is vital laboratory or chemical analysis of the metal ar- used to remove corrosion products and to clean size (50-110 ȝm) of abrasive depends on the that objects are thoroughly rinsed with water chaeological object and radiographic filming. an archaeological metal object to its original sur- kind of metal and the level of corrosion on the after chemical cleaning to eliminate any soluble face. Wherever possible, the cleaning of metallic object. During sandblasting the abrasive strikes product and any remains of the chemicals used To establish the state of the interior of a metal archaeological objects is carried out the surface of the object, entering the smallest so that they do not contribute to further corrosi- object it is best to make use of x - rays. X - rays mechanically as these methods are the most pores and slowly removing the accumulated cor- on. pass through metal oxides more readily than controllable when done by skilled hands. through the metal itself, and an x - ray gives a Cleaning by electrolytic reduction much better picture of the extent of oxidation Mechanical cleaning is the basic form of work on Electrolytic cleaning involves a current flow that than any other method. On an x - ray we can metal archaeological objects and is done using is almost the reverse of what occurs during elec- observe the thickness of the layer of corrosion, a wide range of small hand-held tools and tools trochemical corrosion. Electrolytic reduction is a the presence of other metals and materials and powered by electricity, compressed air, or ultra- method involving the flow of electric energy opt for the most appropriate conservation met- sonics. between two metals submerged in and hod. X - rays provide us with a two - dimensional electrolyte developing hydrogen, which then image of the object. A step beyond imaging ar- acts as a reductive substance. In electrolytic chaeological objects using x - rays is the use of reduction electricity is introduced from an CT. This is a modern method that produces a external source such as a battery or transformer three-dimensional image providing us with in- rectifier. sight deep into the object. We can calculate the thickness of the metal core, the oxide crust or of Corroded metal objects serve as the cathode a non-metal lying on the original object. These (negative electrode) while the anode (positive kinds of images tell us much more about an ob- electrode) is made of stainless steel. The most ject hidden under calcareous, oxide and corrosi- frequently used electrolyte is a water solution of ve accumulations (DONELLI, MIHANOVIû 199- Figure 9. A micro sandblasting device and chamber Figure 10. Mechanical cleaning an iron object under a sodium hydroxide. The intensity of the reduction 7/1998, 459-477). (Photo: A. Joziü) microscope (Photo: M. Mustaþek) is proportional to the strength of the electricity.

Conservation of Underwater Archaeological Finds - MANUAL 56 Joziü A.: The Conservation and Restoration of Metal Finds 57

When the current is turned on, the inert metal Archaeological metal objects usually lack a me- the cation Cu+, benzotriazole blocks the formati- becomes the anode whilst that to be cleaned is tal core and are preserved for the most part in a on of nantokite, a basic copper chloride, and the cathode being fed with electrons. The main mineralised form and where electrolytic reducti- thereby the further cyclical corrosion reaction reduction reaction at the cathode is the formati- on is used in preference to mechanical methods (HAMILTON 1999, File 12; BUDIJA 2001, 147). on of hydrogen gas which – forming as bubbles because it is "cheaper," being less labour inten- Benzotriazole has been demonstrated as a very on the metal surface below the corrosion crust – sive, the cost to the artefact itself must be taken effective copper and copper alloy corrosion inhi- tends to force this layer off into the bath, thereby into account (CRONYN 1990, 174). bitor. Research has, however, shown the com- "mechanically" cleaning the metal. pound to be toxic - new effective, but 5. ACTIVE STABILISATION ecologically acceptable corrosion inhibitors sho- uld be found. After the removal of a metal object from an envi- Figure 13. An iron object isolated in a polypropylene net ronment in which the metal and the corrosion after the sulphite procedure (Photo: A. Joziü) 6. GLUING BROKEN OBJECTS AND products have been in equilibrium for centuries, POSSIBLE RECOSTRUCTION attempts must be made to stabilise it. The active is changed once a month for as long as chloride stabilisation of archaeological objects implies presence can be demonstrated. Once the desa- Damaged metal objects, meaning above all bro- procedures that involve direct intervention on lination is completed the treated objects are rin- ken and cracked objects received in two or more the object to stop decomposition processes. sed in copious quantities of distilled water. fragments, are simply glued together. The re- This includes, for example, eliminating chloride commended method is to first undertake a ions, using corrosion inhibitors, synthetic impre- The active stabilisation of bronze objects is preliminary bonding of the fragments with rever- gnation materials and the like. In contrast to acti- usually achieved by submerging them in a 3% sible cyanoacrylate glue, and then to strengthen ve stabilisation, passive stabilisation does not alcohol solution of benzotriazole. When bubbles the binding with two - component, also reversib- Figure 11. Schematic depiction of the electric circuit of intervene directly on the metal object, but in the stop evolving, after about 24 - 48 hours, the ob- le, glue, in the process of which we may also electrolytic cleaning (Drawing: A. Joziü) environment around it (microclimate control, use jects are extracted from the solution and allowed apply reinforcement in the form of glass fibres. of dehumidifiers etc.). to dry. Upon drying the excess benzotriazole is The damaged surface of metal objects may, if Secondary reduction reactions of the corrosion removed with a pad soaked in acetone. Benzot- required with the aim of achieving structural crust form either more easily removed corrosion The role of chlorides is significant in the corrosi- riazole is a vapour phase corrosion inhibitor that stability, be filled with the same two - component products or powdery metal, which is then brus- on of metal objects and we can say that the pro- effectively inhibits the anodic reaction of copper glue with the addition of the appropriate pig- hed off. Hydrogen forms on the cathode, which blem of their removal is one of the key problems dissolution in an acid medium, and stabilises an ment. Missing pieces are most readily fabricated reduces and decomposes the corrosion layers in the conservation of metal archaeological ob- oxide film in an alkaline medium and thereby from a plastic mass. The most frequently used of salt while the chlorides from the cathode mig- jects. The most successful method of eliminating increases its corrosion protection. By bonding to are two - component epoxy resins to which the rate to the steel anode. The strength of the chloride ions from iron objects is the standard electricity and the duration of this procedure procedure in a solution of sodium sulphite. The must be controlled by monitoring the corrosion procedure itself involves isolating the objects in potential (voltmeter, referent electrode), as it polypropylene nets and placing them in a sulphi- would otherwise completely remove all corrosion te procedure vat. The vat is then filled with a layers from the metal object exposing the strip- solution of sodium sulphite (6.3%) and sodium ped metal core, which is not our goal. hydroxide (2%) in distilled water. The conditions of the procedure are anaerobic (the vessel is hermetically sealed) to prevent the oxidation of sulphite into sulphate, which would destroy the material. The cited solution circulates in the vat at a temperature of 50ºC and extracts the chlori- de ions responsible for deterioration from the object. A high pH level and elevated temperatu- re encourage the speedy and effective migration of chloride ions from the object in the solution (HAMILTON 1999, File 10B).

Figure 14a. Figure 14b. Figure 14c. The concentration of chloride is determined by Figure 12. Setting of a bronze cannon for electrolytic Figure 14a, 14b and 14c are showing the device that determines the concentration of chloride and a schematic depiction of reduction process (Photo: A. Jeliü) potentiometric titration. The solution in the bath the results (Photo: A. Jeliü)

Conservation of Underwater Archaeological Finds - MANUAL 58 Joziü A.: The Conservation and Restoration of Metal Finds 59

appropriate pigment is added and a possible Paraloid B72 and Cosmoloid H80 are the most Technical documentation must, above all, inclu- admixture of the appropriate powdered metal. frequently used protective coatings for archaeo- de photographs of the object prior to, during and This is a relatively easy procedure and, what is logical metal objects. Paraloid B72 lacquer is a after interventions undertaken, sketches of the most important; these kinds of supplements are long-lasting thermoplastic, acrylic resin that does object, reports on laboratory analysis that may completely reversible. We should only undertake not yellow and is resistant to alkalis, acids and have been conducted and radiographic images the reconstruction of metal objects if we have a mineral oils. It is prepared as a solution (2 or of the object. To reduce unknown variables in very good grasp of the processing of this materi- more percent) in the appropriate organic solvent any future procedure, i.e. to precisely determine al and if the original appearance of the object is (acetone, xylene, toluene). Cosmoloid H80 is a the level of interventions undertaken, proper evident from the fragments, and we should keep microcrystalline wax prepared as a solution with documentation should describe all interventions in mind that our actions must not alter the a percentage of toluene. Bronze, silver and undertaken on the object and all materials used. authenticity and condition of the object. possibly gold objects are protected with Paraloi- The importance of properly drafted technical d, while a mixture of Paraloid and Cosmoloid is documentation is unquestionable, and a step 7. APPLYING PROCECTIVE COATINGS used as a protective coating for iron and lead further should be to organise the documentation objects. in well-designed and broadly accessible databa- Protective coatings on metal objects may be ses. This would allow easy access to a great applied by coating, spraying and immersion. It should be noted that a protective layer on ar- quantity of valuable data and thereby to a better Applying a coating with a brush is an acceptable chaeological objects does not guarantee perma- assessment of individual methods of protection. method if the object in question has a smooth nent protection and that they need to be surface. Otherwise working with a brush does periodically renewed. Conserved and restored not allow us to cover and fill small pores and metal archaeological objects need to be handled CONCLUSION there is a great likelihood that air could be trap- with care and their state monitored, and a pro- ped in them, and with it the potential danger of fessional should be promptly notified of any Conservation - restoration intervention on archa- the blistering of the coating and the develop- changes. It is particularly important to avoid gre- eological metal objects is a very sensitive and ment of corrosion foci. When applying the coa- ater oscillations of temperature and relative demanding operation and should not be under- ting by brush the layer of coating must be as humidity and to continually monitor the microcli- taken without an understanding of treatment uniform and thin as possible, as this allows us to matic conditions in the space in which the ob- ethics. The success of the intervention depends apply several layers and achieve a durable mul- jects are kept. on a commitment to recognise the original surfa- ti-layered coating. By spraying a protective coa- ce under corrosion accumulations, to ensure ting on the surface of a metal we achieve a uni- 8. DRAFTING TEHNICAL DOCUMENTATION that the vital interventions undertaken are rever- form thickness and a relatively good filling of sible and that they do not, in the final tally, alter pores, but insufficiently good if working with a The original condition of the object and all chan- the character of the object. Technological and very porous or rough metal surface. The best ges that are the result of conservation- scientific progress brings with it new develop- results are achieved by applying the protective restoration interventions should always be docu- ment in all fields of activity, including in the fields coating by immersion. Besides the fact that the mented, and drafting technical documentation of conservation and restoration. Every restorer coating fills every pore, this method also has the should always follow the completion of conser- should, therefore, keep abreast of current deve- effect of reinforcing the object, especially an ob- vation - restoration work on metal archaeological lopments, accept new methods, new ject of porous structure. finds. experiences, perfect their craft, exchange infor- mation and do everything they can to provide the best possible research of objects from ar- chaeological sites and their high quality and pro- fessional conservation and restoration.

Figure 15. Documenting the gradual removal of corrosion and calcareous accumulations from the head of the ancient Apoxyomenos statue – a valuable underwater bronze find (HRZ photo archives)

Conservation of Underwater Archaeological Finds - MANUAL 60 Jeliü A.: Organic Material 61 VII. Organic Material the total mass of wood. Cellulose molecules join wood, depending on the ambient humidity, can to form microfibres, and they in turn form fibres range from 25 to 65%, where about a third is that give a wood cell its strength and durability. made up of hygroscopic or bound moisture Anita Jeliü organic materials, which encompasses all other Within the structure of wood, cellulose is surro- (MALINAR 2007, 86). artefacts made of plant fibres, animal tissues or [email protected] unded by hemicellulose and lignin. Hemicellulo- bone. se is the second most important carbohydrate ARCHEOLOGICAL WATERLOGGED WOOD present and accounts for 20 to 30% of wood's cell mass. The function of hemicellulose is not Wood extracted from water (rivers, lakes or sea- INTRODUCTION WOOD yet fully understood, but it is presumed that is s) and wood extracted from wetland is referred serves as a binding structure between cellulose to as archaeological waterlogged wood. It can Organic material is a category of materials that Archaeological wood refers to all finds of and lignin. Lignin, which accounts for 20 to 30% be defined as wood that does not contain or include all artefacts made of plant fibres, animal wooden artefacts and other old wooden manu- of wood's cell mass, serves as the "glue" that contains little air within its cells, capillaries and tissues or bones. The most frequent underwater factured goods that reveal information about holds the microfibres together, and gives wood micro capillaries. Its structure is also weakened archaeological material of organic origin found in people and culture. Because of its mechanical its strength. It is also the most stable chemical by biological decomposition (RODGERS 2004, rivers, lakes, the sea or wetlands are wood, bo- properties, workability and relatively easy compound in the structure of wood (Figure 1) 39). ne, ivory, leather, textile and cord. The level of accessibility, wood has from time immemorial (JONES 2003, 53, 54; FORS 2008 13, 14). preservation of archaeological objects of organic been used in the most diverse applications cha- Archaeological waterlogged wood often looks materials that have been underwater or in wet racteristic of the period from which they origina- The basic element in the structure of wood is the well preserved; an appearance contributed to by soil for years differs, and depends on the type of te. But while it has been very extensively used, cell that, in its living state, consists of a membra- inorganic, cold and dark underwater conditions material, the conditions of the environment in its susceptibility of decomposition under the in- ne and protoplasm. When cells die, the protop- that slow biological decomposition. Waterlogged which they were found, and above all of their fluence of atmospheric conditions, microorgani- lasm gradually disappears. What remains is only wood is, however, very weak and deteriorated biodegradation by various microorganisms. The sms and other destructive factors has seen only the membrane - i.e. the walls, which have thic- because water soluble substances such as conservation of artefacts of organic materials, a small percentage wood preserved (MALINAR kened and lignified - and the lumen (the cell starch and sugar, mineral salts, pigments and from their extraction from water or wet soil to 2007, 85). cavity) filled with air or water, depending on the tannins are the first to be dissolved in storage and display, is a long process that de- level of moisture in the wood. The cell walls, underwater conditions. Cellulose passes through mands competence, patience, commitment and Wood, as a substance produced by plants, is which are hygroscopic, absorb or transpire mois- the process of hydrolysis and attacks by anaero- dedication to the undertaking. The organic mate- chemically composed of: carbohydrates ture, depending on the ambient humidity. This is bic bacteria that decompose it leaving only the rials found are most often from a shipwreck and (cellulose, hemicellulose), lignin (phenolic subs- the process of water absorption and desorption, lignin network. Over an extended period of time we find small ship's gear, ship parts and partial tances) and other components (aliphatic acids, which results in changes to the dimensions and the lignin will also decompose. The result of cel- or entire sections of a ship's structure. alcohols, proteins and inorganic substances) in volume of wood. The moisture level of raw lulose and lignin decomposition is an increase in a significantly smaller amount. Cellulose is the the space between cells and the molecules In this chapter organic material has been divide most important of these molecules and accounts within cells, rendering the wood more porous into wood, as a category unto itself, and other for the majority of the cell, about 40 to 50% of and more permeable to water. All of the cavities are filled with water, and it is this absorbed water and the remnants of the lignin that maintain the

original form of the wood. This, seemingly well preserved wood is soft and spongy to the touch and will only retain its original form while it is wet. Abruptly exposing wet wood to air will cau- se excess water to evaporate, in the process of which the force of water surface tension causes already weakened cell walls to rupture. Signifi- cant changes in dimensions take place, i.e. the contraction, delamination and deformation of the wood. The changes in dimension depend on the level of decomposition and the amount of water present. As the wood dries the changes in di- mension are greatest in the direction of the Figure 2. Graphic illustration of raw wood shrinkage wood's annual growth rings (tangential shrinka- (JONES 2003, 64) Figure 1. The structure of wood (JONES 2003, 54) ge), somewhat less in the direction of the

