Northeast Historical Archaeology
Volume 26 Article 5
1997 Cellulose Nitrate Plastic (Celluloid) in Archaeological Assemblages: Identification and Care Megan E. Springate
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Recommended Citation Springate, Megan E. (1997) "Cellulose Nitrate Plastic (Celluloid) in Archaeological Assemblages: Identification and Care," Northeast Historical Archaeology: Vol. 26 26, Article 5. https://doi.org/10.22191/neha/vol26/iss1/5 Available at: http://orb.binghamton.edu/neha/vol26/iss1/5
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Cover Page Footnote Several people have been extremely helpful in preparing this paper. My thanks to Heather Henderson, for first sparking my interest and for supplying refernces, and to both Mary Ann Elliott nda Gayle McIntyre of the Collections Conservation and Management program at Sir Sandford Fleming College, Peterborough, Ontario for their support, editorial assistance, and the use of their personal libraries. I would also like to express my thanks to the editorial staff of orN theast Historical Archaeology, including Mary C. Beaudry, Cassandra Michaud, and Ann-Eliza H. Lewis who were all very helpful in the preparation of this paper. My gratitude also to the two anonymous reviewers who provided extremely helpful feedback. All errors are my own. Last but not least, special thanks to my family, especially Marcia.
This article is available in Northeast Historical Archaeology: http://orb.binghamton.edu/neha/vol26/iss1/5 Nortlzcnst Historical Arc/wcologyNol. 26, 1997 63
Research Notes
Cellulose Nitrate Plastic (Celluloid) in Archaeological Assemblages: Identification and Care
Megan E. Springate
Invented in the mid-19th century, cellulose nitrate is commonly regarded as the earliest synthetic polymer or plastic. As increasing numbers of historical sites dating from the mid-1800s are excavated, cellu lose nitrate objects are more frequently found in archaeological assemblages. The inherent instability of cellu lose nitrate makes proper handling, storage, and display conditions vital to the longevity of recovered objects. In this paper, the composition, manufacture, and means of identifying cellulose nitrate arc summarized. The processes of degradation and means of slowing those processes are elaborated, as well. Invente au milieu du XIX' siecle, le nitrate de cellulose est considere comme le plus ancien polymere synthetique, ou plastique. A mesure qu 'on fouille des sites historiques datant du milieu des annees 1800, on trouve de plus en plus frequemment des objets en nitrate de cellulose dans des assemblages archeologiques. A cause de l'instabilite inherente du nitrate de cellulose, de bonnes conditions de manipula- Introduction which is generally accepted to be the first plastic, were displayed at the 1862 Interna The earliest synthetic plastics, including tional Exhibition. Celluloid, a less flammable Celluloid and Bakelite, have been in existence cellulose nitrate plastic than Parkesine, made for almost a century and a half. As a result, with a camphor plasticizer, was first registered they are found with increasing frequency in in the United States by Hyatt in 1872; in 1877, archaeological assemblages. Unfortunately, the British Xylonite company was established there has not been a corresponding increase in to manufacture Celluloid in Britain (Katz 1986: the archaeological literature regarding these 19; Morgan 1991: 21; Mossman 1993: 26; substances-their composition, manufacture, Williams 1997a). means of identification, processes of degrada Until about 1920, cellulose nitrate was the tion, and how best to store them to prevent only commonly available colorless, trans deterioration. This paper will focus on the ear parent plastic (Williams 1997a); it was also liest synthetic plastic, cellulose nitrate. easily dyed, and the range of colors possible Also known as nitrocellulose, trade names was virtually unlimited (Morgan 1991: 21). In for this plastic include Celluloid, Collodion, fact, cellulose nitrate has been used as a con Pyralin, Pyroxylin, Xylonite, HMG, Parkesine, vincing imitation of ivory, tortoiseshell, bone, Fabrikoid, Viscoloid, Ivoride and French Ivory horn, mother-of-pearl, coral, and leather. (Clydesdale 1982; Katz 1986: 19; Morgan 1991: Objects made from cellulose nitrate included: 21; Williams 1997a). It can be found in many combs, dresser ware, boxes, toys, cutlery han forms, depending on the amount of nitrogen dles, jewelry, drafting set-squares, drawing present, in items ranging from gun powders to templates, spectacle frames, buttons, and toilet photographic films to fabrics to the focus of seats (FIG. 1) (Katz 1986: 19; Williams 1997a). this paper, plastic objects. The versatility, low cost, and world-wide Used in explosives and photographic films availability of cellulose nitrate made it one of from the 1840s, cellulose nitrate was first made the most widely used plastics for almost 100 into a plastic in 1856 by Birmingham inventor years. Still in production, cellulose nitrate has Alexander Parkes using a solvent casting been surpassed in popularity by other more process. Samples of the resulting Parkesine, stable plastics (Fenn 1994: 46; Williams 1997a). 64 Cellulose Nitrate Plastic ldentifiaction and Care/Springate
