Tátrai Vilmos szerk.: A Szépművészeti Múzeum közleményei 94. (Budapest, 2001)
DÁGI, MARIANNA - SIPOS, ENIKŐ: Report on the Conservation of Coptic Textiles in the Department of Greek and Roman Antiquities (1999-2000)
NOTE ON THE CONSERVATION OF COPTIC TEXTILES Archaeological textiles form a very special group among woven fabrics. In most cases, they survive in environments where they are not exposed to constant climatic change. The deterioration of textiles is a consequence of the interplay of physical, chemical and biological environmental factors and the objects themselves. A state of equilibrium comes into being between the buried object and its environment. If this equilibrium is upset, as it often is in the course of excavation, sudden contact with the air, and temperature changes, will cause the object to fall to dust before the eyes of the archaeologist. Alongside everyday fraying and abrasion, the presence or loss of moisture combined with changes in temperature causes physical changes in the structure of woven fabrics. The swelling and shrinking of fibres, if repeated, leads finally to irreversible changes in size: to the stretching or shrinking of the fabric. The presence of light and oxygen causes chemical changes in the structure of threads and fibres. The degradation is also accelerated by the presence of moisture and UV radiation. Exposure to ultraviolet and visible radiation causes fibres to turn yellowbrown or fade before final decomposition into powder. Ultraviolet radiation causes a process of photo-oxidation that continues even after the light is removed. The discoloration does not in itself weaken the material, but acids formed simultaneously draw off the natural moisture-content of the fibres, as a result of which the textile dries up and falls finally to dust. 16 Enzymes produced by microorganisms cause the biological decomposition of fabrics. Fungi and bacteria alter the chemistry of their surrounding environment. Both cause characteristic greenish-brown discolorations, and lead finally to the complete decomposition of the material. 17 An acidic environment is harmful to linen and cotton; the animal fibres wool and silk suffer from alkaline conditions. But due to chemical changes the degraded fibres are sensitive to both the alkaline and acidic conditions which will change their mechanical properties. The decomposition of archaeological textiles is extremely complex and apart from the above-mentioned factors their condition is influenced by number of other things, including burial practices, soil chemistry, the mechanical effect of fabrication or wearing and the circumstances of excavation. 18 This accounts for the fact that the condition of material recovered from the ground is always worse than that of unburied fabric. The decomposition of textiles is a natural process which can only be slowed by the creation of appropriate storage conditions, but can never be wholly stopped. It will be clear, then, that the handling of archaeological textiles demands special attention in every case. Their condition excludes any sort of radical chemical or mechanical treatment. In such circumstances it will become clear why we did not regard the conservation of about 180 fragments of ancient textiles as an everyday task. 16 Sipos, E., Archeological Textiles, MS, forthcoming. 17 Sibley, L.R. - Jakes, K.A., Survival of Protein Fibres in Archeological Contexts, Science and Archeology 26 (1984) p. 23. 1X Janaway, R.C., Dust to Dust: The Preservation of Textile Materials in Metal Artefacts Corrosion Products with Reference to Inhumation Graves, Science and Archeology 27 (1985) pp. 29-34.