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medullary rays (radial shrinkage), and in insigni- intervention and that it does not alter the charac- documentation of the state of the object as it ficant amounts parallel to the grain of the wood ter of the object (FORS 2008, 6, 7). was found. This phase involves photographic (longitudinal shrinkage) (Figure 2). Dimensional documentation prior to the start of conservation- changes which are due to moisture loss or The basic conditions that must be secured for restoration interventions, a scale drawing is ma- dehydration are present even at freshly cut the process of conserving waterlogged wood are de or at least a sketch with indications of the wood but in smaller percentage, for instance the area in which the process is to be conducted basic dimensions (Figure 3). Written documenta- freshly cut oak can shrink 4% radially and 8% and the financial means for both the process of tion is also drafted with a detailed description of tangentially when air dried, while waterlogged conservation itself and for the fabrication of a the object's appearance. oak can shrink over three times more. It is valid pool and the procurement of the impregnation in general that dimensional changes depend on substance. It is also important that space be 2. Cleaning the object the degree of degradation and amount of water provided for the exhibition of the object after the Wooden artefacts extracted from wet soil, present, in fact more water present means less conservation process has been completed - a muddy riverbeds or the seafloor may be covered cellulose and lignin and that is also the normal requisite disregarded in most cases. Given that by accumulations of impurities and sediments. result of the biological and chemical decomposi- the process of waterlogged wood conservation These accumulations are removed slowly under tion of the wood. Changes in the wood resulting demands a significant amount of time, we re- a slow stream of water (Figure 4). Use soft brus- from dehydration are permanent because commend initiating the process only after the hes and increase the temperature of the water subsequent hydration of the wood will not return necessary conditions have been provided for to 30ºC to remove tougher incrustations. The the cell to its original state. Leaving the wood at (MALINAR 2007, 93). calcareous shells of marine organisms are a the find site is, therefore, recommended until the frequent component of accumulations on the required conditions for its conservation have Conservation - restoration work on archaeologi- surface of wooden objects extracted from a ma- been secured, with the necessary protection of cal waterlogged wood can be divided into the rine environment - they are removed the site from possible devastation. If the wood following phases: mechanically using scalpels of various profiles Figure 4. Cleaning under a slow stream of wather with has already been extracted from the water it 1. Photographic documentation and a detai- and sizes. Traces of iron elements may also be brushes (Photo: M. Mustaþek) should be submerged in a pool or some other led description of the initial condition present on wooden objects - visible as rusty between solids and water contained in the wood water-filled vessel to prevent the process of 2. Cleaning the object orange to reddish-brown accumulations on their is an important piece of information in the con- dehydration until the conditions required for its 3. Preliminary investigation surface. These kinds of accumulations are re- servation of archaeological waterlogged wood conservation have been secured (CRONYN 4. Desalination moved by treating the object with a 5% solution because, besides being an indicator of the level 1990, 248-254; SMITH 2003, 22, 23). 5. Impregnation of disodium salt of ethylenediaminetetraacetic of the wood's degradation, it also determines the 6. Drying acid (EDTA: C10H14O8N2Na2*2H20) in water. Cle- quantity of impregnation substance required in THE CONSERVATION OF WATERLOGGED 7. Drafting technical documentation aning is often carried out in parallel to desalinati- some conservation methods. Wood with higher WOOD on - which also has the effect of accelerating the moisture content, i.e. fewer solids, will, for latter process (JONES 2003, 35, 36). example, require a greater quantity of impregna- The conservation of archaeological wood allows tion substance than wood that contains less mo- for its further study and exhibition. An important 3. Preliminary investigation isture. The moisture content of wood is determi- aspect of the conservation of artefacts of Preliminary investigation always includes a visu- ned by the thermogravimetric procedure. A waterlogged wood is their stabilisation, i.e. al examination and in some cases taking sam- wood sample of several grams is first weighed in strengthening their structure and maintaining ples, determining the moisture content, the type its waterlogged state and is then dried in a dry their appearance and original dimensions. It is a and age of wood and x - ray imaging. Besides kiln up to a constant mass. After weighing the complex process that includes replacing water describing the appearance and shape of the dried sample the percentage of moisture contai- with an impregnating substance that will wood, a visual examination also describes its ned in the wet sample is calculated with the strengthen the structure of the wood and to un- texture, durability and hardness. following equation (MALINAR 2007, 93): dertake the removal of the water in a fashion that will not cause the wood to shrink or come Sampling precedes every analysis, and the size ȍ = [( A – B ) / A] x 100 ( % ) apart. There are a number of methods of con- and method of sampling depends on the Where: A = the mass of the wet sample servation known to us that differ one from the Figure 3. An example of taking measurements and produ- analysis. For most analyses sampling needs to B = the mass of the dry sample other by the impregnation substance used and cing a drawing (Photo by: A. Jeliü) be undertaken while the wood is in water, after the process whereby it is applied, and each of cleaning, prior to or during desalination, but The greater the percentage of moisture in the these methods should conform with the basic 1. Photographic documentation and a detai- certainly prior to the process of impregnation. sample of waterlogged wood, the smaller the principles of conservation such as the led description of the initial condition quantity of solids, i.e. cellulose, in the structure reversibility of the process, a minimum level of The conservation process begins with the initial The quantity of moisture, i.e. the relation of the wood, and a greater quantity of impregna-

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tion substance required. "non - porous" because they lack vessel pores. als, mostly metals, in the same room or environ- and water with the general formula HO- Typical examples of softwood are pine and spru- ment in which the treated wood is stored. Desali- (CH2OCH2)n-H, where "n" is the number of mo- The moisture content of wood can also be deter- ce. This classification is not really related to the nation is carried out by submerging the wood in nomers in the PEG molecule - PEG 200, for mined as the ratio of water to dry sample, where hardness of the wood because some softwoods a pool of clean tap water to which a disinfectant example, has four monomers in its chain, and the formula is: are harder than hardwoods, it is actually based has been added to prevent the development of n=4, while PEG 4000 has ninty monomers and on plant reproduction (JONES 2003, 51). harmful microorganisms. The disinfectant may n=90. It is used in the conservation of Umax = [( A – B ) / B] x 100 ( % ). be a fungicide, algicide, orthophenyl phenol, but waterlogged wood as a replacement for water in The age of wood is not essential data to the the most commonly used is a mixture of boric the structure of wood because it forms hydrogen The results are frequently over 100% but it is not conservation process. The age of a wooden ar- acid and borax because of its lesser toxicity. A bonds and provides mechanical support of dete- uncommon to find wood that contains more than tefact may be approximately determined from 2% solution of a mixture of boric acid and borax riorated wood. There are several kinds of 500% or even 1000% of water. Wood containing sources such as the dating of the site or in a ratio of 7:3 is added to the desalination polyethylene glycol that differ one from the other more than 200% of water is considered to be shipwreck. More precise data on the time the water. The water in the desalination pool is by molecular mass. Polyethylene glycols of degraded. According to the amount of water pre- wooden artefact was created is acquired using changed, as a rule, every four weeks, until the lower molecular mass, such as PEG 200 to PEG sent waterlogged wood is often classed as: technical methods such as the radiocarbon da- concentration of excreted salts reaches its con- 600, are liquid at room temperature, and penet- ting method, i.e. dating by way of the radioactive stant maximum. With successive changes of the rate the structure of wood deeper, while - Class I: Wood containing over 400% of water. isotope of carbon, 14C. This method can determi- water, i.e. with every new change of water, the polyethylene glycols of greater molecular mass, This material is very soft and almost no hard ne the age of other organic substances such as concentration maximum drops. This process is such as PEG 1500 through to PEG 4000, are in core is present. the age of textile or bone. The age of wooden monitored by determining the quantity of a solid state, and while they penetrate less they - Class II: Wood containing 185 - 400% of water. objects can also be determined by the dendroc- excreted salts, i.e. chloride, in a sample of the are superior in terms of stabilizing the structure A hard core is present, but relatively small. hronological method, which establishes age by water used for desalination. The electrical of wood. They are soluble in water, alcohol, ben- - Class III: Wood containing less than 185% of measuring the growth rings of wood and their conductivity of the water sample is measured zene and other organic solvents and, because water. A hard, little deteriorated core is present pattern. with a conductivity meter - it grows proportionally of their low toxicity, are numbered among subs- below a thin decayed surface layer. This class of with the increase of salts in the solution. More tances that do not present a health risk wood is the most difficult to conserve (JONES X - ray imaging is used to establish the presen- precise values are arrived at by measuring the (HAMILTON 1999, File 6; JURIû 1995, 79; 2003, 57; DE JONG et al 1979, 23). ce of metal within wooden artefacts, or on their concentration of chloride in the sample by po- http://www.maryrose.org/) surface if we speculate that metal may be pre- tentiometric titration (Figure 14; page 57). When sent under calcareous deposit layers. X - rays the measured value falls to the value for clean Conservation of waterlogged wood with penetrate wood with more intensity than metal tap water, the desalination process is deemed polyethylene glycol simultaneously eliminates and these images provide us with precise data completed. If possible, continuing desalination in water and impregnates wood. Wood, if on the presence of metal. Determining the age distilled water is recommended to reduce the necessary previously isolated in a polypropylene of wooden artefacts, the species of wood and x - quantity of chloride in the wood to a minimum net, is placed in a vat containing a PEG solution. ray imaging are analyses done in specialised (BORRELLI 1999, 3; MALINAR 2007, 93). laboratories. 5. Impregnation Markers for measuring changes in dimension The conservation of waterlogged wood is a Figure 5. Graphic illustration of hardwood and softwood, (radial and tangential shrinkage) can be placed complex process that involves impregnating magnified 250 times (Image from http:// at characteristic points on the wood in this pha- wood, i.e. replacing water with a material that toolboxes.flexiblelearning.net.au) se of the conservation procedure. The data from will strengthen the structure of the wood and to The species of a wood artefact is determined by measurements before and after impregnation undertake the removal of the water in a fashion ascertaining its macroscopic and microscopic will establish the percentage of the wood's shrin- that will not cause the wood to contract or come characteristics. There are two broad categories kage (MALINAR 2007, 93). apart. There are a number of methods of con- of wood, hardwoods and softwoods (Figure 5). servation known to us that differ one from the Hardwoods are more dense and classified as 4. Desalination other by the impregnation substance used and angiosperms, which refers to broadleaf trees or Besides water, wood extracted from the sea the process whereby it is applied. The most deciduous trees. They are considered "porous" contains salts, and desalination is essential. Salt common techniques for treating waterlogged because they have vessel pores. Typical is hygroscopic and would absorb water from the wood are discussed below. examples of hardwoods are oak and birch. air after the conservation process if not elimina- Softwoods are less dense and classified as ted. That would wet the impregnation substance Polyethylene glycol (PEG) method gymnosperms and they are needle - bearing and dissolve it at elevated relative humidity le- Polyethylene glycol (PEG) is a synthetic polymer Figure 6. Adding PEG in vat containing waterlogged trees or evergreen trees. They are considered vels. Also it may adversely affect other materi- constructed of the monomers ethylene oxide wood (Photo: A. Jeliü)

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Disinfectant is used if water is flammability (HAMILTON 1999, File 6). powder on the surface of the treated wood used as the solvent - for example (Figure 9). Preventing this synthesis and elimi- a 2% solution of a mixture of boric The method of conservation with polyethylene nating synthesised sulphuric acid and its salts is acid and borax in a 7:3 ratio. If glycol is one of the first and the most frequent a major problem affecting wooden finds conser- alcohol is used as the solvent di- methods used. However, laboratories that intend ved using the PEG method. sinfectant is not required. The tem- to conserve large artefacts of waterlogged wood perature of the solution in the vat, must be prepared to make major investments in thermally isolated and covered, is both equipment and chemicals. A substantial vat gradually increased until, after a must be constructed with the capability to heat few days or weeks, it reaches a and circulate the solution and there is also a temperature of 60°C. During that considerable amount of PEG required, while time the percentage of PEG is in- conserving small artefacts is a simpler process. creased as new and previously Small vats are needed that can be placed in a calculated quantities of PEG are thermostatically controlled oven and only a small added to the solution on a daily amount of PEG is required (HAMILTON 1999, Figure 7. An example of the graphic depiction of the relation between theo- basis (Figure 6). The size of the File 6). Regardless of investment it is still the retical PEG concentrations in a solution through a 28-week period and tho- PEG increments is dependent most suitable method for the conservation of se established by analysis (MALINAR 2007, 106) upon the condition, size and speci- large artefacts of waterlogged wood. The well- Figure 9. An example of the synthesis of sulphuric acid es of the wood being treated known 17th century warship Vasa (Figure 11; and its salts on the surface of wood conserved using the (HAMILTON 1999, File 6; MALINAR 2007, 94- PEG solution instead of water. It is recommen- page 11)and the 16th century warship Mary Ro- PEG method (Photo: A. Jeliü) 105). ded that the wood be dehydrated before being se where conserved using this method. Wooden placed in the PEG/alcohol solution. Dehydration ship's structures are conserved first by spraying Sucrose method Two techniques of adding PEG are used, and is done by placing the wood in at least three with water to effect the essential process of de- The method of conserving waterlogged wood we differentiate between the two - phase and baths of ethanol. However, it is not critical that salination, and then with a PEG solution in the with sucrose (sugar) was developed as an alter- parallel methods. In the two - phase method all the water must be removed from the wood impregnation procedure (Figure 8). The conser- native to more expensive methods. The sucro- PEG of a lower molecular mass is first added to before the treatment because PEG is soluble in vation of finds of this size usually requires the se, i.e. sugar used is white refined sugar becau- the solution, followed by PEG of greater molecu- both water and alcohol. The use of alcohol inste- construction of special hangars in which the pro- se it is less hygroscopic than brown or unrefined lar mass. The parallel method involves ad of water considerably reduces treatment time cess of conservation is to be carried out, as is sugar and will, therefore, attract less airborne simultaneously adding PEG of smaller and grea- and the finished product is lighter in both weight the cases of the two examples cited. moisture. ter molecular mass as a mixture. What is com- and colour. However, the treatment process is mon to these methods is that the PEG slowly more expensive and there is always the risk re- The drawback of the method is the length of the Wood is submerged in a bath of prepared 1 to penetrates into the wood and replaces water in lated with heating the alcohol because of its process. It is lengthy and the heating involved 5% solution of sucrose in water to which an anti- its structure. By measuring the concentration of consumes a great deal of energy and material. microbial substance and insecticide has been PEG in the solution we can determine the As an impregnation substance PEG is good at added. The concentration is increased by the quantity of absorbed PEG at any given time stabilizing wood, but it does render it darker in regular addition of set quantities of sucrose to (Figure 7). When the concentration of PEG reac- tone, heavier and gives it the appearance of ha- the solution. The addition of modest percentiles hes a level of 70 to 90% no new PEG is added, ving been coated with wax. PEG also causes (1 to 5%) is recommended until its concentration and the wood is left in the solution for a time. metals such as iron, lead, copper, bronze and reaches 50%. After that the sucrose doses are Usually, if a minimum concentration of 70% PEG aluminium to corrode. It must, therefore, not be increased to 10% until a 70% concentration is is achieved, the wood will remain stable. In so- used as an impregnation substance for wood in achieved. When the wood achieves equilibrium me cases, if the percentage of PEG in the soluti- combination with any of the cited metals with the achieved concentration of sucrose in on is more than 70%, water may be drawn out of (UNGER et al 2001, 420-422). the solution, it is taken out of the solution and well-preserved wood without being replaced by slowly dried (HAMILTON 1999, File 6). PEG, which will cause the wood to collapse. Also, after conservation and with the passage of After the wood is saturated with the impregnati- time, the elementary sulphur that is a constituent This conservation process is similar to the PEG on substance it is taken out of the vat and element in the structure of wood oxidises. Sul- method. The apparatus required is similar with gradually dried (FORS 2008, 7, 8; MALINAR phur oxidation synthesises sulphuric acid and its the difference that metal vats can be used since 2007, 105). salts, which increases the acidity of wood and sucrose does not cause metal corrosion. The Figure 8. Conservation of the remains of the wooden structure of the Mary Rose using PEG solution spraying causes its degradation. The synthesis of sulphu- wood is stable after conversion and it largely For smaller objects alcohol can be used in the (http://en.wikipedia.org/wiki/Mary Rose) ric acid and its salts is visible as a light yellow retains it natural appearance. This is one of the

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cheapest methods of wood conservation, as it artefact can be pre-treated with 10% Lyophilisation (freeze - drying) of does not entail heating the solution given that hydrochloric acid (HCl) after washing but before waterlogged wood sugar is dissolved at room temperature. The dehydration. Artefacts with a thickness of 5 - 10 Lyophilisation, or drying by sublimation, is a pro- shortcomings of the method are the length of the cm should be submerged in the solution for abo- cess of dehydrating substances by freezing process, as with the PEG method; the danger of ut four days, and artefacts thinner than 5 cm for whereby the water present within the substance a possible attack on the treated wood by insects about two days. After this pre - treatment the passes into the solid state, and then reducing and other pests; and a lack of data on the suc- treated artefacts need to be neutralised by rin- the surrounding pressure and increasing the cess of the method over a longer span of time sing them under running water for about 3-5 temperature to create conditions that allow the (UNGER et al 2001, 426-428). days. In treating the wood with hydrochloric acid, water to sublime directly from the solid to the the organic acids – which are one of the structu- gaseous state (Figure 11). Acetone - rosin method ral components of wood – break down, which The method is based on replacing the water in can improve the penetration of rosin into the This method of dehydration is used in the con- wood with a natural resin, in this case, pine rosin wood. However, hydrochloric acid can cause servation of waterlogged wood. The process is also called colophony as the impregnation subs- damage to an artefact by cracking its surface modelled to account for the fact that freezing tance. Mostly it is used to conserve well- after conservation so the pre - treatment is often water creates crystals of ice that have a greater preserved hardwoods. The rosin is insoluble in eliminated. volume than water in the liquid state, which cau- Figure 12. A freeze drier (http://www.kambic.com/ water, and is dissolved in organic solvents, the ses the degradation of the cell walls within the produkti_liofilizatorji.php) most frequently used being acetone or alcohol. The acetone - rosin method can be carried out structure of wood. To prevent this degradation For the method to be successful it is important in ethanol instead of acetone, especially if treat- the waterlogged wood is treated with a low per- treated (JONES 2003, 62; HAMILTON 1999, to use only lump, technical - grade rosin and ment is carried out in PVC vessels. Also it can centage PEG solution prior to the lyophilisation File 6). pure acetone or alcohol. be carried out at room temperature but for a lon- process. The PEG absorbed from the solution ger period to ensure the complete saturation of works within the structure of the wood as an in- This conservation method is applicable on smal- Since rosin does not mix with water it is impor- artefacts with the colophony solution. hibitor to the growth the ice crystals during the ler waterlogged wood artefacts since the pro- tant to remove the water from the structure of freezing process, and as a protection against cess is limited by the size of the lyophilisation the wood. The dehydration of waterlogged wood The advantages of the method are the stability possible changes in dimension. A 10% PEG chamber. The method can also be applied on is achieved by submerging the wood in three of the treated wood and wood that is dry, strong solution will prevent the growth of ice crystals, larger artefacts when they are disassembled or successive acetone baths. The process of and low in weight that can be easily glued and while for the conservation of waterlogged wood cut because they cannot be extracted from the dehydration in each of the baths lasts from two repaired (Figure 10). Since rosin does not react a PEG solution of at least 40% of is needed be- find site in their integral state as was the case to four days until all of the water is replaced by with metals this method can be used for conser- fore the dehydration process. The dehydration with the Bronze Age ship found in the port city of acetone. For objects of 5 to 10 cm thickness the vation when wood is present in combination with process is carried out in a lyophilisation chamber Dover in England, or with the remains of the an- dehydration process last four days, while for metal. The drawbacks are the flammability of (Figure 12) with pressure and temperature regu- cient Greek ship Kyrenia. In this case it is possi- objects thinner than 5 cm the process lasts for acetone and the high cost of the process. This lation until all the water is eliminated or until a ble to dry smaller sections, if sufficiently small, in two days in each of the acetone baths. The method is recommended for the conservation of constant mass is achieved in the wood being a lyophilisation chamber after which they are dehydrated wood is then placed in closed conta- smaller waterlogged wood artefacts of conside- reassembled (BRUNNING et al iners with a saturated solution or rosin in aceto- rable significance (HAMILTON 1999, File 6; UN- 2010, 30; KATZEV 2005, 73, 74). ne. The solution contains 67% rosin, with a 52° GER et al 2001, 399). C process temperature. This conservation is the shortest, The process of impregnati- but also the most expensive beca- on lasts from two to four use of the high cost of the device weeks, depending on the indispensable to the process. Con- thickness of the object, servation using this method can upon which the wood is only be undertaken in restoration taken out of the solution workshops that possess this devi- and the excess rosin remo- ce. ved with rags moistened with acetone. Silicone oil treatment The use of silicone oil for the stabi- In some cases, usually lisation and conservation of orga- when conserving very well Figure 10. Wooden pulley before and after conservation with acetone - rosin method Figure 11. Water phase diagram (http://eskola.hfd.hr/clanci/pahuljice/ nic materials has been conducted preserved hardwood, the (Photo: A. Jeliü; Drawing: O. G. Eibar) faznidijagram.htm) and tested for over 20 years. This