Figure 1. Celluloid handled straight razors .Deterioration is causing darkening. and crazing (not visible). The bottom razor has a dark-brown handle. Note the whitish blooms, md1catmg detenorahon. (From the author's collection)
The Chemistry of Cellulose Nitrate nitrated cellulose, known as guncotton, is used as both an explosive and a propellant (Gille Cellulose nitrate does not have a fixed spie et a! 1989: 1096). The reactive sites of cel chemical formula; rather, it is "a polynitrate lulose nitrate are the nitrate groups (Williams ester of the natural polysaccharide, cellulose" 1997a). (Selwitz 1988: 1). This semi-synthetic or chemi During the manufacture of cellulose nitrate cally modified natural polymer is created plastic, plasticizers such as camphor and when cellulose in the form of cotton or wood castor oil are added. These plasticisers are rel pulp is reacted with nitric acid (Clydesdale atively involatile substances which separate 1982; Morgan 1991: 21). During this reaction, the molecules of individual polymers. This some hydroxyl (-OH) groups of each glucose weakens the inter-molecular bonds and allows unit in the cellulose are replaced by nitrate the long molecular chains of the plastic to (-ON0 ) 2 groups. The number and position of move relative to one another. Cellulose nitrate these groups varies, which is why there is no on its own is a hard, brittle plastic at ordinary definitive chemical formula. temperatures; with a plasticizer, it becomes The amount of nitration dictates both the more resilient and easier to work (The Conser form and the stability of cellulose nitrate: plas vation Unit 1987: 43-44). tics and lacquers contain 10.5 to 11.5 percent nitrogen; lacquers, films, and sheets contain Manufacturing Processes between 11.5 and 12.3 percent nitrogen; while explosives and gun powders contain 12.4 to As cellulose nitrate plastic could not easily 13.5 percent nitrogen (Williams 1997a). Fully be molded into objects, thin sheets were sliced Northeast Historical Arclwco/ogy/Vol. 26, 1997 65 from blocks of material. Parallel lines or Identification of Cellulose Nitrate scratches caused by the cutting blade can often be seen on the surfaces of cellulose nitrate When dealing with collections of plastics, objects, especially when examining unfinished it is crucial that they be properly identified so surfaces with a lOX magnifying lens (Morgan that the appropriate cleaning, stabilization, 1991: 21; Williamson 1992: 4). Objects were and storage measures may be observed. then formed from these thin sheets by thermo Infrared spectroscopy is by far the most accu forming or blow molding. rate means to identify cellulose nitrate; how In the thermoforming process, the thin ever, this method may not always be acces sheets of cellulose nitrate were heated using sible. Following are some other observations an oven, hot water or hot oil bath, or the use of and tests to aid in the identification of cellu infra-red or dielectric heating. These plastic lose nitrate. sheets were then shaped by bending or forcing them into a mold using a vacuum, air pres Visual Appearance sure, or a matched tool in a process similar to While cellulose nitrate was the earliest press molding (Morgan 1991: 47). clear plastic, later polymers such as cellulose Blow molding involved the clamping acetate, plasticized poly (vinyl chloridP.), poly together of two warmed sheets of cellulose (methyl methacrylate), polystyrene and poly nitrate between mold faces. Air was then ester are all now commonly used to produce blown between the sheets, forcing them into clear materials. Neither is the presence of a the mold. In some cases, plaster was used to high gloss sufficient to distinguish cellulose fill the resulting hollow to give the objects nitrate. Other plastics, including poly (methyl more weight (Morgan 1991: 47). Ping pong methacrylate), other cellulosics, polystyrene balls were manufactured for almost one hun and polished casein may also have glossy fin dred years using this blow molding process ishes (Morgan 1991: 36). (Williamson 1992: 5). The most convincing imitations of ivory are made of cellulose nitrate. While the plain color of ivory can be imitated using many other plastics, only cellu!ose nitrate can be manufactured to have a grain, color, and weight almost identical to ivory. Imitation tor toiseshell is likely to be either casein or cellu lose nitrate, which has a greater brilliance and clarity than both casein and natural tortoise shell (FIG. 2) (Morgan 1991: 36; Williamson 1992: 4). Under low power magnification (such as that provided by a lOX hand-held Ioupe), one may see the distinctive weathering pattern of celluloid nitrate; consisting of a series of con choidal fractures forming a checked pattern.
