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An Investigation into the Chemistry and Removal of Unrefined Shellac from Ceramic Substrates via Hydrolysis


For more than 200 years, shellac has been used in the repair and mending of ceramic materials. Over time, the shellac becomes brittle and the joins begin to fail, requiring retreatment. The removal of shellac from previous repairs presents a number of problems to conservators, as this resin is not easily soluble in solvents. To further complicate the removal process, recent research at the J. Paul Getty Museum has revealed that the use of fumed solvents for the removal of unrefined shellac causes the lac dye component of the resin to go into solution, absorb into the porous substrate of the ceramic fabric, and, through a complex chemical reaction, form an organometallic complex with metallic impurities in the ceramic, causing an irreversible purple-pink colored stain.

This study has sought new methods and materials for the removal of unrefined shellac, particularly from porous substrates. It explores the use of alkaline solutions, held within a gel support, as a method of hydrolyzing rather than solubilizing the resin, in order to prevent staining altogether. The results of experimentation have found that the use of sodium hydroxide (NaOH) in conjunction with ethanol, held in a rigid gel support composed of agar, effectively breaks down the resin molecules while preventing or minimizing staining from the lac dye component. Though more research remains to be done in order to refine the methods and materials, this study represents a starting point for a new direction in shellac removal techniques in conservation.

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