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is a new preservation technology and it should As silicone and water do not mix, water must rest, until no more oil comes out. surface with a jet of hot water or air until the be considered when choosing an appropriate first be eliminated from the waterlogged wood. structure of the wood is visible. The drying pro- conservation method. That can be accomplished using a series of An artefact cleansed of excess silicone oil has to cess conducted at specified controlled conditi- dehydration baths, starting with ethanol and be placed in a closed environment with a small ons can last for months or even years depen- Silicone oil is a collective term for any working through to several baths of fresh aceto- dish containing small volume, approximately 10- ding on the size of the artefacts (JONES 2003, polymerised siloxanes with organic side chains. ne. To make sure all water is eliminated water is 15 ml, of catalyst. A resealable plastic bag or a 71-73; SMITH 2003, 25). The basic formula is [R2SiO]n with R being an first exchanged with ethanol and then ethanol sealable plastic container can be used as the organic side chain such as methyl or ethyl. The with acetone. The length of time in each bath is closed environment. The catalyst has to be After drying, if necessary, the artefact can be silicone oil treatment is comprised of three com- dependent on the material, size and condition of exchanged every 24 hours as it has a limited reassembled. If the artefact is large or conser- ponents; a silicone oil, a cross - linker and a the artefact. Dehydration can also be done un- working life. Large objects require daily chan- ved using the PEG method the parts should be catalyst. When these three components are der a vacuum to ensure complete dehydration. ging for about two weeks; smaller objects need connected with wedges because they can hold combined a cross - linking with each other and less time. Also, everything can be placed in two large pieces or two waxy pieces together. with the cellular walls of the treated object will Once dehydration is complete, the artefact is oven heated to 52°C which will accelerate The wedges should be made of stainless steel occur creating scaffolding for the cell, but lea- transferred to the silicone oil/cross - linker soluti- catalyst vaporisation and thus reactivity with the or another strong and noncorrosive material. If ving the rest of the cell empty of bulking agents. on while thoroughly soaked with acetone. The polymer solution in the artefact. After catalysis, it the artefact is small or can be glued then the In fact, the cross-linker in this combination links solution is mixed by adding 3 - 4% of cross - is recommended that the artefact be placed un- use of cyanoacrylate glue is recommended, al- with the carbinols (-COH) in the cell structure, linker, by weight, to the silicone oil or to a der a fume hood for one or two days (LUDWICK though other types of adhesive that adhere well with the silicone oil and with itself, creating a mixture of two silicone oils with different viscosi- 2012, 11-16; SMITH 2003, 23-26). to treated surfaces can also be used. The frag- three-dimensional network inside each cell. The ties. It is often necessary to weigh down an im- ments of the artefact can be connected without catalyst in the combination speeds up this mersed artefact to prevent its flotation. This can The advantage of silicone oil treatment is in gluing or connecting with wedges. This is usually polymerisation that will fix the network in place be done with a plastic or aluminium mesh with naturally coloured and lightweight wood that is the case with the fragments of a ship. In this and provide the strength and support of the cell weights. The artefact can be kept in the solution strong enough for handling in any environment. case they are properly arranged and placed in a walls. for a long time but usually six weeks is more Dimensional changes are small and the conser- specially designed bracket in the shape of the than enough, while smaller ones require an ved wood is stable, making storage climate con- ship in question. The silicone oils are mainly silanol - terminated even shorter treatment time. Sometimes the so- trol unnecessary. Silicone oil can also be used polydimethylsiloxane polymers, and they are lution with the artefact can be put in a gradual when wood is in combination with metal becau- If cracks have occurred or if an object needs present in different viscosity from very low to and slight vacuum to speed up the acetone/ se it has no negative impact on metals. Silicone correction the gaps are filled with putty for wood. very high. Which one to use mostly depends on silicone oil solution displacement process. A oil is recyclable, so the solution can be used Araldit SV 427 with Hardener HV 427, a two- viscosity. The conservation of organic materials vacuum must be used carefully and only if the again, which reduces the long-term costs. The component epoxy resin paste for manual appli- such as wood and bone will require a silicone oil artefact is well preserved, otherwise it can cause main drawbacks are that this treatment is not cation is usually used for filling gaps but other of low viscosity. Mostly it is used as a mixture of damage and the collapse of the wood cells. With reversible and that the initial costs of materials commercial putties can be used as well (Figure two silicone oils with different molecular weight severely damaged artefacts, it is better to con- are considerable (http://nautarch.tamu.edu/ 13). and therefore viscosity. One is a low viscosity duct the displacement process at ambient pres- Theses/pdf-files/Cox-MA2008.pdf). polymer and the other is slightly thicker. This sure. At ambient pressure, acetone will vaporise way the different needs of the material being more slowly from the cells of the wood, allowing 6. Drying conserved can be provided for, for example the polymer solution slowly into the cells. After Once the process of impregnating artefacts of wood that has a soft exterior zone surrounding a the displacement process the artefact is remo- waterlogged wood has been completed they can harder and possibly structurally sound core. The ved and patted dry with a dry rag to remove be dried without dimensional changes such as lower viscosity polymer will penetrate the tight, excess silicone oil from the surface. contraction, delamination and deformation. What solid matrix of the less structurally damaged co- is important is that the drying process is conduc- re wood, while the more viscous polymer will The silicone oil/cross - linker mixture can also be ted slowly in controlled conditions. The best re- easily penetrate the softer exterior. applied topically on the surface of the artefact. sults with regard to achieving the least changes The simplest and most gentle way of applying is in dimensions are achieved at a relative humidity Methyltrimethoxysilane and isobutyltrimeho- by rolling a cotton swab dipped in the solution of 50-55%, achieved by gradual reduction from xysilane are considered as good cross - linkers onto the surface, then following with a clean 100% relative humidity, and a temperature of for this polymerisation and they are added in a swab to remove the excess. This can be done 20ºC. If the wood is conserved with the PEG small percentage to the silicone oil. Dibutiltindia- more than once on a surface for a deeper penet- method the objects are sprayed intermittently cetate is mostly used as a catalyst, and can be ration. To ensure that there is no excess in the with a low percentage PEG solution, for example applied topically or vaporised in an airtight envi- material before catalysing, it can be carefully 20% solution of PEG 4000, during the drying ronment. wrapped in absorbent paper towels and left to process. The excess PEG is removed from the Figure 13. Filling the gaps (Photo: A. Jeliü)

Conservation of Underwater Archaeological Finds - MANUAL 72 Jeliü A.: Organic Material 73

7. Drafting technical documentation ment substance from a conserved piece of um and other minerals such as phosphorous, 100% and is then changed as many times as Technical documentation should be drafted waterlogged and badly deteriorated wood. Some magnesium, sodium and carbonates. Bone is required until the soluble salt level reaches that upon the completion of conservation - restorati- of the treatment substance will chemically bond perforated with tiny canals together with a num- of fresh water. Finishing desalination with seve- on work on waterlogged wood artefacts. This with the remaining lignin and cellular structures ber of larger holes. Ivory does not have a canal ral changes of distilled water is recommended to documentation must, above all, include photog- of the wood or will simply be trapped in cellular system, but rather a layered structure caused by reduce salt to a minimum value. The level of raphs of the object prior to, during and after in- voids. Furthermore, the process of removal will growth rings. It also has a structure of very fine salts is measured using a conductivity meter, terventions undertaken, reports on laboratory cause more damage than benefit to the already tubules typical of ivory. The organic tissue of which shows the presence of all soluble salts analysis that may have been conducted and weakened structure of the wood. The both bone and ivory is ossein and it constitutes and is therefore a more reliable indicator of salt radiographic images of the object. All interventi- reversibility of an intervention should refer to the at least 30% of the total weight of the material. It presence than an individual test for a specified ons undertaken on the artefact must also be ability to re - treat an artefact that has already is often difficult to distinguish between bone and salt. described in detail, indicating all materials used. been treated, if re - treatment is necessary. ivory unless the material is examined Good documentation provides information on all microscopically. Bone is granular tissue with The removal of insoluble salts or stains is done changes to an artefact that are the result of con- Whatever the method we decide to use, characteristic pores while ivory is hard and has prior to or during desalination. It is recommen- servation-restoration work, and reduces the however – after conservation treatment the very dense tissue. Their structure is porous, ded that they be removed mechanically using number of unknown factors in any future proce- wood must be kept in controlled microclimatic which makes them sensitive to salts and impuri- picks or other tools instead of by chemical clea- dure. conditions, which is common to most conservati- ties. This structure also promotes microorgani- ning. If chemical cleaning is necessary then the on methods. The most commonly cited values sms that decompose organic substances, i.e. material must be thoroughly soaked with water The cited are only some of the known methods are a temperature of 18°C ± 2°C, a relative collagen fibres. Also in waterlogged sites, ossein before applying any chemical to prevent chemi- of conserving archaeological waterlogged wood humidity of 55% ± 2% and lighting that does not is decomposed by hydrolysis and the inorganic cal absorption and to ensure it remains on the most often implemented. The choice of treat- exceed an intensity of 200 lux (BRUNNING et al framework is disintegrated by acids, rendering surface of the artefact. The chemical cleaning ment depends on several factors: 2010, 30; HAMILTON 1999, File 6). them into a very soft material (CRONYN 1990, should be localised on the stain and done with a • The size of the object (only few laboratori- 275, 276; HAMILTON 1999, File 3). brush or swab in as many steps as are needed es are available to treat large objects or to clean the area. Calcium carbonate stains can have any kind of freeze - driers, although OTHER ORGANIC MATERIAL Bone and ivory artefact conservation be removed by using 5-10% hydrochloric or for- many laboratories have different types of mic acid, iron stains with 5-10% oxalic acid and treatment tanks); Organic materials are substances that originate The conservation-restoration process consists of sulphide stains with 5-10% hydrogen peroxide. • The degree of degradation (the varying from once living organisms, and are constructed the same phases described for the conservation When using chemical cleaning the artefact must remaining ratios of lignin to cellulose in of chains of animal protein molecules and of of waterlogged wood. The purpose of the pro- be rinsed in water to remove all residue of the wood will determine the type of treat- cellulose or other polysaccharides of plant ori- cess is to prevent physical damage to bone/ treatment chemical (HAMILTON 1999, File 3). ment); gin. By their chemical composition these subs- ivory artefacts, such as their cracking and split- • The species of wood (a very porous wood tances are organic polymers, the fundamental ting which are the consequences of uncontrolled Impregnation and drying is easier to impregnate than a non - poro- building block of which is the element carbon. In drying. They can only be cleaned, strengthened Bone and ivory are materials prone to cracking us one); general organic material is built of large molecu- and stabilised, while the need for an impregnati- and splitting during the dehydration process, i.e. • Composite objects (when wood is in com- les, i.e. complex polymers, formed by the chemi- on process depends on the level of decompositi- drying. If it is established that the osseous struc- bination with metal only particular met- cal bonding of the same or similar smaller mole- on present in an osseous artefact. Most of the ture of the artefact has been weakened and that hods can be used); cules called monomers. The chemical bonding time satisfactory restoration is impossible. dehydration could cause the cracking of the os- • The preservation of surface detail (if there of monomer molecules creates chain molecules, seous structure, the osseous artefact is impreg- are details on the wood surface one has which, bonded to one another, form microfibres. Cleaning and desalination nated prior to drying. The consolidation can be to consider which method to use) (http:// Microfibres group to form the fibres that give Bone or ivory artefacts extracted from a marine carried out in a 5-10% solution of a suitable www.kolo5200.si/conservation). organic material its sturdiness and durability environment must be desalinated to eliminate synthetic resin such as polyvinyl acetate (PVA) The substances used for wood conservation (CRONYN 1990, 238). soluble marine salts, which are hygroscopic and or Paraloid B72 in organic solvent alcohol or should also satisfy some general requirements the crystallisation of which causes physical da- acetone or toluene. The consolidant can be such as good penetration into the wood, the Bone and ivory, and sometimes leather, are the mage to non - desalinated artefacts. apply by brush to the surface several times, ea- strengthening and stabilisation of wood, the most frequent of the other archaeological materi- ch time allowing it to dry, by immersing the arte- long-term dimensional stability of wood, minimal als of organic origin conserved at our workshop. Desalination is carried out in tap water over an fact, or by immersion under a vacuum for the impact on the wooden object and the extended period with frequent changes of water. best results. Before consolidation the water has reversibility of an intervention. However, BONE AND IVORY For more important artefacts it is recommended to be removed from the artefact in a series of reversibility as a desirable aspect of the conser- that desalination be carried out gradually in a alcohol baths. The alcohol content in an alcohol/ vation process is actually misrepresented beca- Bone and ivory are sturdy binding tissues, the mixture of seawater and fresh water. The per- water bath should be gradually increased until use it is impossible to remove all of the treat- interior of which is built of collagen fibres, calci- centage of fresh water is gradually increased to the final bath is of 100% alcohol. After several

Conservation of Underwater Archaeological Finds - MANUAL 74 Jeliü A.: Organic Material 75