Odor When gently warmed, by either rubbing or washing in warm water, a slight camphor smell may be released (Morgan 1991: 37). The lack of a camphor smell does not preclude the Figure 2. Celloid was often used to make con test sample from being cellulose nitrate, as vincing tortoiseshell imitations for items such as many other plasticizers were used during hairhair combs. (Image from Grafton 1994:2) manufacture. 66 Cellulose Nitrate Plastic ldentifiaction and Care/Springate
Physical Tests erating degradation. Thus, it is crucial to rec ognize the early stages of deterioration, so that Because of similarities to many other plas the process may be slowed (Morgan 1992: 1). tics, neither the specific gravity (1.3 to 1.4) nor The reactive sites of cellulose nitrate are the placement on the Barco! hardness scale the nitrate groups themselves. During degra (around 70) are sufficient to identify cellulose dation, the liberated oxides of nitrogen, nitrate (Morgan 1991: 39-40). including nitrous oxide and nitric oxide, may react with atmospheric moisture to form acids Chemical Tests such as nitric acid. It is the presence of the Although testing for the presence of resulting acidic conditions which further accel nitrogen is possible, this is not sufficient to erates degradation, eventually causing the identify cellulose nitrate as there are a number main polymer chain to break (Morgan 1991: of other polymers which also contain nitrogen. 21-22; Williams 1997a). These include nitrile rubber, polyurethane, Five stages of deterioration have been casein, melamine-formaldehyde, nylon, and described for cellulose nitrate film. The same urea-formaldehyde (Saunders 1966: 22). progression can be expected for cellulose The pH of the plastic fumes may be deter nitrate objects, albeit at a slower rate, due to mined by heating a small sample in a test tube the lower concentration of nitrogen. These (a fine emery paper may be used to remove a stages include progressive yellowing (to dark sample from an unobtrusive area). A piece of brown), checking and crizzling, the formation moist litmus paper is then held in the mouth of bubbles or foam on the surface, and embrit of the test tube. The presence of acidic fumes tlement and shrinkage (FIG. 3). All of these (i.e., a pH between 1 and 4) suggests that the stages are accompanied by the foul odor of plastic may be cellulose nitrate. Note, how nitrogen oxide gases (Williams 1997a). A misty ever, that cellulose acetate, polyurethane, haze-type bloom with an acidic "taste" is one polyester, and poly (vinyl chloride) also give of the earliest signs of cellulose nitrate deterio off acidic fumes upon heating (Morgan 1991: ration (Williamson 1992: 4). These visual 37; Williamson 1992: 7-8). changes are accompanied by an associated A small sample of the plastic (again, a fine decrease in auto-ignition temperature, which emery paper may be used, and this method is is the lowest temperature at which an object preferred over testing the object directly) may will self-ignite without a direct heat source. be heat tested, using extreme caution as cellu Undegraded cellulose nitrate auto-ignites at lose nitrate is extremely flammable. Positive about 325°F (150°C); in the last stages of dete observations for this test include the fol rioration, when all that is left is a powdery or lowing: the material burns very quickly and foamy mass, the self-ignition temperature of continues to burn after it is removed from the cellulose nitrate can be as low as l25°F flame; the plastic burns with a yellow color; (50°C)-a temperature easily reached near and a camphor odor may be noticed (Saunders light bulbs, heat sources, and in unventilated 1966·.18). storage areas in summer months (Williams Although the above mentioned tests and 1997a). Deteriorated cellulose nitrate objects observations may ail be used to suggest the are extremely fragile, and may even break presence of cellulose nitrate, the dipheny under their own weight. lamine spot test is the best chemical method to If allowed to build up, the products of cel identify this polymer (Williams 1997a). A full lulose nitrate deterioration can result in what description of the diphenylamine spot test can is known as an antagonistic synergistic effect, be found in Appendix A. also known as "bad neighbors." In these situa tions, the close proximity of one material (in Deterioration this case, cellulose nitrate) induces or acceler The progression of cellulose nitrate deteri ates the degradation of another, such as the oration is typical of most polymers. Specifi corrosion of metals, and the embrittlement and cally, a long period of deterioration where little discoloration of organics (Morgan 1991: 15; change is visible is followed by rapidly accel- Williams 1997a). The following are brief Northeast Historical Archacolos:yNol. 26, 1997 67
CARVERS.
