Microscopic Analysis of Japanese and Wax Paper Used for the Preservation of Written Cultural Heritige

Iskra Tsvetanska-Tsekova,Journal Veska of Chemical Lasheva, Technology Ivanka Yankova, and Metallurgy, Irena Peteva, 56, 3, Rumelina 2021, 521-525 Vasileva, Silvia Stanchevа

MICROSCOPIC ANALYSIS OF JAPANESE AND WAX PAPER USED FOR THE PRESERVATION OF WRITTEN CULTURAL HERITIGE

Iskra Tsvetanska-Tsekova1, Veska Lasheva2, Ivanka Yankova1, Irena Peteva1, Rumelina Vasileva1, Silvia Stanchevа1

1 University of Library Studies and Information Technologies Received 15 January 2020 119 Tsarigradsko shoes blvd., 1784 7-Mi Kilometar, Sofia Accepted 20 June 2020 2 University of Chemical Technology and Metallurgy 8 Kliment Ohridski, 1756 Sofia, Bulgaria E-mail: [email protected]

ABSTRACT

The paper is an integral part of our cultural development. Its’ properties are determined by the properties of the fibrous materials of which it is composed by and from the technological regime in its production. The good knowledge of the fibrous materials used, their chemical composition, morphological and anatomical structure in the restoration practice is essential for proper conduction of the recovery procedures. In world restoration practice, Japanese paper is the most often used material for the renovation of paper documents. The examination and microscopic analysis of Japanese paper contributes to its proper use in restoration practice. Keywords: restoration, paper, fibrous materials, Japanese paper.

INTRODUCTION thin sheet. The properties and parameters of the different types of paper depend on the nature of the plant fibres, During the long-term storage, all paper documents on the processing of the fibres, on the composition of undergo a series of physic-chemical changes related to the paper (percentage of fibres, fillers and sizing agents), natural aging. It is impossible to stop the natural aging on the paper-forming technologies and the subsequent process, but it can be slowed down through proper stor- finishing processes. The cellulose fibres in the dry pa- age as well as through limited and careful use. The paper per sheet are connected each other mainly by hydrogen needs to be restored in order to increase the durability bonds. Cellulose fibres have many valuable physical of the stored paper materials and, if possible, to return properties - whiteness (colour), flexibility, elasticity and them to their original form. Conservation and restoration mechanical strength. Under mechanical pressure they operations are carried out in order to protect documents have the ability to change their shape without break- from the negative effects of the external environment and ing. Each cellulose fibre is a cell whose shell consists to strengthen their sustainability. The classic restoration mainly of polysaccharide cellulose. The structure of is reduced to strengthening the paper sheets, using paper the cellulose cell cover is anatomically a complex that and adhesives necessarily close in composition and prop- has a fibrillary structure. Chemically, cellulose is a high erties to the original material of the document. Several molecular mass compound that belongs to the group of types of Japanese paper and mice tape are used. For polysaccharides. The cellulose macromolecule is made the most valuable documents, extremely thin specially up of repetitive structural units - β-d-glucose residues produced silk materials are used. (C6H10O5)n. The number n or the degree of polymeriza- The paper is an elastoplastic, capillary porous sheet tion indicates how many times the structural unit is material consisting mainly of plant fibres, processed in repeated in the cellulose macromolecule and character- a certain way and firmly connected to each other in a izes the molecular chain length and the molecular mass.

