AIC's 45th Annual Meeting

The need to consolidate a painted gypsum plaster surface on a Kizil wall painting fragment presented distinct challenges. The gypsum finishing layer on a mud and straw support is matte in appearance, and had been previously consolidated with a non-aqueous hydrophobic material. This earlier treatment resulted in the inability to use an aqueous material such as funori, and spurred a search for alternate solvent-based consolidants. Polyvinyl butyral polymers (PVBs), often used on many organic materials and as a consolidant for archaeological wood and bone, were recommended as a possible alternative, however, there were concerns regarding the long term ageing and stability of the material. As a result, a research project was undertaken to build on the previous work by Feller and others. Cast films of Butvar B-76, Butvar B-98, Mowital B30H and Acryloid B-72 (the widely used acrylic copolymer) were investigated before, during and after exposure to ultraviolet light. Additional samples underwent accelerated aging in a Weather-ometer that simulated indirect daylight filtered through pane glass. Property changes were assessed using fiber optic Fourier Transform Infrared spectroscopy (FTIR), color measurements, solubility tests and visual examination. UV and simulated daylight samples exhibited similar changes. PVB samples yellowed slightly with exposure, showed an increase in oxidation concurrent with film weight loss, and remained removable with ethanol suggesting lack of cross-linking. The degradation rate depended on the particular PVB formulation, though the exact cause was not determined. To test the effectiveness of the materials in a situation more analogous to the wall paintings that initiated the project, samples of plaster were consolidated with each of the resins being studied. These also were exposed to UV light and measurements were carried out similarly to those on the films. Due to penetration into the plaster and shielding effects of this material, discoloration was not observed after UV exposure and the films remain readily removable by mild organic solvents such as ethanol.