N<_l. UlH!. ~ra~lll~d. eP.H11loid hllndle CtU'VC!rll. with diffic:1l~ dietln~i.shed hill tvnn;, wt.,,·h Jt. WJil "'J!la~t. Jlla
Figure 3. Celloid-handeled knives from the 1897 Sears and Roebuck catalogue (Israel1993:108) descriptions of conditions leading to the chem items, such as photographic films, the nitrogen ica:! alteration and deterioration of cellulose oxide gases quickly diffuse out of the object nitrate. and may be vented away. In the case of thicker object such as cutlery handles, however, the diffusion of these gases out of the object is Inherent Vice slower. Cellulose nitrate deterioration is auto This category includes effects of manufac catalytic. That is, the acids created by the turing which play a role in deterioration. Cel degradation process encourage further deteri lulose nitrate is, itself, an unstable polymer. oration. As a result, in thicker objects, where While careful preparation of cellulose nitrate the nitrogen oxide gases and acids are trapped and careful fabrication of objects can reduce within the object longer, there is more oppor the rate of decay, there is currently no effective tunity for them to catalyze even further deteri means of completely stopping the deteriora ora.tion (Williams 1997a). This process of auto tion process (Williams 1997a). catalyzation results -in visible internal cracks Cellulose nitrate manufactured with a high which spread rapidly throughout the object nitrogen content (usually over 13 percent), (Williamson 1992: 5). The heat created by this which is primarily used for explosives or gun exothermic reaction may cause the object to powders, is very unstable, and can easily spontaneously ignite (Williams 1997a). explode if subjected to heat, friction, or shock. Plasticizers, such as camphor, are not nec Objects made of cellulose nitrate plastic (usu essarily tightly bound within the structure of ally having a nitrogen content of 12 percent or less) are not this explosive; they are, however, the plastic. Thus, over time, they are lost extremely flammable (Williams 1997a). through sublimation, resulting in a loss of The percentage of nitrogen present is not lustre, distortion, embrittlement, and an object the sole cause of deterioration; the form of the which is easily soiled (Morgan 1991: 23; object also plays a role. In the case of thin Williamson 1992: 4). 68 Cellulose Nitrate Plastic Identifiaction and Care/Springate
Environmental Conditions lulose nitrate objects should be isolated and stored in a ventilated and fire-proof area Light, heat, and a high relative humidity (Williams 1997a). encourage deterioration of cellulose nitrate. The degradation process is also accelerated by the presence of acidity, alkalinity, or certain Ventilation metals which may be found as impurities in Good ventilation is crucial to lengthening the plastic itself, or as component parts of an the life of cellulose nitrate, since it removes object (Morgan 1991: 21). nitrogen oxide gases from the vicinity of the Ultraviolet light is particularly harmful as objects. Objects in storage should be loosely it tends to break the cellulose polymer back packed to encourage air circulation, and there bone, weakening the plastic. As a result, should be at least one complete air change per objects discolor and yellow, weaken, embrittle, day. The vented air contains harmful gases craze, crack, or break. Once this deterioration and should not be allowed to circulate to other process has begun, it will continue even in the areas of a collection (Morgan 1991: 22; dark (Williams 1997a). Heat also encourages Williams 1997a). Note that oxygen-free storage the deterioration and weakening of cellulose of cellulose nitrate materials is not recom nitrate. mended-containment of these items in an All moisture, including that present as a oxygen-free enclosure with no ventilation will result of a high relative humidity, is detri accelerate deterioration (Williams 1997b). mental to cellulose nitrate products, because it readily combines with nitrogen gases pro Light duced during cellulose nitrate deterioration, To prevent light damage, cellulose nitrate forming harmful nitric acid (Williams 1997a). should not be exposed to sunlight or illumi The presence of this acid encourages further nated strongly. All ultraviolet rays, particu deterioration. larly those from fluorescent lighting and the sun, should be screened out with ultraviolet Biological Degradation filters. Cellulose nitrate should be considered Although based on cellulose, nitrocellulose particularly vulnerable to light and exposed to is not generally subject to biological attack no more than 50 lux (Morgan 1991: 16; (Morgan 1991: 23). Williams 1997a).