baths of 100% alcohol it is recommended that Leather artefact conservation The polyethylene glycol (PEG) method the artefact be immersed in two baths of aceto- Desalinated and cleaned leather artefacts are CONCLUSION ne to ensure that all the water is removed The conservation of leather artefacts endeavo- immersed in a 10% PEG 400 solution in water or (HAMILTON 1999, File 3). urs to stabilise the structure of leather and retard alcohol at room temperature. The percentage of The treatments discussed in this manual are its further decomposition. The conservation - PEG is increased every week by 10% until a used to conserve waterlogged material and ma- Bone can also be consolidated by immersion in restoration process consists of the same phases 30% solution is achieved. After a week of soa- terial from marine sites. Every artefact is diffe- a 50% solution of polyvinyl acetate (PVA previously cite for the conservation of wooden king in the 30% solution the artefact is taken out, rent and requires a different method of conser- (C4H6O2)n) in distilled water for a period of two artefacts, and those already described will not the excess PEG is removed from the surface vation, which can, to a degree, be modified. weeks. In this case total dehydration is be repeated here. using toluene or water and the artefact is With most methods, it is not a question of which unnecessary. This is followed by gradual drying gradually dried in a controlled atmosphere, i.e. treatment is better or preferred. The conserva- in a closed chamber over a period of one week. Cleaning and desalination at a temperature of 20ºC and a relative humidity tor-restorer has to be familiar with various treat- The conservation of leather artefacts begins with of 55%. Artefacts whose surface remains soft ments and be able to decide in which situation If the osseous artefact is well preserved and its the essential process of desalination and clea- even after impregnation may be subject to fur- particular treatments are the most appropriate. structure not significantly weakened, impregnati- ning. Only once the soluble salts, sediment and ther superficial consolidation by coating them After the careful study of the object it is up to the on prior to gradual drying is not required. For impurities have been eliminated the collagen with a solution of Paraloid B72 in toluene conservator - restorer to select which of the example, the bones and the ivory from the wreck fibre, which may react with other materials besi- (JONES 2003, 100). existing conservation methods to apply. The of the Mary Rose were only cleaned and desali- des water, is stabilised. decision depends on many factors such as: the nised before gradually drying at a temperature The conservation of leather artefacts using PEG desired outcome of the conservation process of 20ºC and a relative humidity of 50%. If an Leather artefacts are cleaned mechanically un- is considered a satisfactory method even though the wood should be light in colour, gluable, osseous artefact needs to be glued then a con- der a soft stream of water - soft brushes and it has been demonstrated that it is better if the flexible or rigid, insensitive to fluctuations of centrated solution of Paraloid B72 or PVA dis- sponges may also be used. In the case of persi- leather is dehydrated in a freeze drier (Figure humidity; if the wood is part of a compound persion can be used (JONES 2003, 100; ROD- stent impurities the leather may also be cleaned 12), as was the case in the conservation of leat- wood/metal artefact; the degree of degradation GERS 2004, 173). After conservation - restorati- by chemical means - the use of small quantities her artefacts from the wreck of the Mary Rose. of bone or ivory; the equipment and chemicals on treatment, osseous artefacts should be kept of non - ionic detergents (a solution of about In that case it suffices that the leather artefacts available in a workshop; the resources and facili- at a temperature of 15 to 22°C, a relative 1%) is permissible in these cases. The chemical are treated with only a 10% PEG solution over a ties available to the conservation - restoration humidity of 45 to 65% and lighting of 100 to 200 cleaning of artefacts must be followed by a tho- two - week period prior to their dehydration in a workshop. After treatment the organic artefacts lux (VOKIû 2007, 36, 59, 71). rough rinsing under a stream of water. When lyophilisation chamber (JONES 2003, 100). should be chemically stable which can be ensu- cleaning one should bear in mind that it is often red only if the artefacts are stored or displayed LEATHER better to not remove a stable impurity than to The glycerine method under optimum conditions. Otherwise they can damage the leather by the very process of clea- A frequently used method for the conservation become chemically unstable and re - treatment Leather artefacts in an aqueous environment ning (JONES 2003, 97; SMITH 2003, 62). of waterlogged archaeological leather is the could be required. Organic artefacts should, the- deteriorate over time. The water - soluble subs- glycerine method. Artefacts are immersed in a refore, be periodically inspected and evaluated tances such as tannins, fats and oils, that are a Desalination is done in tap water over an 10 to 40% solution of glycerine in alcohol or during proper storage so that re - treatment is constituent part of leather material, dissolve in extended period of time with frequent changes water for a period of two weeks. The artefacts delayed as long as possible or, if necessary, an aqueous environment as a result of which of water. Changing the water every week is re- are then dehydrated by immersion in an acetone reduced to simple and brief re - treatment. collagen fibre is rendered more susceptible to commended, as is using distilled water for the bath three times for three hours each time. Sin- hydrolysis, i.e. decomposition in reaction with last changes of water. ce glycerine does not mix with acetone it rema- The conservation method selected should be water. If waterlogged leather is dried without ins in the structure of the leather after the the least detrimental to the artefact, but also prior conservation the weakened collagen fibre Impregnation and drying dehydration process (HAMILTON 1999, File 7). satisfy the basic principles of the conservation means that there will be changes in dimension, The conservation of waterlogged artefacts may process, such as its reversibility in relation with i.e. the leather with contract. The consequence be undertaken with the aid of a number of diffe- After drying leather artefacts are kept at a tem- possible re - treatment, minimum intervention, of this is that the leather becomes very fragile rent methods. The conservators involved in the perature of 15 to 22°C, a relative humidity of 45 compatibility of used materials and that the pro- and weak and susceptible to bio-decomposition conservation of remains from the wreck of the to 65% and an illumination intensity of 100 to cess does not alter the character of the object. and the negative effects of environmental fac- Mary Rose, for example, have treated leather 200 lux (VOKIû 2007, 36, 59, 71). The right choice of method is the result of a solid tors such as light, air pollution and changes in using seven different methods. The result of the understanding of the problematics of conservati- relative humidity. Besides this, the great quantity research has revealed two methods to be supe- The successful conservation of waterlogged lea- on and many years of experience in the conser- of soluble salts that have diffused into the struc- rior in the conservation of waterlogged leather ther artefacts establishes the stability and vation of archaeological waterlogged wood and ture of the leather from the sea, besides rende- artefacts. One of these two is the polyethylene elasticity of the artefact, restoring their shape other archaeological organic materials. ring the leather hygroscopic, may also cause glycol method (JONES 2003, 98, 99). and form while not altering the chemical or abrasion to the leather (SMITH 2003, 60, 61). physical character of the leather.

Conservation of Underwater Archaeological Finds - MANUAL 76 Martinoviü I.: The Conservation and Restoration of Stone Finds 77 VIII. The Conservation and Restoration of Stone complex conservation problems, as it involves sent in the stone. numerous factors (type, quality and preservation Finds condition of the stone, the nature and intensity In microscopic analysis the procedure begins of impurity, the microclimate of an edifice and its with the taking of a sample of the marble materi- Ivo Martinoviü individual parts etc.). Around the world it is al that satisfies the conditions for analysis. This standings, whether in planning cleaning operati- customary for this work to be undertaken as an is primarily done by mechanical removal with [email protected] ons, or in carrying them out. interdisciplinary effort, by a team and for com- masonry tools or by taking a small piece of the

prehensive preparations to be undertaken in stone that originated from breakage during the "True" or primary patina is the result of natural advance of cleaning. Each case has to be ob- discovery of the artefact. The sample for and "normal" processes on the surface of stone served individually as there are no set solutions analysis is dipped in epoxy resin, which is then THE DETERIORATION OF STONE AND that occur as the result of slow physical and for individual local situations that may differ polished to a high shine. Thus prepared, the REASONS FOR CLEANING chemical processes. This produces a thin natu- significantly. stone sample is placed under a microscope and ral protective layer that, depending on its com- The most common causal agents for the deterio- photographed. The image is created by radiation position, may be of various colours. The most ration of stone are: the human factor, natural with is reflected off the sample and returns to frequent component of this layer is calcium catastrophes, climate change, soluble salts en- the initial radiation. This analysis is done to ob- oxalate, which is less soluble that mineral calcite DOCUMENTATION AND PRELIMINARY tering the pores of stone via moisture and the tain a better insight into the structure to facilitate and, as such, acts as a natural protection from ANALYSIS action of the sea and marine organisms. Stone determination of the type of stone. Once the external forces. From the scientific - technical artefacts in the sea are protected from abrupt condition has been established, the reasons for aspect it is, therefore, easy to argue in favour of Detailed documentation of the condition of stone changes in temperature or moisture levels, but cleaning and a precise objective must be estab- preserving primary patina when cleaning stone. (visual observation, photographic documentati- are, however, exposed to sea currents, corrosi- lished, i.e. the point up to which cleaning will be From the art history position it constitutes the on, the type of stone has to be ascertained – on, abrasion and the activity of marine organi- done. most significant part of the stone artefact – onto mineralogical - petrographic analysis, an sms that have a detrimental effect on stone sur- which a history has accumulated on the artefact analysis of impurities – chemical, x - ray (x - ray faces. Thus we differentiate organisms that act or ancient building in the aesthetically most valu- diffraction), microscopic analysis) has to be un- chemically and mechanically, destroying the DESALINATION surface of stone (algae, sponges, bacteria, mol- able form. In contrast, impurities are a layer of dertaken prior to cleaning. Samples for mineral - accumulated calcification, encrustations of mari- petrographic analysis can be chiselling off, dril- luscs etc.). Besides the detrimental effects of Stone that has lain in wet soil or the sea for an marine organisms, we also know of the detri- ne organisms, various types of discolouration led out with a core bit or by the removal of spal- that occur when stone is in contact with other led flakes of stone (MALINAR, 1998). This extended period of time was wet with water that mental effects of soluble salts on stone, contained greater or lesser quantities of soluble especially in situations when a find is taken from materials (iron, bronze etc.) and compounds that analysis establishes the type of stone of which occur as the result of the aggressive action of the artefact is made and its geological age. This salts. Having been brought to the surface, the the sea to land. The drying of the stone leads to stone begins to dry. With the escape of moisture the crystallisation of the detrimental soluble salts sulphates, chlorides and nitrates. Before under- can ascertain with a high level of certainty the taking cleaning the origin and composition of stone quarry from where the stone originates. through pores in the stone and its evaporation we find in seawater – primarily sodium chloride into the atmosphere, soluble salts remain on in large quantities, while potassium chloride, impurities and their possible detrimental effect Samples for chemical analysis are taken in the on stone must be ascertained. A decision then same manner as sampling for mineralogical- and under the surface of the stone. As the stone magnesium chloride, calcium sulphate and mag- dries out they accumulate here and crystallise. nesium sulphate are found in small quantities, needs to be made on whether to clean the stone petrographic analysis. Chemical analysis deter- of encrustations and, if so, in what manner and mines the chief components of the stone. Semi- The critical moment occurs when the size of the but may also be detrimental to the "health" of crystals achieve the size of a pore. New stone. to what level. Cleaning is directly associated quantitative x-ray analysis of soluble salts in sto- with the conservation of stone, as the consolida- ne are carried out with the evaporation residue quantities of salt coming from the interior of the stone to the surface increase the size of existing Besides this "health" - related reason for clea- tion of a damaged surface sometimes needs to of the aqueous extract of salts from stone using be effected prior to cleaning, while often the true X - ray diffraction. This is an exceptionally useful crystals. Crystallisation pressure, which now ning stone, the aesthetic reason is equally im- exceeds the hardness value of the stone, begins portant. Encrustations of marine organisms co- state of an artefact, i.e. the level of damage, can analysis as it determines the types of salts pre- only be determined after cleaning. The choice of to destroy its structure. This is manifested as ver fine details in the surface, and with the accu- surface crumbling, sloughing or the delamination mulation of thicker encrustations, details are lost cleaning method depends on many factors: the type, quality and condition of the stone, the na- of entire crust sections. The salts in stone may from view. Thus at times the natural relationship be of diverse chemical origin. By type of anion, of indented (shadowed) and protruding (lit) sur- ture and intensity of impurities, the size and type of stone surface (a straight façade, a simple ar- the most frequent salts are from the sulphate, faces is altered. chloride and nitrate groups. Sulphates may origi- chitectural decoration and a valuable sculpture demand different approaches). nate from a polluted atmosphere or as It is very important to note the fundamental diffe- windborne aerosol; nitrates may originate from rence between impurities and patina. The impre- Figure 1. Microscopic image of a sample of Proconnesi- The cleaning of stone is one of the most soils; and chlorides most often from the sea, but cise use of these terms often leads to misunder- an marble (Photo: I. Martinoviü) may also be found in continental areas where

Conservation of Underwater Archaeological Finds - MANUAL 78 Martinoviü I.: The Conservation and Restoration of Stone Finds 79

they are contained in the soil. of eliminating detrimental soluble salts is by che- stone causing damage. und particles with coarse surfaces (NIKŠIû, mical procedures, such as the process of con- 2004). As a result dirty surfaces are cleaned in a There are several ways in which salts can verting harmful calcium sulphate into insoluble Washing, i.e. moistening, stone with water vapo- much gentler fashion than with "classic" abrasi- successfully be removed from stone material. barium sulphate. This is the Lewin method of ur, known as nebulising, is done with a fine ve cleaning in which the abrasive is crushed The most widespread procedure used for small treating stone with a solution of barium spray of water under high pressure (100 bar) rock or sand with sharp-edged grains. The dry fragments is desalination by submersion. Water hydroxide. using a system of pipes and sprayers that keep procedure is now increasingly used as it provi- in the bath enters the pores of the stone and the rock wet over an extended period of time, des for easier control of work and avoids gradually dissolves soluble salts. The dissolved without excessively wetting it, until such time as unnecessarily wetting the stone, but does salt is extracted into the water by diffusion, while CLEANING WITH WATER the impurity has soften sufficiently to be remo- require special conditions (use of a mask by the clean water continues to penetrate the stone ved with light brushing. operator, the isolation of the work area). Becau- and dissolve salts. This goes on until a balance Cleaning water may be tap water, but distilled or se of the complexity of the operation and its is achieved between the concentration of salt in deionised is better (DONELLI, ŠTAMBUK- This is usually achieved by time control of the relatively slow pace, this procedure is used the desalination bath and the concentration of GILJANOVIû, 2004). Large quantities of water washing (four seconds of wetting followed by a primarily for the cleaning of sculptures. salts in the stone. When this balance is achie- are undesirable for a number of reasons (the four minute dry interval). The impurity is presence of iron, polychrome, the risk of dirtying, progressively softened to the point where it can There are several ways in which abrasive clea- the loss of fragile material, the problem of the be removed with a brush. ning is controlled: by the hardness, shape and migration of salts and the penetration of water, fineness of the abrasive grains; air pressure, the the danger of freezing). Washing with pressuri- blast nozzle aperture diameter; the distance of sed water is not recommended on sensitive sur- CLEANING WITH ABRASIVES the nozzle from the surface of the stone; the faces, especially where architectural plastic, angle of the stream in relation to the stone surfa- sculpture and the like are present, and where Abrasive cleaning mechanically removes the ce. the stone surface has been damaged, where layer of impurity, but besides removing dirt it stone is crumbling off and where erosion has also tends to destroy the natural patina of stone occurred. Pressurised steam is sometimes used, that protects its epidermis, which is sometimes CLEANING WITH COMPRESSES especially in the removal of greasy impurities. damaged and softened. After abrasive cleaning Care must be exercised in the process, as the the epidermis is exposed to accelerated damage Cleaning with compresses is used especially steam may rapidly heat up the surface of the caused by reactions with detrimental compo- when salts have to be removed from stone, or Figure 2. An example of desalination by submersion in a nents of the atmosphere. Often sandblasting when the impurities are difficult to dissolve and vat (Photo: I. Martinoviü) itself damages this soft epidermal layer. Abrasi- need to be kept in contact with the solvent for an ve cleaning also destroys traces of the dressing extended period, and then drawn out. Compres- ved the procedure is halted. The salty water is of the stone, and rounds edges. In the ses are made of absorbent materials that are taken out and replaced with new clean water. exceptional cases when abrasive cleaning is mixed into a paste. The most frequently used Monitoring of the procedure is conducted by approved, it must be performed by a highly spe- are: specialty clays – sepiolite, attapulgite, diato- quantitative chemical analysis, by measuring pH cialised person who must have a good maceous earth, talc and chalk, non-acidic binder values, and by measuring the electrical knowledge of why cleaning has been underta- such as scrap cotton or paper pulp and bread conductivity of the aqueous extract. Another pro- ken and in what measure it is to be effected. (MALINAR, 1998). Because of their three- cedure involves the coating of the stone with The cleaning of complex architectural decoration dimensional (porous) structure these materials various compresses made of a porous powdery and sculpture is done separately, as a restorati- are able to absorb water up to 1.5 times their or fibrous material soaked in water. This may be on operation with somewhat different, i.e. more own weight, without changing in volume. The a mash of cellulose fibres or paper, attapulgite, precise techniques. This refers to micro abrasive most frequently used medium (binder) in com- sepiolite, or clay, kaolin, stone dust and the like. blasting. Abrasive procedures can be wet or dry. presses is water, although other solvents are Water from the compresses first enters the sto- The level of abrasion, i.e. the possibility of effec- also used. The principle by which they work is ne and dissolves salts there. As the compresses ting control, depends on several factors: the har- that the medium (reagent) softens the unwanted dry out the moisture evaporates, drawing salts dness of the abrasive, the shape and size of the substances on the surface of the stone and out to the surface where they remain. When the particles, the pressure, i.e. speed at which the draws them into the mass of the compress while compress is saturated with salts, it is removed particles hit the surface and the width, distance the cleaning substance evaporates from the ou- and replaced with a new clean compress. The and angle of the stream. The abrasive used can ter surface. The compresses may additionally be desalination process is monitored by chemical be harder than stone (aluminium oxide – corun- covered with plastic film to retain moisture and analysis of the salts both in the saturated com- Figure 3. Cleaning with pressurised water (Photo: M. dum is the hardest at 9 Mohs), and is by compo- prolong the cleaning action. Compresses of sla- presses and in the stone itself. The third method Mustaþek) sition pure calcium carbonate, shaped into ro- ked lime clean the surface of limestone by the

