art conservation and restoration
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art conservation and restoration
Works of art are subject to a variety of disfiguring ills, many of them caused by environmental effects, particularly temperature and humidity changes and pollution. Much modern conservation effort is directed toward producing a stable, favorable situation for the display of art works and maintaining regular inspection and diagnostic procedures to combat deterioration. Techniques for this inspection have become increasingly sophisticated; they currently involve photographic, X-ray, infrared, and other radiation examination, as well as complex chemical analysis.
All effective art conservation and restoration ultimately depend upon the restorer's understanding of materials, technical craftsmanship, and aesthetic and historical awareness. The support (such as wood panel, canvas, paper), the ground (gesso, chalk), and the surface treatment (wax, varnish) of a painting all undergo some form of decay over the years.
Frescoed walls absorb moisture from the atmosphere. The moisture carries to the wall soluble surface salts that effloresce and injure the fresco pigments. To halt such injury water-permeable fixatives may be applied to help stabilize the pigment and prevent it from flaking off. A more drastic treatment is transfer, by which the mural and upper layer of plaster are cut away from the wall altogether and made fast to a new support. A major instance of successful transfer was carried out on many frescoes unearthed at Pompeii.
Wood-panel paintings undergo much swelling and shrinking with humidity variations. Wood-boring insects and the dry rot of fungus also attack them. The painting may be transferred to a new support, or the old one may be strengthened by impregnation with a consolidating medium (including several plastics) or given auxiliary support. Insecticides and fungicides may suffice to combat woodworms and dry rot; in cases of advanced destruction, reinforcement by impregnation may be necessary.
Canvas supports also absorb and lose moisture, swelling and shrinking, and thereby losing much pigment. In addition, canvases may be weakened or torn with comparative ease. A method of relining (restretching on a second undercanvas) may be effected whereby the old canvas is attached to the new by means of an adhesive. This may be a thermoplastic wax-resin combination or a water-base glue. The painted surface becomes impregnated with the adhesive and is consequently stabilized.
Irregular staining, called foxing, is the bane of print and drawing collectors. In humid conditions foxing attacks the adhesives and mounts of paper-based art, including watercolors, by producing the nutrients favored by molds present in the atmosphere. The work may sometimes be sterilized and remounted on a support chosen for its mold-repellent quality. It may be further treated with a fungicide. Some foxing stains may be removed by careful bleaching and washing, but this is a difficult technique requiring considerable knowledge of materials.
Restoration of Sculpture
Sculpture, especially that which stands outdoors, is particularly vulnerable to environmental changes. Placing the sculpture in a temperature- and humidity-controlled situation is the best means by which to preserve it. Stone sculpture requires periodic washing; either steam, spray, or trickled water is used, depending on the porosity of the stone. Soap, but not detergent, may also be applied. Broken sculptures may be mended with clear, cold-setting adhesives, sometimes mixed with a suitably colored filler, or by means of dowelling. Large pieces of sculpture are held together with metal dowels, usually of copper, stainless steel, or brass.
Broken wood sculpture is also dowelled, as is ivory, and special cements may also be used to fill cracks. Wood sculpture is also vulnerable to woodworm and dry rot and may be treated with insecticide and fungicide. Badly decayed wood works may sometimes be preserved by means of impregnation with a plastic medium.
Metal sculpture may be waxed to protect it from atmospheric corrosives. Bronze acquires a patina, or irregular surface pattern caused by deposits of sulfides and oxides, that is widely considered aesthetically pleasing, whereas patina on lead objects results in eventual decay. Cracks in metal sculpture may be filled with special adhesives. Corrosion may be halted by electrolytic reduction, which, however, destroys patina. Various chemical solvents and mechanical techniques are used to remove specific incrustations.
See H. J. Plenderleith and A. E. Werner, The Conservation of Antiquities and Works of Art (2d ed. 1971); Francis Kelly, Art Restoration (1972).