Handling Relative Humidity While undeteriorated cellulose nitrate is Because atmospheric moisture is a major quite resilient and robust, in a degraded condi factor in deterioration, cellulose nitrate objects tion it must be handled with caution. Vibra should be kept in an environment with a rela tions, such as those encountered during trans tive humidity below 40 percent (Morgan 1991: portation, and direct physical shock (i.e., drop 10, 22). ping an object) can result in the disintegration of unstable cellulose nitrate. Temperature Arresting and Preventing Deterioration Cellulose nitrate should be stored below 68°F (20°C), with a temperature of 50°F (10°C) Once begun, the deterioration of cellulose being preferable. The relatively low auto-igni nitrate cannot be stopped. It is, however, pos tion point of degraded cellulose nitrate means sible to slow down the reactions of degrading that temperatures should never be permitted materials, and to protect undegraded objects. to rise above 85°F or 30°C (Morgan 1991: 22; Ventilation and the exclusion of light are the Williams 1997a). When moving objects to and most important factors in maintaining stability from cold storage, they must slowly be accli (Morgan 1991: 22). Also, due to the detri matized to the new environment so that con mental effects that the products of deteriora densation of water vapor and thermal stresses tion can have on other objects, degrading eel- are avoided (Williams 1997a). Northeast Historical Archaeology/Val. 26, 1997 69
If a refrigerator is to be used to keep cellu When storing objects made of cellulose lose nitrate objects cool, be certain that a high nitrate, it is advisable to prevent contact relative humidity is not produced during the between the plastic and any metals, especially refrigeration cycle, as is the case in some frost copper; this may be accomplished by using an free models (Williams 1997a). Note that if the inert barrier film such as Mylar. If possible, the humidity and ventilation of the storage area disassembly of any thick sections is also rec cannot be controlled, then the storage of cellu ommended, to allow for the greater rate of lose nitrate below room temperature is not rec release of deterioration products (Morgan ommended (Morgan 1991: 22). 1991: 22).
Other Considerations Washing Cellulose nitrate must not be allowed to Cellulose nitrate objects should be cleaned come into contact with buffered papers or periodically to remove surface dirt accumu other alkaline materials. This includes acid lated during handling and storage, as well as free papers which contain calcium carbonate to remove any degradation products that may (i.e., Woolfitt's "super acid free" paper). While have formed. Other than gentle surface alkalinity encourages the degradation of cellu dusting with a soft brush, cleaning should lose nitrate, deliquescent nitrate salts may also only be done by a conservator familiar with form on the object (Dignard 1994: 3). the plastic. Polishes, waxes, and other film-forming materials are often found on the surface of cellulose nitrate objects. These coatings Monitoring encourage degradation by trapping deteriora Regular monitoring of cellulose nitrate col tion products, such as nitric acid, against the lections for early signs of deterioration is the object. A conservator familiar with cellulose best means of preventing damage to large por nitrate should be consulted regarding the tions of the collection. In some cases, preven proper removal of these coatings. tive treatments or storage decisions may be If repairs are required, avoid solvent-based carried out in order to slow down the rate of adhesives. The solvents will cause deteriora decomposition, while in other instances tion of the cellulose nitrate, and the joins are greatly deteriorated objects may have to be likely to remain weak and liable to fail. In gen isolated from the collection in order to prevent eral, it is best to avoid repairs unless either combustion or the catalyzation of deteri absolutely necessary, and a conservator oration in other objects (Morgan 1991: 10; familiar with cellulose nitrate should be con Williams 1997a). Indicator cards, such as those sulted. Solvents should also not be employed manufactured by 3M, are available that mea to "de-water" these items during cleaning, as sure atmospheric pollutants and compounds they may dissolve the plasticizers, causing off-gassed from materials during deteriora damage. When using any adhesives, the proper tion. These may be a helpful addition to a safety procedures should be observed; consult monitoring program. the appropriate Material Data