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Irreversible changes in paintings
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| Irreversible changes in paintings.
CRAQUELURE . The network of cracks apparent in most paintings, craquelure, develops as the medium dries, or as a result of movement of the dried, brittle paint film which occurs with age. This may be visually disturbing but cannot be corrected. YELLOWING . This occurs with all drying oils, such as linseed. It may cause color changes, particularly in pale areas and blues. PENTIMENTI . The increased transparency of the oil medium, as it ages, may result in changes made by the artist in the course of painting (pentimenti) be- coming visible through the upper paint layers. COLOR CHANGES . If fugitive pigments such as some red and yellow organic lakes have been used, they tend to fade under the action of light and cannot be restored. Green copper resinate often turns brown, and the blue pigment smalt may become gray in an oil medium. 104 In general, paintings are best kept framed and glazed, preferably with some backing to the frame to exclude dust. Paper. Paper is composed of cellulose fibers from rag or wood pulp. Its chief enemies are acidity and air pollution. ACIDITY . Acidity may result from the processing of wood pulp into paper and from the introduction of alum. A neutral pH of about 7 is ideal for paper, since excess alkalinity is also harmful. All deacidification processes are short- term measures, since acidity may also be increased by atmospheric pollution. LIGHT AND HEAT . The recommended light level for paper is 50 lux. High light levels may alter the color of paper but, more significantly, will fade pig- ments. High temperatures increase the rate of all chemical reactions; works on paper should therefore not be displayed too high on walls, over fires, or in di- rect sunlight. HUMIDITY . A level of 50 percent RH is recommended since fungus and mold thrive in high humidity, which should in any case never exceed 65 per- cent. Mold feeds on size, cellulose, and binders such as gum arabic or gum tra- gacanth which are used in watercolors and pastels. Insect pests tend to attack paper and glue, and may leave brown acidic deposits which eat into the paper. MOUNTING AND FRAMING . A major cause of deterioration of paper is mount- ing and framing on cheap board, which can transmit acidity to the paper, or on wood, which exudes resins into the paper. “Museum board” – high grade, acid- free board made from cotton fibers – should always be used. Paper must not be stuck down all over on to a board but hinged with good-quality Japanese paper, to allow expansion and contraction as atmospheric conditions vary. The mounting of works of art on paper protects them from unnecessary han- dling; the mount must also be deep enough to prevent the work from coming into contact with the glass when framed. This is particularly applicable to fragile pas- tel, chalk, and charcoal drawings which are highly susceptible to abrasion. Any treatment of fumigation, flattening creases, bleaching papers, mend- ing tears, or resizing should only be carried out by an expert, since it involves the use of moisture and toxic chemicals. жүктеу/скачать 0,79 Mb. Достарыңызбен бөлісу:
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