Conservation of Underwater Archaeological Finds - MANUAL 80 Martinoviü I.: The Conservation and Restoration of Stone Finds 81

combined action of mild alkalinity and softening beyond the visible part of the spectrum, usually are as a result very fragile, can be carefully clea- by moisture. Mora AB-57 paste is a mild chemi- at a wavelength of 1,064 nanometres. Lasers ned with a laser, without prior consolidation. cal compress, very effective in cleaning limesto- used for other applications emit in the ultraviolet ne and marble. Its ingredient EDTA facilitates range, i.e. in the visible part of the spectrum. Laser can be used to remove impurities of the the dissolution of calcium salts. The compress There are currently in Europe some ten types most diverse origin: black encrustations formed contains: ammonium bicarbonate, soda bicarbo- that differ in terms of the source of light, by deposition from a polluted atmosphere, biolo- nate,EDTA (ethylenediaminetetraacetic acid), wavelength, emitted energy and duration of im- gical layers (mosses, lichens, algae), sediments carboxymethyl cellulose and disinfectant, all dis- pulse. of movable dirt, prior surface treatments, corrosi- solved in water. Monumentique is a paste similar on layers and impregnated stains (graffiti). to Mora's paste in which the chief ingredient is Cleaning lasers consist of three main compo- Experimentation is also being done on the clea- also EDTA and that is marketed as a finished nents: a generator, the cooling system and the ning of polychromes, using different parts of the product under the names Monumentique paste laser unit. The beam is transmitted via an articu- light spectrum (ultraviolet, visible light) or S and Monumentique paste C+ polymer. lated arm with mirrors or a fibre optic delivery significantly shorter impulses. The desired clea- system. An articulated arm allows for the tran- ning effect is achieved by the targeted choice of smission of high - power beams, while optical wavelength, energy density (fluence) and impul- CLEANING WITH CHEMICAL AGENTS fibres allow for a regular beam cross - section, se duration. which is important when working with sensitive Chemical agents for cleaning stone are usually objects where a low energy density is used. An The advantages of laser cleaning are that there used when other procedures have failed, optical fibre also allows for the transmission of a is no contact, that it allows for direct and precise especially when impurities have penetrated dee- laser beam over greater distances (tens of met- control, that the procedure is selectivity - self- p into the pores of stone. This procedure can res), which is practical when working on edifices, limiting, ecologically clean and complementary. entirely remove natural patina, but also some as there is no need to move the device along The chief drawbacks to laser cleaning are: limi- soluble components of stone, which weakens its scaffolding. tations on thick scum, on counter conical relief surface structure. Sometimes chemical procedu- Figure 4. Cleaning using the cavitation method (Photo: I. surfaces, and the cost and lengthy duration of res combine two cleaning agents (acid and ba- Martinoviü) Laser emits an intense, pure form of light in a the process in relation to other methods. se) with the idea that they will neutralise one very short interval. When the pulsing light is di- another. However, a reaction may occur ir condensation creates a cavitation vacuum) on rected at a stained surface, the foreign, impure Laser cleaning preserves the total layer of seve- between them creating salts within the pores of the surface of the stone, which separates a cal- material significantly absorbs the energy, crea- ral microns that constitutes the patina, and stone. The salts crystallise and swell in the pro- cite crust from the surface of stone. ting a photomechanical effect. When the light thereby the natural protection of the stone. Unli- cess exerting a pressure of about 1,000 atm. In impact is very short (in an order of magnitude of ke in all other cleaning techniques, degraded chemical cleaning methods it is impossible to The cavitation method allows for very precise several nanoseconds), there is insufficient time stone surfaces – at times very unstable – do not control the depth of the penetration of chemicals work in separating a crust or various discolurati- for the heat to pass to the substrate. The result require prior consolidation when undertaking into stone, or the reaction of chemicals and sto- ons on the surface of stone, causing no damage is that impurities are freed and ejected from the laser cleaning, moreover, it would be unfavoura- ne. In conservation practice the rule is that all to the surface of the stone in the process. The surface, leaving the substrate untouched. As a ble as it would retard the action of the laser. This materials that are applied to the surface of stone drawback of the method is its slowness (only result the removal of impurities using laser can advantage of the laser is significant, as a conso- must be inert and reversible. small surfaces can be treated) and, as such, it is be described as self-limiting. This means that lidant can attach some of the impurity to the sto- not recommended for large objects. the removal of material from a historical substra- ne and thereby render cleaning more difficult. te is stopped as soon as the impurity has been Likewise, if polychrome is present on the stone, CLEANING USING THE CAVITATION removed. Even artefacts that have been impac- prior consolidation could bond part of the pig- METHOD CLEANING WITH LASER ted by advanced deterioration processes, and ment to the impurity and thereby prevent discri-

The cavitation method is borrowed from Laser cleaning is the latest procedure in which dentistry and is used to remove thin calcite de- laser beams of a given frequency react upon the posits. The principle upon which it works is that dark colour of impurities, creating resonance in the surface that is to be cleaned is sprayed with them and converting them into fine dust that is a fine stream of water while the tip of a pin or removed as smoke. Laser is an electromagnetic fine spatula vibrates at a very high frequency. wave, like all light, but monochromatic (NIKŠIû, This vibration creates a cavitation effect (the 2004). Each laser has a characteristic sudden evaporation of water in bubbles and the- wavelength. A laser used to clean sculptures emits in the range close to infrared radiation, Figure 5. Joining, and the positions of inserted stainless steel rods (Photo: I. Martinoviü)

Conservation of Underwater Archaeological Finds - MANUAL 82 Martinoviü I.: The Conservation and Restoration of Stone Finds 83

they leave when dressing stone in order to ren- state and that it preserves the artefact as such der the reconstructed surface as close as possi- from further deterioration. ble to the original artefact.

CONSERVATION

With regard to impregnation, i.e. the protection of stone from the effects of moisture, the at- mosphere and other detrimental substances, Figure 6. Stone wheel before, during and post-treatment (Photo: I. Martinoviü) there is a broad range of protective materials minative cleaning. If a very degraded and unsta- extent possible, eliminate undesirable collateral and application methods. A decision on a type of ble stone surface is revealed upon cleaning, its effects. protective material and the method of its appli- consolidation should immediately be underta- cation depends mostly on the type and condition ken. of stone and on the conditions the stone artefact BONDING AND RECONSTRUCTION will be kept in following conservation - restorati- Finally, it should be noted that the laser is a on work (JAKŠIû-BIZJAK, 2010). Stone protecti- technology that is quickly assuming an ever mo- As artefacts are for the most part found in a fra- on substances differ in their chemical compositi- re important role in conservation - restoration gmented state, they require gluing and the re- on, newly formed products, effectiveness of pro- practice. Laser is not a universal cure; it is only construction of missing sections in order to res- tection and durability. It is very important that one more technique that can be successfully tore the artefact, in the greatest measure possi- materials for the protection of stone allow water applied in combination with other cleaning and ble, to its original condition. and vapour to pass, that they create a barrier to conservation techniques. external influences, that they are compatible Epoxy resin and adhesives based on polyester, with the petrographic and physico - chemical The great diversity of methods is accounted for, to which fillers are added depending on the type characteristics of stone and that they have as on the one hand, by the great number of diffe- of stone (marble dust, talc, finely ground limesto- little as possible impact on the appearance of rent situations present in practice, and on the ne etc.), are primarily used when gluing, i.e. the treated stone artefact. other, by the desire to avoid the negative effects bonding fragments. The speed of adhesion of each of the cleaning techniques is inevitably glues based on polyester can be regulated by accompanied by. For example, all methods that the addition of accelerators and catalysers. CONCLUSIONS involve the application of large quantities of When joining larger fragments gluing is aided water are not recommended because of the di- with the use of serrated non - corrosive Cultural monuments, because of their importan- rect or potential damage they can cause through (stainless steel) pins/rods. ce to the human community, require particular massive infiltration into the stone substrate, not care and very high financial expense to be pre- to mention the impossibility of working in cold Depending on the type and condition of stone, served for future generations. Many of them ha- weather. The threat of abrasive methods – inclu- reconstruction is effected with diverse materials ve, over the centuries, from their creation to the ding micro sandblasting – to the original surface and the use of various tools. Acrylic emulsions present, suffered various forms of damage and of a stone artefact is well known, and this met- are used with additives of stone dust acting as contamination. Each of the methods cited has hod is thus used only when all others have been fillers, polyester and epoxy resins (also with the advantages and drawbacks. Some allow for the exhausted. Chemical methods in general have addition of an appropriate filler), various mixes of relatively speedy treatment of large stone surfa- two drawbacks: on the one hand the likely infil- white cement, stone dust, slaked lime etc. When ces, while others are very slow. Some require tration of unnatural substances into the stone reconstructing stone finds we can also fabricate significant human interaction, some less. When mass with varying degrees of harmfulness, and a "patch" of true stone when we are able to de- undertaking conservation - restoration work on on the other, the necessity of rinsing these com- termine the type of stone with certainty. stone monuments the chief criteria for the choi- ponents out with large quantities of water. "Patching" with true stone is done by finely trim- ce of method is: that it must not be harmful to ming the stone with masonry tools and then glu- stone, i.e. that it must not cause damage to the As a result it is natural that people involved in ing it to the original find. It is important to diffe- stone or create secondary products that may stone cleaning try to identify the negative rentiate among traditional masonry tools cause damage. The purpose of conservation - consequences of individual methods, and work (martellino/mason's hammer, bushing chisel, restoration work is to restore the appearance to find new ways that could, to the greatest tooth chisel etc.), i.e. to recognise the traces and condition as close as possible to the initial

Conservation of Underwater Archaeological Finds - MANUAL 84 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 85 IX. The Handling, Packing, Transport and Storage of a team of appropriate experts will be based on these decisions. In this phase the conserva- of Underwater Archaeological Finds tor must secure adequate materials for packing and transport and make preparations for the Tanja Perin, Anita Jeliü of first aid for finds and are very important in stabilisation of extracted finds - vital to the pha- ensuring that finds are delivered to specialised ses that follow as it will reduce the detrimental [email protected] institutions in an unaltered state, where the fur- effects of extraction. It would be ideal if an ther course of conservation procedures will be experienced conservator diver were present at determined. Proper storage prior to complete the site during the entire underwater research INTRODUCTION conservation procedures, known as passive sto- effort to provide advice and determine further rage, is necessary to stabilise the object and steps in our actions, treating the objects and the The conservation of archaeological underwater maintain it in the same state in which it was deli- site as a whole. The presence of a specialised Figure 2. Drafting documentation at the site (Photo: I. finds is not limited only to the process of an vered from the find site, while proper storage conservation expert during the actual extraction Miholjek) object's active stabilisation in specialised labora- after conservation is necessary to ensure the of the object is tremendously important - proper tories or workshops - conservation and conser- long term stability of treated objects - the treatment will ensure the long - term stability of tion of a set of criteria that includes financing, vators themselves should be involved in all pro- exhibition of conserved objects in inadequate the object. Intervention during research depends the project's feasibility, whether the object will ject phases; from preparatory examination and conditions may lead to deterioration and the ac- on whether a decision has been made to leave ever be exhibited, i.e. whether an adequate site the extraction of the object, right up to and inclu- tivation of undesirable processes. the objects and the site in situ, or if there are for exhibition and storage exists, and what evi- ding the final exhibition of the object to the gene- plans to undertake the extraction of finds. Rea- dence is gained by extraction that could not be ral public. In underwater archaeology conservati- sons for extracting an object must be defined in procured through in situ observation (CRONYN on is not just a collection of specific procedures HANDLING UNDERWATER advance, before any kind of excavation and the 1990, 44). The determination of a plan and pro- and treatments - conservation also provides us ARCHAEOLOGICAL FINDS extraction of objects to the surface, and they cedures to be implemented will depend above with answers to important questions concerning must weigh considerations of the possible detri- all on the fragility, significance, location, size our history. It is the task of every conservator to Major and irreversible damage may be done if mental consequences extraction may cause. and mass of the object, the goals of the project, care for the preservation of an object's integrity objects are handled in an inadequate fashion in the available time, the available sources of fi- as an important piece of historical evidence. the early stages of research, resulting in the loss LEAVING OBJECTS AT THE SITE (IN SITU) nancing and the possibilities of further conserva- of significant information, which may affect the tion (BOWENS 2009, 154). The following section will discuss the proper further stages of the object's conservation. It is, Moving objects alters the integrity of the site and handling of objects and the need for special therefore, important to pay a great deal of atten- it is, therefore, of the outmost importance that Every effort must be made during extraction of techniques and guidelines that reduce the tion precisely to proper procedures towards ob- detailed documentation be kept so that the his- an underwater archaeological find to ensure that possibility of damaging objects to the lowest jects at the site, and the further handling of a torical significance and the integral context is not the object is preserved and that it retains its possible degree. The proper handling of finds find after it has been extracted from its natural lost. In many cases the wisest course of action integrity. At all times we should bear in mind the includes the procedures applied at the find site environment. When discussing the proper han- is to leave the site untouched to allow future ge- fact that these are exceedingly fragile objects itself, during the extraction of the find, dling of objects we need to keep in mind the co- nerations the opportunity to study it. If a decision that appear much sturdier than they actually are. immediately following extraction on the surface urse of an entire underwater research effort, has been made to leave the objects at the site, and during transport. All of the procedures and because the handling of objects will differ in the thereby preserving its integrity, measures must The first step in any underwater archaeological guidelines that set out proper handling are a sort various phases of a project. be taken to prevent its further deterioration and research where a decision has been made to possible looting. bring finds to the surface is to draft detailed do- The first phase of research includes all of the cumentation. Photographic documentation of the preparatory work whereby data is collated perta- HANDLING OBJECTS DURING EXCRACTION position of every find must be made, and of their ining to the site and the objects present. This is TO THE SURFACE orientation with regard to one another. If possib- a key phase, as it provides a complete picture of le a video record should also be made, and the site, which will determine the further course Bringing objects up to the surface is a very every find should be numbered. Numbering is of the research. Preparatory examination is es- complex operation that demands detailed plan- important so that the relationship between indivi- sential, as the information retrieved will determi- ning for the safety of all participants of the rese- dual finds and the site can be determined later ne the significance of the site and of individual arch effort. Before making a decision to extract a in the laboratory. For marking purposes the most finds and a possible decision to extract individu- given object, especially a large one, research frequently used are plastic boards or film on al objects. The essential prior preparation of must be undertaken that will, in the final tally, which designations are written with water resis- containers for the short - term and long - term answer the question of whether extracting the tant markers or labels made using a Dymo devi- Figure 1. Drafting documentation at the site (Photo: M. object is beneficial. This must include considera- ce. Finds should also be sketched at the site Marukiü) storage of extracted finds and the organisation

Conservation of Underwater Archaeological Finds - MANUAL 86 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 87 using plastic board and pencil. The sketch sho- must be provided with the appropriate support. uld show the positions of finds at the site and Various means can be used to provide support, state the distance between the finds and control from simple straight wooden or plastic boards to points at the site. specially constructed supports whose form follows the shape of the object. Given the great number of various situations we may encounter during underwater archaeologi- When raising very long and fragile, but relatively cal research, it is difficult to provide a description light objects we use a plastic support onto which of procedures for every specific situation or the object is transferred and then fixed by bin- every individual object. What follows, therefore, ding it with strips of textile. Because of the is an overview of the most frequent situations we length of these object using several balloons is encounter when extracting underwater archaeo- recommended to provide balanced lift in as hori- logical finds (FELICI 2002, 203-215; BOWENS zontal position as possible. 2009, 154-156). In the case of fragile ceramic finds, especially if Small objects they are fragmented, one of the methods is im- Before being raised to the surface, small objects mobilisation in plaster directly at the site. The are placed in net receptacles, usually plastic find and the surrounding material is sheathed in baskets, which can be pulled by rope onto the nylon or aluminium foil, then a layer of cotton boat or lifted by a single diver when full enough. wool and finally wrapped in gauze or jute. A bag Figure 4. Extracting a bronze cannon (Photo: R. Moskoviü) If the objects are very small they are placed in Figure 3. Extracting amphorae using air balloons (Photo: of plaster is emptied on the wrapped find and self - adhesive bags or plastic canisters that can R. Moskoviü) the resulting block is simply transferred to a bag be closed shut. Fragments of a single artefact extraction to the surface. In the case of individu- or basket and raised to the surface. are also placed in self - adhesive bags or seala- filled, therefore, the air in it expands as it rises al finds, amphorae may be raised using a cord ble plastic canisters. This way they are stored and the lift increases, which results in an uncon- from the deck of a ship - if this is the case great Very effective techniques have been developed apart from other finds. If the object is sufficiently trolled and very rapid ascent to the surface. The care should be taken to properly attach them to to raise wooden and metal finds where there is a sturdy it can simply be wrapped in bubble wrap balloon may lose its buoyancy, which results in the rope, i.e. it is important that they are raised great danger of their imminent breakup. Depen- or in polyethylene film and raised to the surface. the fast return of the object to the seabed. By with the neck facing upwards, avoiding the use ding on the shape and size of the object a sturdy using several smaller balloons, a loss of of the handles as fixing points. Heavy and large finds buoyancy may occur in one balloon while the Before undertaking any heavy lifting, the vessel buoyancy of another will remain the same. Most Dolia, as a particular type of earthenware contai- and lifting devices should be tested to determine balloons have a vent control that a diver can use ner, are placed in sturdy nets that are then rai- stability for safe operation. Heavy and large to release air to control the speed of the rise. In sed using cranes on a ship's deck. finds can be raised in several ways. They can this manner a single diver can lift quite large be lifted using a winch or endless chain hoist if objects (GREEN 2004, 268-274). When raising anchor stocks it is important to the ship or the platform is directly over the site or bind them well with rope so that they do not bre- by a hand - operated trailer that can be installed To be able to visualise heavy and large finds we ak under their own weight while being raised. on board a ship. Financially more acceptable can take the example of amphorae, lead or sto- Noteworthy as particularly difficult are very long solutions, however, are to use a cord from the ne anchor stocks and cannons. In the case of and fragile objects, where simply binding them deck of the ship or to lift with the aid of air - filled amphorae particular care should be given to well with rope will not suffice. The appropriate balloons. There are many commercially availab- their contents, and amphorae must under no support must be secured prior to their extraction. le air balloons of varying sizes. They can be circumstance be emptied at the site, and should A wooden receptacle within which the object is used to raise cargoes ranging from several hun- rather be extracted with their entire contents, as fixed is most often used for this purpose. dred kilograms to several tonnes. The basic it is from them precisely that important informati- principle on which these balloons function is to on will later be gained. When faced with a site Fragile finds inflate the balloon until full and the maximum lift with a large number of amphorae the best met- In the case of very fragile finds we need to provi- is achieved. When possible it is better to use hod of extraction is to arrange the amphorae in de the appropriate support prior to raising as several smaller balloons rather than one large the vertical position in a metal basket sheathed they could break under their own weight or water one. This is because the air in the balloon in a material that will prevent the amphorae from pressure. With these finds we need to proceed Figure 5. Excracting Apoxymenos from the sea in a metal expands as it rises. If the balloon is only partially hitting into one another or moving during with the outmost care. Prior to extraction they crate (Photo: D. Frka)