521 Journal of Chemical Technology and Metallurgy, 56, 3, 2021

The degree of polymerization, for celluloses of different EXPERIMENTAL origins, is not the same. For example, for wood cellulose Microscopic analysis it is equal to 3,000, for cotton - 12,000, for linen - 36,000. The microscopic analyse of cellulose and paper The connection between the individual structural units materials, is a specific analyse generally used to deter- is made through the oxygen bridge of the first carbon mine the fibre composition of the paper and to study the atom of the single glucoside and the oxygen atom at the structure and size of the source fibres. Small amount fourth carbon atom of the neighbouring nucleus. At the of test fibres (pre-milled mechanically) is placed in a hydrolysis of cellulose, under the action of water and porcelain pounder with a few drops of 1 % NaOH. This heating, in the presence of a catalyst (hydrochloric acid) is followed by rinsing the sample several times with is obtained monosaccharide - glucose. Each structural distilled water on a fine, metal mesh. Three samples of unit of the cellulose molecule has three free hydroxyl fibres have to be placed on a glass slide, distribute well groups. Due to the presence of hydroxyl groups in the with the help of pins, and remove excess water with cellulose molecule, hydrogen bonds appear between the help of filter paper. A drop of Herzberg’s reagent the molecular chains, which ensure the formation of a (Cl - Zn - J) is dropped on each of the samples and sheet of paper with optimal strength [1 - 6]. The hydro- again very carefully the fibres should be distributed. gen bond occurs between the closely spaced hydroxyl Finally, the samples are dried at about 60°C with a lamp. groups of two neighbouring cellulose molecules. During After cooling down to room temperature, each sample the long-term storage of paper, in the form of archival is covered with a thin glass slide, so the fibre samples materials or books, under the action of various physic- to be evenly distributed, free of accumulations and air chemical factors, processes of decomposition of cellu- bubbles. Stained fibre samples were observed under a lose macromolecules to low molecular mass fractions microscope at different magnifications. and most often to hydrocellulose, which has a low degree To determine the type of fibres, the peculiarities of of polymerization, water instability and greatly reduced their structure are studied - shape and size (whether they strength, occur. When the cellulose is oxidized during are flat or cylindrical); presence of tubules - size and storage, the resulting oxy-cellulose, depending on the shape; appearance of their ends; size, type and location degree of oxidation, changes to a powdery mass. Cel- of the pores, as well as the size and shape of the cells. lulose is a highly hygroscopic substance, as a result of The colour and morphological features of the fibres de- which it always contains a certain amount of water. This termine the type of raw material from which the paper property of cellulose fibres is also due to the presence sample is obtained. The Herzberg reagent stains the of hydroxyl groups contained in the molecule. When fibrous materials in the following ways [10]: paper is in an atmosphere that contains water vapour, - Cotton, linen and hemp - pale to intense pink - red; it absorbs it until the occurring of equilibrium in the - Cellulose - blue to violet colour, while the sulphite paper-atmosphere system. The absorption of moisture cellulose is coloured more intensely, and the sulphate - from air by the cellulose macromolecule causes the paler and darker with brownish hues; cellulosic fibres to swell, increasing its volume several - Wood pulp and semi-cellulose - from light yellow times. The papers used in the restoration practice have to yellow-brown colour depending on the yield; a different fibrous composition. Microscopic analysis in - Wool - pale yellow colour; paper production helps to study the structure and size - Artificial fibres - blue colour; of the source fibres, as well as to determine the fibre - Acetate fibres - yellow colour; composition of the used papers. Under different detec- - Synthetic fibres – without any colour. tors, fibre colouring depends primarily on their chemical For the microscopic characterization of the natural composition, as well as on the amount of residual lignin fibres according to their morphological features, the in the fibres itself [7 - 15]. following three characteristics are examined: general The aim of the present work is to make a micro- appearance of the fibres (size and configuration); fibre scopic analysis of the most commonly used in restoration marking (type, size and location of pores, presence of practice Japanese and wax paper with a view to their channel, nature of the ends), accompanying structural appropriate application. elements (core rays, cells and vessels). 522 Iskra Tsvetanska-Tsekova, Veska Lasheva, Ivanka Yankova, Irena Peteva, Rumelina Vasileva, Silvia Stanchevа

Fig. 1. Thin Japanese paper Tengujo.

- Cotton - the fibres are long, tape-shaped without geneous and of different types. Most of the fibres have pointed edges. Most of them are twisted around their torn ends. axis. Their walls are thin, a wide channel passes in the - Wool - the fibres are round, slightly curved, and in centre, and pores and thickenings are missing. some species have a channel. - Flax and hemp - their fibres are long, round in cross - Synthetic and artificial fibres - have a cylindrical section and with a number of nodular thickenings along shape, long, with a smooth surface [10]. the length. Longitudinal stripes and transverse folds and strokes are visible on their surface. They have a narrow RESULTS AND DISCUSSION internal channel. Different types of Japanese paper are used in the res- - Coniferous (softwood) cellulose – 90 % of the toration practise. Of interest is the microscopic analysis fibres are long ribbon-shaped cells – tracheides. They of the most commonly used types of Japanese paper. have characteristic pores, which are seen as two different Japanese paper is highly valued by the experts around shapes, depending on the type; the world as a high-quality material for repairing damage Pine cellulose - is characterized by large “window” of paper-based objects. Several types of Japanese paper pores, located in groups. samples and a sample of wax paper were studied to de- Spruce pulp - with small and rounded pores. termine the fibre composition by the microscopic method. - Deciduous (hardwood) cellulose - relatively short, Sample No 1 is made of thin Japanese Tengujo paper thick-walled cells with pointed edges. with a basic weight of 10 g m-2. During the microscopic Their pores are small, narrow and located at an analysis it was found out that the result of the three angle to the axis of the fibre. Each of the species has its visual fields, shown on Fig. 1, represents the fibres in uncial vessel: intensive pink - red colour of fibres. The results indicate Beech pulp - the vessels are thick and obliquely the presence of all-cotton fibres, which are long, without cut. Most have fully open holes at both ends. They are pointed edges and tape-shaped structure with no thick- covered unevenly with round and elongated pores. enings and pores, and their walls are thin, with a wide Poplar pulp - their vessels have open ends, and the channel in the centre. fibres are thin-walled, spindle-shaped, with very pointed Sample No 2 is Japanese Senkwa paper with a edges and small pores. weight of 41 g m-2 and the results from the microscopic Birch cellulose - the vessels are covered with nu- analysis (Fig. 2) revealed predominant presence of fibres merous pores, significantly smaller than those of other of bleached coniferous spruce pulp. Its fibres have small tree species. and rounded pores. The long, ribbon-like and without - Straw pulp - contains a wide variety of cells, the pointed edges, without pores and thickened fibres indi- main ones being long, thin, tape-shaped with pointed cate the presence of cotton fibres. ends. There are also annular and thin, spiral cells that Sample No 3 is of Japanese Minota paper with a have small pores on their walls. grammage of 26 g m-2 and its microscopic analysis (Fig. 3) - Wood pulp - according to the manner and degree shows the presence of bleached coniferous pulp fibres of treatment of the raw material, the fibres are hetero- from spruce wood - its fibres have small and rounded

523 Journal of Chemical Technology and Metallurgy, 56, 3, 2021

Fig. 2. Japanese paper Senkwa.