Safety Sheet, available from the manufacturer or supplier. Note that nail polish and Acryloid B-72, Conclusion often used to label artifacts, also contain sol Objects made of cellulose nitrate, as well as vents which are damaging to cellulose nitrate. other early plastics, are increasingly making A first indication of damage is the appearance their way into archaeological assemblages and of crazing under the label. Water-based mate collections. When one considers the immense rials, such as clear acrylics, are better choices impact of plastics on society, the value of these for labeling cellulose nitrate. Use as little water early examples becomes apparent. While we as possible in the mixture, since water also may think of plastics as permanent substances causes deterioration (Derrick and Stulik 1993: that never break down in landfills, early plas 180). tics such as Celluloid and other varieties of eel- 70 Cellulose Nitrate Plastic ldentifiaction and Care/Springate
lulose nitrate are inherently unstable and are Plastics. In Saving the Twentieth Century: very susceptible to their surroundings. The Conservation of Modern Materials, ed. by The deterioration of these early plastics is David W. Grattan. Proceedings of a Con ference, Symposium 1991, 395-409. Cana inevitable; however, precautions in their care dian Conservation Institute, Ottawa. and handling can slow this process consider ably. The best preventive measures include a Derrick, Michele, and Dusan Stulik regular monitoring and cleaning schedule to 1993 Deterioration of Cellulose Nitrate Sculp isolate any badly deteriorated objects, and tures Made by Gabo and Pevsner. In storage/ display in a low relative humidity Saving the Twentieth Century: The Conserva (less than 40 percent), low light (no UV, and tion of Modern Materials, ed. by David W. no more than 50 lux), and low temperature Grattan. Proceedings of a Conference, Symposium 1991, 169-182. Canadian Con (between 50°F-68°F, or 10°C-20°C) environ servation Institute, Ottawa. ment with lots of ventilation (at least one full air change per day). Dignard, Carole 1994 Report on Work with Plastics with David Pet Acknowledgments tersson, Malcolm Bilz, and Scott Williams. Report prepared for the Canadian Conser Several people have been extremely helpful in vation Institute, May 31, 1994, Ottawa. preparing this paper. My thanks to Heather Copies available from the Canadian Con Henderson, for first sparking my interest and servation Institute. for supplying references, and to both Mary Fenn,Julia Ann Elliott and Gayle Mcintyre of the Collec 1994 Celluloid Crisis. IIC-CG 20th Annual Con tions Conservation and Management program ference (Toronto) Abstracts. IIC-CG (Interna at Sir Sandford Fleming College, Peterbor tional Institute for Conservation-Canadian ough, Ontario for their support, editorial assis Group), Toronto. tance, and the use of their personal libraries. I would also like to express my thanks to the Gillespie, Ronald J., David A Humphreys, N. Colin editorial staff of Northeast Historical Archae Baird, and Edward A. Robinson ology, including Mary C. Beaudry, Cassandra 1989 Chemistry. 2nd ed. Allyn and Bacon Inc., Needham Heights, MA Michaud, and Ann-Eliza H. Lewis who were all very helpful in the preparation of this Katz, Sylvia paper. My gratitude also to the two anony 1986 Early Plastics. Shire Album 168. Shire Pub mous reviewers who provided extremely lications Ltd., Cromwell House, UK. helpful feedback. All errors are my own. Last but not least, special thanks to my family, Morgan, John especially Marcia. 1991 Conservation of Plastics: An Introduction to their History, Manufacture, Deterioration, References Identification, and Care. The Plastics Histor ical Society and The Conservation Unit, Clydesdale, A Museums & Galleries Commission, 1982 Chemicals in Conservation: A Guide to Pos London. sible Hazards and Safe Use. Conservation 1992 Plastics Historical Society: Notes on Bureau, Scottish Development Agency, Degradation of Plastics. Plastics Historical Scottish Society for Conservation and Society Conservation Unit Workshop Notes, Restoration, Edinburgh. May 11, 1992. Plastics Historical Society, London. Conservation Unit, The 1987 Science For Conservators. Volume 3: Adhe Mossman, Susan sives and Coatings. Conservation Science 1993 Plastics in the Science Museum, London: A Teaching Series. The Conservation Unit, Curator's View. In Saving the Twentieth Museums and Galleries Commission, Century: The Conservation of Modern Mate London. rials, ed. by David W. Grattan. Proceed ings of a Conference, Symposium 1991, Coxon, Helen C. 25-35. Canadian Conservation Institute, 1993 Practical Pitfalls in the Identification of Ottawa. Northeast Historical Archaeology/Val. 26, 1997 71