Conservation of Underwater Archaeological Finds - MANUAL 88 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 89 base is prepared that is subsequently encased the Swedish ship Vasa. The principles applied in were treated using standard conservation proce- ment and includes all of the actions taken by a with lead leaf onto which a layer of cotton wool that case were later successfully used with other dures. conservator or other professional staff during is placed. The object is placed on this layer of similar finds. The procedure involved excavating temporary storage and transport to a specialised cotton wool and itself clad in cotton wool. tunnels under the ship's keel through which laboratory in which active and permanent con- Everything is additionally fixed into place by en- heavy cables were then drawn and affixed to STABILISING EXTRACTED OBJECTS servation of the find will be conducted. casing them in lead leaf that, because of its pontoons placed above both sides of the sunken pliancy, simply adapts to the shape of the ob- vessel. Water was then pumped into the ponto- Extracting an individual object disrupts the natu- A key element in this stabilisation process is to ject. ons until their decks were level with the surface ral equilibrium achieved between the object and ensure that every object is maintained in the of the sea. When water was then pumped out of its environment. At the moment of submersion same or almost identical conditions to those it The remains of ships the pontoons the Vasa began to rise from the every object is exposed to the intense influence was extracted from the moment it leaves the The remains of ships and of various other craft bottom. The procedure was repeated several of the surrounding environment, which includes water. The following are the chief guidelines to should certainly be mentioned as a separate times and the Vasa was literally pumped out of chemical reactions with water and the soluble follow at the site when handling freshly extracted category of underwater archaeological find. The- the water. A floating construction was built aro- salts present, colonisation by fungi and algae, underwater finds (BOWENS 2009, 153; KAR- se finds are very interesting because ships, und it within which the Vasa floated to the muse- and erosion caused by sand. Extended STEN 2009, 20-22): when they sink, are a sort of time capsule and um where further conservation was undertaken exposure to these factors leads to the significant together with their entire contents become a and where it was accessible for viewing by visi- degradation of the object. A natural equilibrium • Objects must be kept submerged or wet witness to their time. It is impossible to give a tors. The success of this procedure in the case is achieved after a time between the object and the entire time. Drying may have catas- universal rule when extracting the remains of of the Vasa was contingent on the relatively go- all of these environmental factors, which results trophic consequences for objects as it ships because the procedure will vary from case od condition of the wood, a fact related to condi- in a relative halt of the decomposition process. causes surface cracking, breakage and to case depending on the dimensions, structure, tions in northern seas. the growth of moulds, which may lead to age, location, level of preservation and the This natural balance is disrupted upon the the complete destruction of the object and possibility for its housing after extraction. When dealing, however, with very fragile wood excavation and movement of the object. very quickly reduce it to a pile of dust. The that could easily break under its own weight the Exposing the object to a new set of conditions objects are best kept in water from the If the wood is in very poor condition any attempt above cited method cannot be implemented. In initiates a chain of physical and chemical reacti- original location, or in a mixture of the to extract the ship in one piece would result in a these cases the weakened structure must be ons that can in the end lead to the complete de- original water and freshwater, or in complete breakup, and the best solution is to provided with an appropriate support that will struction of finds. The chief causes of accelera- freshwater in the case of very stable and extract individual pieces. In these situations it is adapt to the shape of the ship's structure. This ted deterioration are visible light, UV radiation, sturdy objects. of the outmost importance that comprehensive method of extraction was used in Marseilles du- changes in temperature and relative humidity, documentation is drafted and that every piece ring the extraction of the remains of Greek ships insects and inadequate transfer, transport and • Objects must be stored in suitable inert be carefully marked so they may be reassem- from the ground. Wooden beams were placed storage (CRONYN 1990, 69-70). containers.Polyethylene vessels, boxes bled as a whole later during treatment. horizontally under the remains of the ships until and bags are suitable containers for the a platform of sorts was achieved, which was The chief task of the person handling finds, storage of freshly extracted finds. Within The extraction of the remains of a ship in a sin- then raised together with the remains. When ideally a conservator, upon extraction is the sta- these containers objects can be gle piece has been undertaken successfully in faced with cases like this of very fragile finds bilisation of finds to prevent their deterioration. additionally stabilised and secured using some cases, the best known such case is that of there is another recent technique that was This process must begin immediately after the protective layers of foam or sandbags. employed to extract the wooden re- object has been taken from its natural environ- These containers must be sealed mains of the Sea of Galilee boat in hermetically to prevent the evaporation of Israel. Layers of resin were applied the solution in which the objects are pla- along the entire length of the boat, ced. about 8 m long, until a sturdy casing had been achieved. Canals were • Objects must be sorted by their compositi- also dug under the keel of the ves- on. Finds are usually stored in plastic sel, into which resin was also injec- bags, plastic nets and plastic boxes with ted until a sturdy support bracing or without covers based on their composi- was achieved. The resin dried in the tion. This is particularly important when air and the entire block, encasing the dealing with metals, since storing two dif- wooden remains, simply navigated ferent metals together creates a galvanic the lake. After being delivered to the effect between them leading to corrosion. processing site the resin was remo- If finds from different period – usually ce- Figure 6. Raising the Vasa to the surface (http://www.vasamuseet.se/ Figure 7. A graph of the decomposition process over time (http:// en/The-Ship/Life-on-board/) ved, and the remains of the boat ramic finds – are found at a site it is re- www.nps.gov/museum/publications/MHI/AppendI.pdf)

Conservation of Underwater Archaeological Finds - MANUAL 90 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 91

commended that they be stored • Objects must be shielded from direct sun- adhesive polyethylene bags, special bub- ted in a single container to preserve the separately according to their particular light. Increased exposure to light causes ble wrap materials and boards of integrity of the site. These objects must periods. It is also recommended that frag- photochemical reactions, changes to colo- expanded polyethylene foam have been be separated from one another, either by ments of the same object be stored toget- ur and the fading of the surface, accelera- shown most appropriate to this function. individually wrapping them in polyethylene her but separate from other finds. Organic tes the speed of decomposition and pro- film or by using special plastic partitions materials should also be stored motes the growth of algae. Upon • Objects must at all times be kept wet to and should be additionally immobilised to separately and by their composition. extraction objects should be kept in the prevent them from drying out, especially if stop them from hitting one another. dark as much as possible. transport to a storage facility lasts several • Objects must be adequately tagged. Sto- days. Objects are wrapped in textile that • In the case of exceptionally fragile and red objects must be appropriately tagged • Objects must be secured. Weapons and is thoroughly soaked in water and then sensitive materials it may be necessary to and catalogued. To this end we must use potentially explosive materials should be additionally wrapped with film to reduce fabricate a made - to - measure support of a system of tagging that will remain stable handled with care and pursuant to the the evaporation of the liquid. wood or polyethylene foam to provide in the conditions in which an object is safety guidelines prescribed in a given them with adequate support and protecti- temporarily stored. Two methods of tag- country. In Croatia the Weapons Act • For a long transport period, i.e. up to two on. ging that have proven to be stable in (Official Gazette 63/07, 146/08) is months, objects wrapped in soaked textile aqueous solutions are plastic ribbons im- currently in force. should be placed in three layers of • The packing must keep the object clearly printed using a Dymo device and writing polyethylene films, which are checked for visible to avoid the need to unpack it du- on plastic labels or containers using water leaking, and then well - sealed with pac- ring transport. resistant markers which will not fade away PACKING FINDS FOR TRANSPORT kage sealing tape. Afterwards, the objects with time. If using solutions that dissolve are wrapped in two to four layers of bub- • Objects must be properly tagged - double Dymo labels or plastic markings, we can To avoid the possible damaging of finds during ble wrap and placed in cardboard cartons. tagging is recommended, i.e. one tag in use non - corrosive metal labels. If a label transport to a place of temporary storage or to a the packing or container and another on is tied to an object, i.e. the handle of a laboratory where conservation will be underta- • If the transport time to the storage site is the outside. pot, an inert twine, like polypropylene, ken, a great deal of attention must be paid to short, the objects need not be additionally must be used for securing, as cotton proper packing. The packing method must pro- wrapped to prevent evaporation, rather • At no time should wet archaeological arte- twine will rot. Labels tied on wooden sam- tect against shock and vibration, while at the finds are sprayed and covered in layers of facts be allowed to freeze. ples should be tagged using stainless same time the find should be protected against polyethylene film to keep them wet. steel pins because staples or pins made drying. Even slight drying can cause saturated • It is important to know that underwater of other metals will corrode. For objects and near-saturated marine salts, including calci- • For ferrous and cuprous metals it is re- finds, especially in the case of organic placed inside a plastic bag, plastic net or um sulphate and calcium carbonate, to deposit commended that they be immersed in a materials, dry out quickly and all of the plastic box, labels should also be put insi- within the artefact, leading to surface damage. reducing solution, i.e. 5% sodium carbo- procedures cited above are intended for de the bag, net or box. When using a pla- Several factors need to be taken into considera- nate or 2% sodium hydroxide, before pac- transport only and should by no means be stic box it is also recommended that the tion when packing, above all the distance a find king to slow their further corrosion. used for longer storage. Finds should be box also be labelled. Labels should state is to be transported and the place where the find deposited in the precisely stipulated con- the name of the archaeological site and is to be stored. For most artefacts it stands that • Besides proper packing, organic material ditions provided in the following section 5 date of excavation, and also with other they should spend at least 24 hours in mixture of should be refrigerated to slow the rate of on passive find storage immediately site-relevant information such as 50% original salt water and 50% freshwater be- biodeterioration caused by microorgani- following transport. quadrant, stratigraphic unit and depth and fore packing for transport. Also the material used sms during transport. a description of the object. for wetting an artefact during transport should be soaked in same mixture. To ensure the • Transporting finds in containers filled with PASSIVE FIND STORAGE • Objects must be kept cold. A rise in tem- maximum possible protection during transport water should be avoided, as objects may perature increases the speed of decom- we should follow these guidelines when packing be carried by the movement of water in Passive storage is defined as a method of safe position, promotes the growth of fungi and (BALLARD 2008, 78-80; BOWENS 2009, 154- the container, which may lead to damage. storage of extracted archaeological finds that moulds and activates corrosive reactions 156, JONES 2010, 10): If finds are transferred in such containers, should prevent the further deterioration of an in metals, which again has as its they should be so arranged as to prevent object until active conservation is undertaken at consequence the visible damaging of the • All materials and containers used for pac- any movement and impacts between ob- a specialised laboratory. These storage facilities object or a weakening of its structure. Ob- king and additional means of immobilising jects. would ideally be situated close to a find site to jects must, therefore, be stored in as cool an object must be of chemically inert ma- allow for immediate storage in optimal conditions an environment as possible upon terials. Polyethylene canisters with lids, • Several objects of the same composition immediately following extraction. The following extraction, ideally in a refrigerator. various polyethylene wrapping films, self- that form an ensemble may be transpor- are the minimal conditions these storage met-

Conservation of Underwater Archaeological Finds - MANUAL 92 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 93 hods and facilities must meet (JONES 2003, PASSIVE STORAGE OF METAL FINDS Gold, silver, lead, tin and their alloys entirely submerged is economically very unfeasi- 35): Further corrosion of these metals after extraction ble, and in these cases the only alternative is to • Deterioration should be stopped or redu- While they may appear to be very solid and in has not been observed, i.e. exposure to atmosp- use spraying. It has been demonstrated that the ced to the smallest possible measure du- good condition metal finds, iron especially, are heric conditions does not affect them. As a re- best results are achieved when spraying water ring passive storage. very often highly unstable and it is, therefore, sult these finds do not need to be stored in a cooled to a temperature between 2 and 5°C. very important that metal finds be stored in stab- water-based solution but may, rather, be dried • The storage method applied should in no le conditions immediately upon extraction to pre- and stored until their active conservation. If the- Wooden finds may be stored temporarily in con- way affect further conservation procedu- vent active corrosion (BOWENS 2009, 157-158; re are significant deposits on an object it is good tainers filled with water. Plastic canisters with res. JONES 2003, 48-49). to keep it in a 5% solution of sodium lids are used for smaller finds, while specially sesquicarbonate or sodium carbonate in water fabricated polypropylene or polyethylene contai- • Containers used in passive storage must Iron to prevent the deposits from hardening before ners with covers to prevent the penetration of be easy to maintain. Objects must be The extraction of iron finds accelerates the cor- they are removed (JONES 2003, 48). light are used for larger finds (BOWENS 2009, easily accessible to specialised staff while rosion process because of the change to envi- 156-158; JONES 2003, 36-47; BRUNNING in passive storage. ronmental conditions, above all the available PASSIVE STORAGE OF ORGANIC FINDS 2010, 20; SINGLEY 1981, 8). amount of oxygen, percentage of moisture and • Finds must be accessible to the general the presence of chlorides. To control these con- In ideal conditions the temporary storage of or- In many cases temporary storage becomes long public, especially if the finds are of great ditions iron objects must be stored in tap water ganic finds should be as brief as possible before - term, which may lead to the degradation of significance or of high interest. to which a corrosion inhibitor has been added their active conservation. However, this kind of wood resulting from the postponement of active immediately upon extraction. The most temporary storage very often lasts for years until conservation and stabilisation treatment. Temporary or passive storage will differ based frequently used corrosion inhibitors in this type funds and conditions are secured for appropriate on the kind of material a find is composed of. of passive stabilisation are sodium hydroxide, treatment, especially for larger wooden finds. sodium carbonate and sodium sesquicarbonate. The basic conditions for the storage of organic PASSIVE STORAGE OF CERAMIC, GLASS Water solutions to which these substances have finds are as follows: AND STONE been added will prevent iron corrosion as long as the solution's pH value is maintained above 8 • They must be kept in a 100% moisture During the passive storage of ceramics, glass and up to 12. For short-term storage, which sho- level the entire time. and stone it is important to control soluble salts uld not exceed six months, a 5% solution of so- • Exposure to light must be kept to a mini- by controlling relative humidity. Relative humidity dium carbonate (pH 11.5) is used, or a 5% solu- mum to prevent the development of alge. must be kept high (100%) to prevent tion of sodium sesquicarbonate (pH 9.7). For • The growth and development of bacteria, crystallisation of salt; otherwise formed crystals long term storage the best results have been fungi and pests must be prevented or re- can cause physical damage. Finds made of the- achieved with a 1% solution of potassium dic- duced to the minimum possible level. se materials must be stored by submerging hromate in water to which sodium hydroxide is Figure 8. Improper storage of a wooden find has cau- them in containers filled with water. After added until a pH value of 9 to 9.5 is achieved. Passive storage of wooden finds sed it to dry out and crack accompanied by the extraction these finds must under no circumstan- When working with these kinds of solutions the Small wooden finds can be stored wrapped in growth of mould on the surface ces be immediately submerged in tap or deioni- toxicity of chromate presents a major problem polyethylene bags or film, with the addition of a (http://www.english-heritage.org.uk/publications/ waterloggedorganicmaterials/waterlogged-organic- zed water, but rather in seawater, which is then and they need to be handled with the outmost minimum quantity of water, and the thermal bon- materials-guidelines-draft.pdf) gradually replaced with tap water over a period caution and only by a professional (HAMILTON ding of the ends to prevent the entry of air. The of several weeks. This kind of wet storage ensu- 1999: File 9, 10-13; JONES 2003, 48). packed object is then placed in a further two Passive storage of bone and ivory res the stability of the object over an extended polyethylene bags to prevent the loss of water. It Artefacts made from these materials must be period of time - the only thing required is to un- Copper and its alloys has been observed that this method of storing stored in freshwater to prevent the crystallisation dertake regular monitoring and changes of the As with iron the process of corrosion is rapidly keeps finds from drying out, but does not pre- of salts, which often cause physical damage. water to prevent the growth of biological organi- accelerated upon extraction because of the dis- vent microbiological activity. The only way to They also have to be stored at a low temperatu- sms. Also, during extended storage of glass the ruption of the equilibrium achieved. These ob- reduce microbiological activity in finds thus sto- re of 2-5ÛC and the water must be changed on a pH of the solution gradually begins to rise which jects are, therefore, also passivated by deposi- red in polyethylene bags is to treat the wood regular basis with possible control of microbiolo- can be harmful to glass. Buffers can be added to ting them in a 5% solution of sodium with biocides and storage in a cold place, ideally gical activity (JONES 2003, 48). keep the pH down, as can bactericides to pre- sesquicarbonate or sodium carbonate in water. a refrigerator at 4°C. In the case of very large vent damage from bacteria (CRONYN 1990, This kind of storage is recommended for no lon- wooden finds, such as wooden ships, a major Passive storage of leather finds 137; HAMILTON 1999: File 4, 1-2; JONES 2003, ger than 6 months prior to desalination and acti- problem during passive storage is preventing During the passive storage of leather the loss of 48-49). ve conservation (HAMILTON 1999: File 12, 2; them from drying out. Constructing large contai- water must be prevented and the conditions JONES 2003, 48). ners in which these types of finds would be must be as similar as possible to those from

