Methods for the deacidification of canvas paintings were reported which are with calcium hydroxide in water, magnesium bicarbonate in water and magnesium methoxy methyl carbonate in methanol and trifluorochloroethane. The main difficulty, the acid catalyzed degradation mechanism, can be stopped if the acids are neutralized. However, these subjects were not part of the study and are excluded. Ĭellulosic materials can also be degraded thermally, by photolysis and by microorganisms or fungi. Another aspect is the oxidative degradation which occurs if the painting layer contains heavy metal ions as iron or copper. As a result, there will be serious damages in the fabrics. If no neutralization of the acids takes place, the fibers of the canvas become more and more brittle. The main reasons for the degradation of cellulosic material are acid catalyzed hydrolysis and degradation by sulphur dioxide and nitric oxides from air pollution. In addition, acidity may come from the degradation of the cellulose itself or the polluted environment. Out of the manifold layers of the canvas, there may be migration of acids from varnishes or binding materials through the canvas. All these painting supports have in common that they consist of cellulosic material. This work focused on canvasses of easel paintings which are made of cotton, jute or linen. The stabilization film also needs to have the lowest possible weight, to avoid any further mechanical stress or damage caused by extra added weight. To prevent any tension in the canvas, the elasticity and reaction to humidity changes of the stabilization film need to be similar to the ones from canvas or even less. This can be achieved with a short contact time of the solvent and the canvas, either by a very low solvent concentration or with a high volatile solvent.įurthermore, the treatment shall achieve a high stabilization of the canvas. The challenge was to develop a system for deacidification- and stabilization which has none or as few as possible negative side effects on the object. Nonpolar solvents affect the binders of oil paints and varnishes. Polar solvents like water make the fibers swell and can dissolve the colored degradation products of the canvas. The whole system of canvas and paintwork is extremely sensitive against any type of solvents. The degradation processes cause disruptions and cracks which endanger the paintwork of the entire picture.ĭue to the manifold used substances, there are several main difficulties in developing an appropriate treatment. But the canvasses of many paintings have also become very weak by oxidative and acid-catalyzed degradation reactions in the past centuries. Problems included yellowed varnishes, flaking of the painting layer, craquelure and others. So far, the restoration of canvas paintings has often concentrated on the face of the painting. The deacidification agents showed an increase of pH from acidic to alkaline after the treatment and a deposition of an alkaline reserve. The deacidification of canvasses is a good preventive measure and can protect canvasses from future damage by acidity. The application of these products showed a good increase of breaking force at a low increase of the mass of the canvas and also had only slight optical changes of the canvas. Each product was applied to highly degraded, acidic model cotton canvas as well as canvas from real paintings. The nonpolar products were obtained by the silylation of the raw materials and allow the solubility in nonpolar solvents as heptane. The polar components are hydroxyethyl methyl cellulose and nanocrystalline cellulose which are biopolymers derived from renewable raw materials. The deacidification agents are sub-µm-particles of calcium carbonate or magnesium oxide which are dispersed in water or heptane. The treatment should be applicable to the back side of the canvas. Because of the diversity of painting types, two product groups which have polar and nonpolar character were developed. The aim of this study was to develop new, sustainable treatments for the consolidation and conservation of canvas of modern and contemporary art.
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