Selwitz, Charles The Procedure 1988 Cellulose Nitrate in Conservation. Research in Conseroation 2. The Getty Conservation From an unobtrusive area of the object, Institute. take a tiny chip or scraping or use fine emery paper. The total sample need not be larger Saunders, Keith J. than a pin head, as the test is extremely sensi 1966 The Identification of Plastics and Rubbers. tive. Place the sample on a glass surface or on Chapman and Hall, Ltd., London. a white glazed porcelain spot plate. Using a Williams, R. Scott pipette or eye dropper, place a single drop of 1994 The Diphenylamine Spot Test for Cellu the reagent onto the sample. If the sample lose Nitrate in Museum Objects. CCI Note quickly stains a blue-violet color whieh dif #17 /2. Canadian Conservation Institute, fuses into the test drop, the presence of cellu Ottawa. lose nitrate is indicated. If there is no color 1997a Display and Storage of Museum Objects change, or other colors such as orange, yellow, Containing Cellulose Nitrate. CCI Note brown, or green appear, the absence of cellu #15/3. Canadian Conservation Institute, lose nitrate is indicated. Ottawa. 1997b Care of Objects Made from Rubber and Plastic. CCI Note #15/1. Canadian Conser Cautions vation Institute, Ottawa. For reliable results, the object to be tested Williamson, Colin must be clean. Any dust or oozing plasticizer 1992 Notes on Identification of Plastics. Plastics on the surface of an object, or embedded in Historical Society Conseroation Unit Work surface cracks, may give a false positive for the shop Notes, May 11, 1992. Plastics Historical presence of cellulose nitrate. Cross-contamina Society, London. tion is also a concern due to the highly sensi tive nature of the test-a pipette which has accidentally come into contact with a cellulose Appendix: The Diphenylamine Spot nitrate object prior to testing can also give a Test For Cellulose Nitrate (from false positive if used on a non-cellulose nitrate Williams 1994) object. The diphenylamine test should never be used directly on the surface of an object, due· to the potential of marking or discol The Reagent oration (Coxon 1993: 404). False results are Slowly add 90 ml of concentrated sul possible when materials, such as pigments phuric acid to 10 rnl of water while constantly containing chromates (yellow, orange, or stirring. Add this 90 percent sulphuric acid, in green), or coatings containing ester gums, small portions and while stirring constantly, to copal, and other natural resins, are present 0.5 g of diphenylamine. Use extreme caution; (Williams 1994: 2). this reaction is very exothermic. Have lots of water, particularly running water, nearby to Notes flood any spills. Other published diphenylamine spot test This solution is very corrosive. It may be "recipes" call for varying proportions of com stored for several years and is effective even ponents in creating the reagent (see, for after it becomes slightly blue or brown. Store example, Coxon 1993, who calls for a 5.0 per this solution in glass bottles labeled "0.5 per cent solution). Tests conducted by the Cana cent Diphenylamine in 90 percent Sulphuric dian Conservation Institute using the 0.5 per Acid; Corrosive." Be certain to use stoppers cent solution described above indicate that it is which are resistant to 90 percent sulphuric effective; 30 samples of objects, coatings, and acid (i.e., not paper, cork, rubber, or metal adhesives were selected. Each sample was foil). tested using the diphenylamine test, as well as 72 Cellulose Nitrate Plastic Identifoiction and Care/Springate
tested using the diphenylamine test, as well as Megan Springate has a Master's degree in Anthro pology, focuing on Historical Archaeology, from examined using infra-red spectroscopy (IR}. Trent University, Ontario, and has completed a two All samples that were shown through IR to year college diploma in Collections Conservation contain cellulose nitrate gave positive spot test and Management through Sir Sandford Fleming College, Ontario. Her research interests include the results; all those shown not to contain cellulose introduction, spread, and "meaning" of mass-pro nitrate tested negative. There were no prob duced coffin hardware, as well as the use of space in and around buildings. lems with contamination (Williams 1994: 2). Materials required to conduct the dipheny Megan E. Springate lamine test are available from standard chem 191 Thousand Oaks Drive ical suppliers. Atlantic Highlands, NJ 07716 mspringa [email protected]