Conservation of Underwater Archaeological Finds - MANUAL 94 Perin T., Jeliü A.: The Handling, Packing, Transport and Storage of Underwater Archaeological Finds 95 which the find was extracted, which means that Containers that serve for transportation should expansion or contraction of materials, which organic underwater archaeological finds is 45- they must be kept in controlled conditions of protect finds against external influences such as may cause permanent damage to an object. 65%, while for wooden finds only the range sho- temperature, pH, salinity and microbiological temperature, relative humidity and light on route Elevated temperatures lead to photochemical uld be within the narrow boundaries of 55-58% activity. Keeping leather finds wrapped in to the destination. The type of container used for reactions that may result in the fading of colours. (JONES 2003, 117-119; VOKIû 2007, 14-16). hermetically sealed polyethylene film or in sea- transportation is selected based on weather Permanently elevated temperatures in combina- led containers is recommended to prevent conditions, the length of transport and the me- tion with high humidity values promote the deve- LIGHT drying out, and at a temperature of from 2 to 5° ans of transport. Usually a wooden containers lopment of fungi, bacteria and insects. Keeping C to reduce biological growth. In case of signifi- for longer transport and cardboard boxes for the temperature in areas in which objects are Objects, especially those of organic origin, are cant biological activity we can use quaternary short distances. It is recommended that tran- stored or exhibited between 18 and 20°C is re- sensitive to exposure to both visible light and to ammonium salt as a biocide, with copious rin- sport containers not be overly large or heavy commended (JONES 2003, 117-119; VOKIû UV radiation, which cause them to undergo vari- sing of treated finds using deionized water while transporting. It is also recommended that 2007, 14-16). ous photochemical changes. To prevent the de- (BOWENS 2009, 157-158; JONES 2003, 47). these containers have handles for easy han- terioration of finds during exhibition or storage, dling. In means of transport such as a lorry RELATIVE HUMIDITY finds should ideally be stored in darkness, i.e. (truck) it is essential that containers be secured exhibited in strictly controlled lighting conditions. TRANSPORT AFTER CONSERVATION in order to prevent their movement during tran- Inappropriate relative humidity is considered the For ceramic, glass, stone and metal the lighting sport. leading cause of the deterioration of objects. should be under 300 lux while for organic mate- After conservation finds are usually transported Humidity can be inappropriate in three cases: if rial lighting should not exceed an intensity of 50 to the owner, museum or some other facility. In the case of large and clunky finds they are it is too high, too low or if there are significant lux. Given that the detrimental effects of light on Before transportation finds should be properly also packaged separately. Finds must be pro- fluctuations in relative humidity. objects are cumulative, it is recommended that packed and secured. Packaging finds before tected from all sides either with bubble wrap, objects be returned to a dark place or that the transport and unpacking after transport should sponge or sponge - like material, and then fixed • If relative humidity is constantly above premises be kept dark when a museum is not be carried out very carefully. This should be to the base, in a manner that makes them easy 70% it will significantly accelerate biologi- open (JONES 2003, 117-119; VOKIû 2007, 14- handled calmly, deliberately and systematically. to handle. The shocks that are present during cal activity, which will result in the appea- 16). transportation and the vibration of means of rance of mould and fungi, lead to the cor- Finds are packaged separately; they should be transport cannot be completely avoided, but the- rosion of metals and to dimensional chan- BIOLOGICAL ACTIVITY wrapped in paper – acid - free paper is recom- ir harmful effects can be reduced and alleviated ges on objects, especially those of orga- mended – and then be placed in polyethylene with proper packaging. nic origin. Finds in storage or part of an exhibition in a mu- bags, bubble wrap, or smaller boxes made of seum must be constantly monitored for possible plastic, wood or cardboard depending on the • Relative humidity constantly below 40% insect or rodent attack or the possible growth of find. Several separately packaged smaller finds PERMANENT FIND STORAGE leads to significant structural changes in fungi, mould and bacteria. Biological activity is are packed together in larger boxes, and then in objects of organic origin. controlled by the above-cited microclimatic con- shipping containers. It is important that the pac- Once the process of the active conservation and ditions, which must be kept in precisely defined kaging is done systematically, that the packaged restoration of finds has been completed and on- • Significant and sudden oscillations in rela- boundaries (JONES 2003, 117-119). material from one site does not interfere with ce, if necessary, they have been transported, tive humidity will cause dimensional oscil- material from another site unless otherwise no- they must be stored in the appropriate conditi- lations in organic materials. ted. Systematisation is possible within material ons, irrespective of whether a decision has been CONCLUSION from the same site, and then according to their made to store it in a depository or to exhibit it in To ensure the long - term stability of finds relati- composition. a museum or similar facility. The object has be- ve humidity must be kept within precisely defi- This section has endeavoured to present the en stabilised by the conservation process, but ned boundaries. In general, keeping relative basic guidelines we must adhere to when han- Every empty space inside packed boxes or con- we need to bear in mind that only the regulation humidity at a level ranging from 40-70% with dling underwater archaeological finds, both at tainers for transportation must be filled in order and constant control of the storage conditions maximum variations of ±2% is recommended. the site and following the extraction of finds. The to avoid shock and vibration during transportati- will provide for long-term protection. The microc- The recommended value of relative humidity for importance of proper handling during the tran- on. Foam materials are used for filling – usually limatic conditions that require strict control to ceramic, glass and stone is from 45-65%, except sport of finds has been emphasised with the aim sponges, bubble wrap, foam, paper etc., as this ensure the long - term stability of materials are in the case of unstable glass. In that case the of ensuring the integrity and stability of extracted fixes all material in place and prevents slipping temperature, air humidity, illumination and con- relative humidity should be between 15 and objects prior to their active and complete conser- during transport that could lead to mechanical tact with detrimental materials and substances. 40%. For metal underwater finds relative vation. The last section cites the conditions for damage. "Fragile" or "Handle with Care" labels humidity should be constant, with a value of the permanent depositing and storage of finds - should be affixed to containers or some other TEMPERATURE about 40%, although for iron the recommended only proper procedures and storage in appropri- indication that the material must be handled with value is 15% and 35% for copper and its alloys. ate conditions, after a find has been completely the outmost care. Fluctuations in temperature may lead to the The recommended range of relative humidity for conserved, can ensure its long term stability.

Conservation of Underwater Archaeological Finds - MANUAL 96 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 97 Proper management of finds is vital - adequate X. In situ Protection of Underwater Cultural handling at the site and immediately following extraction serves as a sort of first aid for finds Heritage and guarantees that they are delivered in an unaltered state to the institution at which they Mladen Pešiü with the aim of the best possible and longest will be adequately stabilised and protected from [email protected] lasting solution for the preservation of our herita- the inevitable and rapid onset of further deterio- ge. ration.

INTRODUCTION

WHAT AFFECTS THE DEGRADATION In situ protection refers to the concept of preser- AND CHANGES TO IN SITU OBJECTS ving underwater cultural heritage at its original site, regardless of whether it is on land or The formation of individual archaeological sites underwater. There are many reasons why the in under water is the result of the sinking of land situ protection of underwater sites should be sites, individual objects or artefacts. Once an given preference as the first option, above any individual find or site is placed in this new envi- invasive activities directed towards the research ronment it becomes subject to various physical, of underwater cultural heritage. We can only chemical, biological and mechanical factors: the underline that the process of the conservation infiltration of water (sea) into the object's structu- and restoration of underwater archaeological re, the effects of oxygen and chemical reactions finds is a costly and demanding job and that, as in water, corrosion, the effects of various marine a rule, the process is never completed as a re- organisms, algae and bacteria, erosion, the se- sult of the tendency of archaeological finds to dimentation of sand, hydrolysis and other fac- continue deteriorating. Another reason is a de- tors, depending on the actual surroundings in arth of exhibition space in museums, which is which the object is found. frequently the reason why archaeological finds sit forgotten in depots. After a time, however, there is a relative stabili- sation of degradation processes in an aqueous The rules of in situ protection emphasise the environment, and it can be said that the process importance of, and respect for, the historical of an individual object's deterioration has - owing context of a cultural object, its scientific signifi- to the agency of physical, chemical and biologi- cance, the importance of preserving underwater cal factors - attained a relative stagnation, more cultural heritage for future generations and pre- precisely - that it is significantly retarded. There venting the mistakes that have been committed are, however, factors that may still effect chan- in the past to the detriment of underwater cultu- ges to the stability of a site or artefact that has ral heritage as a result of the improper handling attained this level of stability. This pertains abo- and care for cultural objects. In situ protection ve all to the destructive activity of people whose also stresses that cultural objects, under normal work is tied to the sea and the seabed, such as circumstances, have achieved a certain level of treasure hunting, sports diving, fishing, stability owing to low rates of deterioration and underwater construction works, dredging oxygen levels, and are, as such, in many cases (MANDERS 2012, Unit 9.10), and to various not threatened. If threatened, of course, there is natural factors that constantly (sea currents, ti- a need to protect these sites, but again in these des and waves, marine organisms) or cases, preference should be given to various intermittently (natural catastrophes) have a ne- non-destructive methods and the methods of in gative effect on underwater heritage. situ protection that will be discussed further in the text. Given the truly high level of diversity among the classes and types of underwater si- tes, each of them requires an individual approa- ch to protection, conservation and presentation

Conservation of Underwater Archaeological Finds - MANUAL 98 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 99

Convention sets out the rules that pertain to acti- pulation and the historical and archaeological building up fine sediment such as sand, it may THE LEGAL PROTECTION OF vities directed towards underwater cultural heri- value of the site. The second parameter pertains happen that it does not manage to stabilise at UNDERWATER CULTURAL HERITAGE tage. It includes practical and applied regulati- to the conditions affecting the site and influen- the site before being carried away by sea cur- ons that should be adhered to when undertaking cing its survival or degradation, among which we rents. Various kinds of barriers may be used

excavations, provides guidelines on how to de- may number physical, biological and chemical with the purpose of improving and increasing the Throughout history most underwater cultural sign research and preservation projects and em- factors. The third parameter pertains to the pos- duration of the depositing of marine sediments, heritage was protected from human activity by phasises the qualifications researchers should sibilities for and feasibility of in situ protection, thereby expediting the process. These may be the inaccessibility of the underwater environ- have to undertake activities related to the pre- and the financial framework on which a final de- low bulwarks set perpendicular to the direction ment - sites located at greater depths, as a rule, servation and management of underwater cultu- cision concerning the protection of a given site of the movement of underwater currents that enjoyed a greater chance of being preserved. ral heritage. often depends. It is on the basis of the study of serve as barriers along which broken off algae The development of professional diving these parameters that we can determine the and seaweed is deposited, facilitating the depo- equipment opened access to these locations to Another key factor alongside the legislation pro- methods and strategies that will be implemented sition of sediments (STANIFORTH 2006, 53). the wider public, which increased the danger of vided by individual countries in preserving to protect and conserve the site or, perhaps, to Methods of implanting artificial seagrass at a site their devastation. This development demanded underwater cultural heritage is the cooperation present it in situ in the form of a museum. are being perfected of late with the purpose of of the professional community that it develop of competent authorities charged with its care. In exploiting the sediment that moves with water legal measures and regulations that will help Croatia, for example, this pertains to the princi- When dealing, for example, with the remains of currents. Since natural seagrass does not take preserve underwater cultural heritage. Countries pal cultural institution - he Ministry of Culture - a wooden ship structure on the seabed one of well to replanting on the sandy bottom once dis- adopted legislation that encompasses the legal and to conservation departments, museums and the methods of burying with sand would be ide- turbed, artificial grass is used in its place to en- protection of underwater cultural heritage with institutes and other competent institutions al. For a Roman period shipwreck with the rema- courage the deposition of sediment. Certain more or less success. A few of the noteworthy whose cooperation with the police and port aut- ins of a large number of amphorae implementing conditions have to exist at the site for this kind of acts in effect are the Historic Shipwreck Act in horities aims to create favourable conditions for protection by the use of a cage would be an ap- protection to be effective, notably an optimal Australia, The Protection of Wrecks Act in Great the best possible organisation of the protection propriate solution, while for a large modern sun- depth, a relatively flat bottom and regular and Britain, Portugal's legislation on marine and of underwater cultural heritage. Furthermore, ken vessel legal protection and presentation in optimal currents. Without a relatively strong sea underwater archaeological heritage or Croatia's one should not disregard the potential of diving the form of an archaeological park would be the current there is not enough moving sediment to Cultural Property Protection and Preservation clubs and local populations, whose interest sho- suitable method of protection. Further in this be deposited, and accumulations form on the Act and its Ordinance on Archaeological Rese- uld be that underwater cultural heritage is pro- section we shall elaborate the most frequent artificial grass that prevent its movement and arch. The lack of harmony among these laws tected, all with the aim of preserving it for future methods of physical protection with examples of sediment gathering, whereby it loses its purpo- prompted professionals to draft and adopt a sin- generations, and for the development of the sites at which they have been implemented. se. An example of the ineffective use of this gle regulation to treat the protection of economic and tourism potential that may arise method is at the Legare Anchorage shipwreck underwater cultural heritage. The 1996 ICOMOS from the proper care of underwater cultural heri- COVERING THE SITE WITH A LAYER OF site in Florida (SKOWRONEK et al. 1987, 316- Charter for the Protection and Management of tage. SAND AND STONE 317), while a positive example is the protection the Archaeological Heritage was a key step in of the wreck of the William Salthouse in Australi- formulating an international legal framework. As a result of the natural processes present on a (STANIFORTH 2006, 54). There are also This was followed by a 2001 session of UNES- the seabed underwater sites are often covered examples of when, as a result of the natural CO when the body adopted its Convention on THE PHYSICAL PROTECTION OF in sand during their formation, which creates a conditions and strong sea currents, this kind of the Protection of the Underwater Cultural Herita- UNDERWATER CULTURAL HERITAGE physical protection barrier above them. protection has not proven effective enough to ge and the Annex to that document. The Con- Exceptional situations may, however, uncover create a stable environment for the site, and vention laid out the fundamental principles for Various methods of physical protection safegu- and expose a site. The phenomena that create a other methods also had to be implemented for the protection of underwater cultural heritage, ard sites from physical damage and to a certain threat to these sites are most often natural chan- effective protection, as was the case at the provided a framework for cooperation between degree may limit the damage caused by natural ges such as strong waves, currents and natural Hårbøllebro site in Denmark (GREGORY et al. countries and expounded the rules that relate to factors. When selecting a method of protection catastrophes and only sometimes are they rela- 2008, 17-18). activities directed at underwater cultural herita- we must take various parameters into considera- ted to human activity. The principle of repeated ge. The Convention also established some basic tion, unique to each site. The first parameter protection is very straightforward - exposed finds Another application of the sand burial method is principles such as the obligation to preserve pertains to the general characteristics of the site are covered in a layer of sand that has the pur- a customary practice in underwater archaeologi- underwater cultural heritage, encouraging in situ itself: the type of site (harbours, shipwrecks, pose of securing the site from visual and cal research. Upon the completion of every ar- protection as the primary method of preservati- structures, buildings, artefacts and human rema- physical contact with external factors. The effec- chaeological research campaign there is a need on, opposing commercial exploitation, and pro- ins, objects of prehistoric character, aircraft), the tiveness of this method may be limited because to protect excavated areas. Covering already moting information sharing and professional trai- predominant type of material at the site (wood, of the possibility of a repetition of the process excavated trenches with sand ensures the pro- ning with the aim of raising public awareness of ceramics, metal, glass), the depth at which it is that was the initial cause of the destabilisation of tection of this part of the site, and also provides cultural heritage preservation. The Annex to the situated, the level of threat to the site, its state of preservation, its accessibility to the general po- the site. There is also the problem that when us with reference positions for the continuation

Conservation of Underwater Archaeological Finds - MANUAL 100 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 101

hion should be subject to monitoring and regular the finds in an anaerobic environment, which supervision. The method of covering a site with contributes to stabilising archaeological material. sandbags has been implemented successfully at This method, of course, is not appropriate to a number of sites such as at the Solway wreck every site and a set of conditions have to be in South Australia (CORONEOS 2006, 55-57), present to warrant its implementation. This per- Duart Point in Scotland (MARTIN 1955, 19) and tains, above all, to the strength of the sea cur- at several sites in Italy (DAVIDDE 2004, 143). rent and the quantity of sediment available. Be- cause the eyes of the netting through which COVERING THE SITE WITH CANAVAS OR sand is to pass may be blocked by the growth of POLYPROPYLENE NETTING algae and other marine organisms that tend to colonise the netting, this method is limited in its This method involves installing fine mesh can- application to appropriate sites. Nevertheless, vas or polypropylene netting over a threatened regular monitoring of the processes at a given Figure 1. A complex method for the burial of a site using natural and artificial materials (NEGUERUELA 2000, 112) site with visible surface finds on the seabed so site and timely intervention can address most of that the netting is not taut, but rather gently mo- the problems that arise during the sedimentation of research during the next archaeological cam- followed by a polypropylene netting, a layer of ves with maritime currents (Figure 3). process. This very effective and inexpensive paign. Covering parts of a site is often associa- gravel and sand, metal netting fastened to the Polypropylene netting has been demonstrated method of protecting sites has been used in pla- ted with the use of geotextiles; textiles made of bottom with spikes, followed by heavier stones as superior in this application because of its gre- ces like Sri Lanka on the wreck of the Avondster polypropylene or polyester fibres. Geotextile and the camouflaging of the entire area with se- ater strength and longevity. To keep it in place (MANDERS 2006a, 58-59), in the Netherlands needs to be installed at the site prior to burial in agrass (Figure 1) (NEGUERUELA 2000, 112). this netting needs to be weighed down or affixed at the Burgzand Noord 10 wreck (MANDERS sand to isolate the researched area of a site This creates an artificial hummock, incorporated to the bottom, usually with sandbags or spikes 2003, 18-20; MANDERS 2006b, 72) and at the from the deposited sand. This is very important into the natural surroundings and protected from along the edges. Over a short period of time site of the Hårbøllebro wreck in Denmark to avoid the contamination of the site by the looting and unwanted visitors. (one to a few weeks), as a result of the activity (GREGORY et al. 2008, 19-22). secondary deposit whereby the geotextile is sta- of sea currents and waves, fine sand enters the bilised above the finds, and to avoid the OVERING THE SITE WITH SAND BAGS eyes of the netting and accumulates over the COVERING THE SITE WITH A CLOSED BOX unwanted disturbance of archaeological strata. site. Over time this creates an artificial emban- This method of temporary protection has been This is a method of protection used at sites kment over the site. This is a very interesting protection solution that proven inexpensive and beneficial in archaeolo- where there is strong erosion, mostly as a result may also be used during archaeological rese- gical practice (DAVIDDE 2004, 142). of various natural processes, and where the sim- This buries the site in a layer of sand, protecting arch, and upon its completion is a basis for long pler method of depositing a layer of sand would it from the actions of waves, sea currents and term in situ protection. The system of covering a not provide long - term protection. This method marine organisms (shipworms, mussels, fish) site with a closed box is an in situ site protection of physically protecting a find or site involves the and human factors. This system shields the site principle that consists of several steps. A perma- use of polypropylene bags filled with sand (bags from the view of potential looters and also keeps nent metal frame that surrounds the area we of organic materials have a shorter life span). The bags are arranged at the site with the aim of entirely covering it up, providing physical protec- tion (Figure 2). The sandbags are able to resist the water current and may mitigate the effects of wave action on the site. They are most effective when installed in greater numbers, densely pac- Figure 2. Part of a shipwreck near Oruda island, Croatia ked so that their edges overlap. They should be protected with sandbags (Photo: R. Moskoviü) placed on the seabed in as low a profile as pos- sible to allow the water current to flow gently If there is a need, besides with sand, the site over them, since arranging them in the form of a may also be covered with a heavier aggregate hillock could have the effect of destroying fringe (gravel, rock), taking care not to damage archa- areas of the site by the action of sea currents eological finds in the process (BOWENS 2009, (BOWENS 2009, 168). Covering a site in san- 167). There are a number of variations to this dbags cannot be considered a lasting solution, method of protection. The most complex method since the bags in which the sand is packed will involves burying the site with a layer of sand, deteriorate over time - sites protected in this fas- Figure 3. Protecting a site using polypropylene netting (MANDERS 2008: 36)