Fig. 3. Japanese Minota paper.

Fig. 4. Japanese Zubiki paper.

Fig. 5. Mike paper. pores. The long, ribbon-like and without pointed edges and numerous thickenings along the length of the fibres and without pores and thickened fibres indicate the pres- indicates the presence of small amounts of flax. ence of cotton fibres. Sample No 5 is of Mike paper with basic weight Sample No 4 is of Japanese Zubiki paper with a of 17 g m-2, the microscopic analysis of which (Fig. 5) grammage of 14 g m-2, whose microscopic analysis shows the presence of bleached cellulose fibres, prov- (Fig. 4) showed three different types of fibres: fibres ing the presence of silk, as well as the presence of long, with small and rounded pores (evidence of bleached with cross sectional and numerous thickenings along the coniferous pulp from spruce wood), long and ribbon- length fibres, which is evidence of low flax fibre content. free fibres without pores and pointed edges (evidence of Sample No 6 is of wax paper with a basic weight of cotton fibres), and the presence of long, cross-sectional 50 g m-2 (Fig. 6). This type of paper is used for pressing

524 Iskra Tsvetanska-Tsekova, Veska Lasheva, Ivanka Yankova, Irena Peteva, Rumelina Vasileva, Silvia Stanchevа

Fig. 6. Wax paper. the paper samples and prevents them from sticking to restoration of paper, http://www.electronic-library. each other. Its composition is dominated by bleached org/books/Book_0073.html coniferous pulp of spruce and pine wood, as well as 5. D.A. Todorova, S.P. Bencheva, Investigation on the the typical thick, obliquely cut vascular cells, typical of influence of chemical additives over the behavior broadleaf pulp fibres from beech wood. of paper furnish from recycled newspaper fiber material, Bulg. Chem. Comm., 47, special issue A, CONCLUSIONS 2015, 45-50. From the results of the microscopic analyses of the 6. S.A. Dobrusina, E.S. Chernina, Preservation of docu- different types of Japanese paper and the wax paper ments: science and practice, St. Petersburg, 2013, used in the restoration practice, it was established that (in Russian). by their nature the Japanese paper used for restoration 7. S.A. Dobrusina, Stabilization of documents, purposes is made mainly of thin and long fibers. Its Moscow, 2014, (in Russian). finely fibrillated fibers, combined with its sheet-forming 8. E. Smirnova, Improving the stability of paper to ag- process, make it possible to obtain very transparent and ing by the formation of its composition, Ph.D. thesis, mechanically strong paper, which is extremely important St. Petersburg, 2014, (in Russian). for the material used in the restoration. Its high porosity 9. N. Yavorov, I. Valchev, G. Radeva, D. Todorova, is also important, which allows the close contact with Kinetic investigation of dilute acid hydrolysis of the restored surface. The use of a particular type of hardwood pulp for microcrystalline cellulose pro- Japanese paper is consistent with each paper document duction. Carbohydrate Research, 488, 2020, 107910, undergoing restoration. DOI 10.1016/j.carres.2020.107910 10. N. Ivanova, S. Bencheva, D. Todorova, A Guide Acknowledgements to Exercises in the Chemistry, Technology and The authors acknowledge the support of the Science Properties of Paper, Sofia, UCTM, 2009, (in Fund of the University of Library Studies and Informa- Bulgarian). tion Technologies (project № КП-06-Н40/1). 11. E.M. Lotsmanova, E.S. Bistrova, Atlas of damage to paper, block, binding of library and archival materi- REFERENCES als, St. Petersburg, 2011, (in Russian). 12. R. Tsenkova, V. Lasheva, Restoration of works of 1. V.P. Egorov, A.V. Slinkov, Preservation, restoration art by the method of classical restoration, 4, 61-65, and preservation of documents, Moscow, 2014, (in ISSN0861-847Х, 2018, ceeol.com, (in Bulgarian). Russian). 13. http://elar.rsvpu.ru/bitstream/123456789/12314/1/ 2. D.M. Flate, Properties of paper, Moscow, 1983, (in RSVPU_2016_034.pdf Russian). 14. http://naar.ru/articles/restavratsiya-materialyi/ 3. R. Draganova, S. Nenkova, Chemistry and structure 15. N.A, Khramtsovskaya, Destruction and restoration of plant tissues, UCTM, 2002, (in Bulgarian). of documents, Basics of paperwork, 12, 2005, 19, 4. G. Saikova, Basic methods for conservation and (in Russian).

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