A Coptic art found expression through materials as diverse as earthenware, stone, metals, and textiles.
Individual pieces of art have been subjected to the ravages of time. Their preservation today poses problems specific to the materials of which the objects are composed, and to the milieu to which they belong, such as ancient collections and recent excavations. Under good conditions, meticulous cleaning and temporary repair preserve the object until it can be restored by a specialist.
The Copts used terra-cotta and unbaked clay for the manufacture of numerous utilitarian or liturgical objects. Their preservation requires a preliminary desalination, for the Egyptian subsoil in which they were covered contains a marked salinity.
For terra-cottas that are strong enough, with or without decoration, the operation consists of simple steeping in frequently renewed distilled water until all the soluble salts are removed. Very often it is necessary to strengthen porous ceramics by impregnating them with synthetic resin, or to protect a fragile decoration with a coat of soluble nylon.
For objects in unbaked clay the use of water is absolutely out of the question; the object must be consolidated. Soluble salts are extracted by using damp pads after applying a layer of soluble nylon, permeable to the salts but not to water.
On terra-cotta and unbaked clay, accretions insoluble to water are removed mechanically or chemically depending on their nature. For the assembling of fragments belonging to the same piece of pottery, it is advisable to use gums of a temporary nature. After the piece has been put together again, the gaps left by vanished fragments may be filled with other temporary materials such as plaster.
The beauty, diversity, and significant number of Coptic textiles have contributed in large measure to our knowledge of Coptic art. The fibers that make up these textiles are essentially linen, linen and wool, wool, and gradually silk at a later date. Careful examination of the fabric allows us to determine the nature of any stains and the tenacity of the dyes. Cleaning can be done in several ways: with distilled water or in softened water without iron and using a nonacidic soap (Lissapol), or, when the dyes are soluble in water or when there are fatty stains, by dry cleaning with the aid of solvents. The presence of mold requires sterilization by thymol vapor. It is sometimes necessary to treat for the removal of insects.
The Coptic fabric thus treated often requires mounting on acid- free backing, by sewing, or by thermocollage (for very brittle silks). For good conservation, the fabric should be screened from light between leaves of nonacidic paper, either flat or rolled, according to its dimensions.
The numerous Coptic objects made of wood or formed from various vegetable fibers often present similar problems of conservation. Wood and fibers are attacked by insects and by mold. The insects must be dealt with by fumigation in a vacuum with methyl bromide or by gamma rays, and the mold is removed by sterilization with thymol vapor. Fragile objects can be provisionally reinforced by impregnation with vinyl resin; final consolidation will be obtained through thermoplastic treatment by polymerization in a vacuum.
In the case of stuccoed wood, the layer of stucco, often crumbling, should be restored before treating the painted or decorated surface. The use of reinforcement on a polychrome Coptic wooden object need not entail any alteration in the colors.
The Copts inherited from ancient Egypt the use of papyrus as their main writing material. For a long time the major problem posed by this extremely fragile material was the unrolling of the precious manuscripts. Today, however, some museums prefer to keep the rolls intact; hence the most common work is the smoothing away of folds and creases in the papyrus so that the texts may be more clearly read.
There are several methods that allow a gradual and limited moistening of the fibers while preserving the ink and the colors. The papyrus that has recovered its elasticity can then be carefully flattened out and dried. The use of a fungicide preserves the document from mold. The different fragments of the same papyrus may be assembled by strips of rice paper glued to ordinary paper treated with fungicide. The cleaning and bleaching, when they are necessary, must be carried out by specialists. The preservation of papyrus requires that it be screened from ultraviolet rays.
The Copts also used parchment as a writing material. Methanol gives good results for removing folds and creases in parchment while preserving the ink. More specific treatment, such as cleaning, should be entrusted to specialists. The gum in parchment allows the different fragments of a single leaf to be pasted together. It is sometimes necessary to reinforce the page with rice paper when the parchment is very fragile.
Splinters of stone or pottery that served as writing material suffer above all from the presence of soluble salts. These salts can be removed either by the repeated immersion in distilled water or by the application of damp pads regularly renewed until all the salts have been extracted, care being taken beforehand to protect the ink with a layer of soluble nylon. Final reinforcement is achieved by the application of, or impregnation with, a synthetic resin appropriate to the material which does not alter the appearance of the ostracon.
Coptic Sculptures, Reliefs, and Architectural Fragments
When these are made of materials such as sedimentary rock (limestone), siliceous rock (sandstone), or carboniferous rock (bitumen), they often suffer chemical disintegration. Here again, preservation requires desalination, care being taken to protect by resins any colors and any surfaces that are too crumbly. According to the porosity of the rock, the final consolidation is achieved by impregnation with acrylic, polyester, or epoxide resin incorporating a fungicidal agent. In the case of a stone with several colors, the medium employed must not change the colors.
Work in metals and their alloys has enriched Coptic art with numerous objects and trinkets, but these are generally materials sensitive to chemical transformation due to the milieu in which they are or have been preserved. These items often show evidence of numerous alterations. Accretions covering an object may be removed either mechanically (by scraping or pricking) or chemically; in the latter case it is essential to determine the chemical constituents of the impurities.
After any treatment, the object, whose surface is highly reactive, should be protected from contact with the surrounding air by a screen of wax, paraffin, acrylic resin, or epoxide resin, depending on its porosity.
Numerous objects of clear glass and opaque glass suffer essentially from chemical changes. These changes are often accompanied by a disintegration caused by soluble salts. In fact, glass may become soluble in water through an excess of soda, and its decomposition may be furthered by excess of lime. Chemical treatment carried out by specialists can halt the process of disintegration and stabilize the glass. Thereafter the fragments of a single Coptic object in glass may be fitted together either by using a cyanoacrylate glue or an epoxy-type optic glue.
Hides and Skins
The Copts used hides and skins for clothes, footwear, and various objects. Skin disintegrates in humidity and it is equally sensitive to alkaline and acidic solutions; certain marine salts, alum, and tannin are favorable to its preservation. Lanoline, ox foot oil, or castor oil may be used to restore the elasticity of hides. Acetone fungicide may be used to remove organic deposits such as fungus and mold. Fumigation in a vacuum with methyl bromide or ethylene oxide will remove insects. Temporary reinforcement is ensured by impregnation with polyvinyl alcohol, while final consolidation requires a vinylic resin mixed with a fungicidal agent.
Bone and Ivory
Bone and ivory, from which the Copts manufactured numerous small objects, present different problems of preservation and conservation.
Fossilization of bone and ivory is frequent, through the association of the chalky matter they contain with the quartz and silica contained in the soil.
These materials are subject to great deformation in a humid milieu. In an acid environment, on the other hand, the osteine, which is an organic constituent, is attacked, reducing bone and ivory to a sponge.
Excellent results are obtained by mechanical or chemical treatments. Because of their fragility, the objects thus cleaned and treated must often be reinforced by resins.
MARIE-FRANÇOISE BOUILLET DE ROZIÈRES