Conservation of Underwater Archaeological Finds - MANUAL 102 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 103

the necessity arises. Another problem is that, and to see to the upkeep of the cage, which is, since the netting is usually installed directly abo- besides, in the club's best interest. This approa- ve the site, potential looters can quite easily cut ch has achieved a level of site self-sustainability, the protective netting and devastate a site. This as it provides benefit not only to the responsible method of protection is most effective if combi- diving club but also to the local community. The ned with some other method such as burial with shortcoming of this method is the limited lifetime sand or sandbags. This method of protection is of the netting, estimated as some twenty years - frequently implemented in Italy (DAVIDDE 2002, continued materials and degradation inhibitor 83-84; DAVIDDE 2004, 143-144) and in Croatia development may extend their useful lifetime (JURIŠIû 2006, 154-155). (JURIŠIû 2006, 155-156). This model of protec- tion has been implemented in the Croatian Adri- PROTECTIVE CAGES atic since 1990 - eight sites with the remains of shipwrecks have been protected to date. These This method has as its purpose the physical pro- are Roman period shipwrecks with a large num- tection of a site achieved by covering the entire ber of integrally preserved amphore. Their signi- Figure 4. A site that is protected with a closed box (NEGUERUELA 2000, 115) site with protective cages. A cage consists of a ficance and level of preservation make them sturdy metal structure onto which steel netting of ideal examples for this type of physical protecti- wish to protect is first installed on the bottom. an archaeological site by impeding undesirable various sizes is affixed and joined. This method on (ZMAIû 2009, 18-19). Metal plates are then affixed to the frame on its access to archaeological finds. Galvanised iron of fabrication allows us to create a cage of the vertical and horizontal sides. These plates are nets, additionally coated in corrosion inhibitors, desired size, depending on the size of the area moveable, and may be removed during research are installed over a site to provide protection we wish to protect. The cage is attached to the allowing archaeologists to study the area under (Figure 5). The netting has to be affixed to the seabed and additionally weighed down with con- them. This structure is useful during research as bottom with spikes, or weighed down with con- crete blocks to ensure its stability (Figure 6). The it also provides a working surface on which hand crete blocks to ensure they remain fixed in the top of the cage has locked openings for authori- tools may be placed, divers are able to navigate desired place. sed persons providing them with direct access to it safely and it also prevents damage to those finds with the purpose of further documentation parts of the site still covered by other parts of Marine organisms will quickly colonise the net- or find maintenance. Protective coating is appli- the structure. At the end of research and docu- ting and they will be completely overgrown in a ed to the nets to retard corrosion, as are zinc mentation the space between the finds and the relatively short period of time, creating visual protectors in the role of sacrificial anodes to pro- metal structure is filled with sand to stabilise the protection of the finds we want to safeguard. vide cathodic protection of the cage (MESIû finds, and the plates are fixed to the metal frame And while this kind of in situ protection is 2008, 96). Their purpose is to corrode before the Figure 6. A protective cage over a Roman period shipwreck to completely close the site and finds, which are inexpensive and ideal for very shallow sites, it steel cage, increasing its life span. An info plate off the island of Žirje, Croatia (Photo: M. Pešiü) left in situ. The box is then covered in successi- should not, because of certain shortcomings, be is affixed to the cage providing basic data on the ve layers of sand, protective netting and stones. considered a final solution. The greatest site and providing a further aspect of legal pro- A grassy covering may also be installed, which drawback of this method is the fact that the net- tection as it indicates that the site constitutes IN SITU CONSERVATION AND protects the site and blends into the site's natu- ting corrodes quite quickly, and requires protected cultural property. The examples of STABILISATION ral surroundings (Figure 4). Covering a site in systematic monitoring and replacement when protection cited so far have aimed to conceal this fashion is most effective for shipwreck finds sites from the public and thereby protect them With the development of the conservation- and ship structures that form a smaller, closed from external influence. Protective cages, restoration profession and the application of context, and that require longer, systematic and however, have a different role in that they serve knowledge from other branches of science, so- precise documentation. The closed box protecti- to present the site. A site thus protected offers me methods that have been applied primarily in on system has been successfully implemented the broader diving community the possibility of other fields have made their way into the practi- on a Phoenician vessel from the 7th century BC accessing underwater heritage without posing a cal in situ protection of archaeological sites. in Spain's Mazarron (NEGUERUELA 2000, 112- threat to its safety. There are legal regulations in Their goal is to act directly upon the stabilisation 116). place to govern protected sites in Croatia. The and retarding of degradation processes in targe- competent ministry issues a multi - year conces- ted archaeological objects. One of these is cat- PROTECTION USING METAL NETTING sion to interested diving clubs who lead groups hodic protection, applied only on metal finds. of tourists to a site. The club in question under- The principle upon which the method is based is Protective metal nets are usually used as takes the obligation to carry out frequent monito- that the object we wish to protect (the cathode) Figure 5. The Mijoka Shallows site off Murter protected with physical protection from an immediate threat to metal netting, Croatia (Photo: I. Miholjek) ring of the cage to prevent undesired visitors is placed into electrical contact with a sacrificial

Conservation of Underwater Archaeological Finds - MANUAL 104 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 105

ce of certain artefacts has made burial in sand and preservation (BERGSTRAND et al. 2005). one of the frequently applied methods of protec- ting already researched archaeological material (BERGSTRAND et al. 2005, 9). MUSEUMS AND PARKS IN SITU

The purpose of this method is to store archaeo- Once archaeological material is extracted from logical material in a stable environment to retard the water and undergoes conservation- physical, biological and chemical deterioration. restoration treatment it is exhibited in museums Once research and documentation has been and collections specialised in caring for this kind completed, archaeological materials are arran- of material. Of late there is a growing tendency ged in a trench prepared in the seabed and buri- towards presenting underwater cultural heritage ed in sand - alternatively, a special structure is in situ in the frame of underwater archaeological fabricated for the same purpose (Figure 7). Cer- parks or underwater museums. The presentation tain standards must be observed in the process, of cultural heritage is closely linked to, and an the most important of which are that the objects inseparable component of, archaeological finds, must constantly be kept in a wet environment and it is important that a person involved in the during documentation to prevent their deteriora- protection of heritage is knowledgeable in the tion, that each object must be properly tagged basics of presentation. Furthermore, because of prior to burial to facilitate the work of those who the constant tendency for archaeological materi- will one day access the material again. The pur- al to continue deteriorating, the conservator- pose of this procedure is that the reburied mate- restorer must be familiar with the conditions and rial achieves a stable condition providing for methods of preserving objects and to be in a many years of storage, until the need arises for position to act in a timely fashion towards their its extraction and restoration (DAVIDDE 2004, preservation. We shall look here in brief at a few 139; ORTMANN 2009, 11-13). This method is of the methods of presenting archaeological applied for the most part on wooden ship struc- finds related to underwater archaeological heri- tures the conservation and restoration of which tage. Figure 7. Sketch of a hummock with buried wooden elements from the Red Bay site in Canada (WADDELL 2007,149) is a lengthy and demanding undertaking - meaningless without proper presentation. One Underwater archaeological parks are one of the anode. The sacrificial anode is a metal that cor- tralia, at the Duart Point shipwreck for example of the more complex examples of this kind of most popular methods of in situ presentation rodes more readily - more precisely has a higher (MacLEOD 1995; GREGORY 1999). There is protection of researched archaeological materi- and can be found around the world. Among the- negative potential - usually this is zinc, magnesi- also the recent example from Sicily, where iron al, wood in this case, was implemented at the se we can number all underwater sites or ob- um or aluminium. The two metals create an cannons have been protected in this fashion at Red Bay site in Canada where over 3,000 pie- jects that enjoy legal protection and have been electrochemical cell as a result of which the ano- the Cala Spalmatore site with the purpose of ces of wood were reburied in the seabed developed for visitor access (Figure 8). These de corrodes in favour of the protected cathode, presenting the site as an underwater archaeolo- (WADDELL 2007, 149-151; ORTMANN 2009, may be independent archaeological sites, seve- whereby the degradation of the metal find we gical park (BARTULI et al., 2008). 12-13). Another example of this method of pro- ral archaeological sites in close proximity that wish to protect is significantly retarded tection is in Marstrand harbour in Sweden (MacLEOD 1987; ORTMAN 2009, 17). The sta- REBURIAL OF ARCHAEOLOGICAL where, after several research campaigns, about bilisation of objects in situ also significantly shor- MATERIAL 85% of various archaeological finds of metal, tens the process of conservation if a need arises ceramics, glass, wood and other organic materi- to extract the object from the site (MacLEOD While it cannot in essence be considered a met- al were reburied. Here protection is carried out 1995, 58-59). The shortcomings of this method hod of in situ protection since the archaeological in the frame of a 50-year RAAR (Reburial and are that it is applicable only to metal finds, that finds are researched and their original position Analyses of Archaeological Remains) project the the sacrificial anode has a limited lifetime and altered, this is one of the methods that ensures aim of which is to collect data on the processes needs to be regularly monitored and replaced, the stability of underwater archaeological materi- and intensity of deterioration of various kinds of and that the method is suitable only for smaller al in its natural environment, and we will treat it archaeological materials based on the monito- objects (cannons, anchors) since human and in the context of protecting finds under water. A ring of a broad range of parameters. This kind of financial potential may be a limiting factor when scarcity of financial resources, modest prospects research wishes to comprehend the causative dealing with larger objects. This method of pro- for the restoration and presentation of archaeo- agents of the degradation of archaeological ma- Figure 8. Inside the protected shipwreck Baron Gautsch, tection has been applied for many years in Aus- logical material, and the low historical significan- terials for their more effective future protection Croatia (Photo: N. Starþiü)

Conservation of Underwater Archaeological Finds - MANUAL 106 Pešiü M.: In Situ Protection of Underwater Cultural Heritage 107

together form one large underwater park or ar- There are also a great number of museums that protected zones can be drafted, which may later by preventing bacterial decay of wood in founda- chaeological sites in the frame of nature parks directly link their content to underwater cultural be used as evidence if a site is looted. Monito- tion piles and archaeological sites) which is and reserves. What is common to them is that heritage. Noteworthy are the Mary Rose Muse- ring of sites may also be undertaken using vario- studying the degradation of archaeological they have been researched and documented by um in Portsmouth, Great Britain with its presen- us geophysical methods that monitor the appea- wood, and the research conducted on the wreck experts and that visitor access to these sites, tation of a 16th century warship, the Vasa Muse- rance and changes to the natural surroundings of the James Matthews (RICHARDS 2001; OR- with constant supervision, does not constitute a um in Sweden's Stockholm or the Bodrum Mu- such as erosion of the seabed, and that may TMANN 2009, 28-32). threat of damage or the destruction of the archa- seum of Underwater Archaeology in Turkey. also be beneficial in documenting changes to eological finds that are a constituent part of an archaeological finds and sites. It is, of course, underwater park (DAVIDDE 2002, 84). impossible to protect and monitor the situation at CONCLUSION SITE SUPERVISION all underwater archaeological sites, and this kind Individual cases that may be characterised as of monitoring can only be deployed to a limited Protecting cultural heritage is the primary task of underwater parks have already been cited, inclu- The supervision of underwater archaeological number of key areas. This is why educating the every archaeologist, historian, conservator- ding sites protected by steel cages in Croatian sites is a key step towards preserving local community and interested groups is yet restorer and every other person who comes into waters - but we can also number various underwater cultural heritage. As has been em- another crucial element of the principles of pro- contact with the historical context of finds and shipwrecks, harbour complexes or sunken archi- phasised several times, the greatest threats to tection and monitoring. Presentations, lectures, sites and the underlying premise that should tecture among the archaeological parks. There the preservation of archaeological sites are tho- publications, courses and workshops are only a guide any research effort and the care of archa- are a great number of underwater archaeologi- se coming from human or natural factors. We few of the aspects of education that can bring eological material. The protection of underwater cal parks around the world and as examples we have already described in some detail the legal underwater heritage closer to the broader public cultural heritage in situ is one of the chief guide- can cite the underwater archaeological park off and physical protection of sites, and we shall with the aim of raising awareness and care for lines set out in the UNESCO Convention on the the island of Ustica in Sicily and Baia to the west now briefly touch upon the methods of supervi- its protection. Protection of the Underwater Cultural Heritage of Naples in Italy, the Legare Anchorage and sing them. There are several methods whereby and its Annex, and it should, as such, also be other shipwreck sites within Biscayne National sites can be monitored and protected. We sho- Supervision of the state of underwater archaeo- the first choice when engaging in research. This Park in Florida (SKOWRONEK et al. 1987), the uld above all emphasise the role of experts logical finds in situ is yet another key determi- section has outlined the various methods of le- sunken harbour of Caesarea Maritima in Israel whose regular observation, inspection and col- nant in which experts from the conservation- gal and physical protection of underwater sites (RABAN 1992). In these parks visitors are gui- lections of samples from a site will enable them restoration profession should take an active role. in situ, and the methods of their presentation ded to small finds and features by signs, and the to notice changes on time and properly respond Monitoring the processes of degradation and and supervision. Archaeological research is, finds themselves are accompanied by informati- to them. Sometimes the wider population is not decomposition, changes to the surrounding en- however, often undertaken because of a threat on boards that describe them and provide infor- aware of the location of underwater archaeologi- vironment and to the natural conditions that in- to a site, because of its historical significance or mation concerning their origin and function, and cal heritage, and these places should, therefore, fluence the state of archaeological finds, and simply because of a need to fill in gaps in histori- offer visitors other interesting information related be properly indicated to reduce the negative ef- analyses of all influences on them, help us un- cal knowledge. The result of these research ef- to a given site (DAVIDDE 2002, 85). fects on heritage. Indicating protected zones, derstand and take timely action against the cau- forts is material extracted from an aqueous envi- which can be visibly identified with buoys, is the sative agents. Different causative agents affect ronment, which, at the moment of extraction, is Underwater museums are structures in which basic method of marking off zones in which every kind of archaeological material - metal, in an exceedingly sensitive state and requires underwater cultural heritage is presented in situ activity that could damage cultural property is ceramics, stone, wood - in varying intensity, and the immediate attention of an expert. In the past and that are accessible to the broader public not permitted. These areas can have info sign- each requires a specific approach to monitoring it has often been the case that materials yielded and not only to divers. Currently the largest boards that indicate the reasons for protecting these parameters. Given that these causative by archaeological research, and upon its underwater museum in situ is the Baiheliang the site and the sanctions foreseen for those agents are described elsewhere in the text, we extraction from an underwater environment, was Museum in China - built on dry land prior to the who do not abide by the stipulated restrictions. will only cite a few of the major projects here that often not afforded proper care, conservation, Three Gorges Dam going operational and now Of course it is the competent legal authorities are engaged in studying and monitoring the cau- storage and presentation. It is, therefore, vital lying underwater at a depth of 43 metres. It fea- that play a key role in this system and who need ses of the deterioration of archaeological materi- that, before undertaking any underwater rese- tures inscriptions up to 1,200 years old recor- to conduct periodic monitoring of the site. The al in situ. arch, we secure the prerequisite conditions to ding the movement of the Yangtze River deployment of sonar buoys is also one of the ensure the long-term preservation of underwater (XIURUN 2011, 2). Another major project is an methods that can be used to monitor the site. Besides the already cited and broad - reaching cultural property in a state as similar as possible underwater museum in Alexandria, Egypt that Installed at the site they can warn approaching RAAR project that includes particular study of all to that in which it was found. The in situ method aims to present submerged Egyptian culture, vessels that they are approaching a protected subgroups of materials most frequently found at of protection is certain to see further develop- including small finds and features, the remains zone and send the competent authorities notifi- archaeological sites, also noteworthy are the ment in the future, as will the methods that both of the Alexandrian harbour and the famed cations of unwanted entry to the site. The move- MoSS Project (Monitoring of Shipwreck Sites) preserve and present underwater cultural herita- lighthouse on Pharos (MORCOS 2000, 33, 40- ment of vessels in protected archaeological zo- the aim of which it is to better understand the ge in its original form. 41). nes may also be monitored by satellite, based processes of shipwreck deterioration (PALMA on which maps of the movements of ships in 2005), BACPOLES (Preserving cultural heritage

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