The Use of Gels for the Removal of Cellulose Nitrate Lacquer on Silver

Abstract

The conservation of silver objects mainly constitutes addressing the issues of tarnish removal and of preventing tarnish. For decades lacquer has been used to coat silver objects in order to protect them from tarnishing. However, the degradation of coatings causes an uneven tarnishing and a corrosion that can propagate under the coating layer, thus destabilizing the silver object. To remove the coatings, extensive amounts of volatile solvents are used, which put a stress on both the conservator performing the treatment and to the environment. This thesis aims to investigate if the use of different types of gels, an eco-friendly agar gel and a polyvinyl acetate (PVA) high-viscosity polymeric dispersion (HVPD), can be used to remove coatings effectively, while also reducing the use of volatile solvents. Experiments were performed on unaged and aged silver coupons coated with nitrocellulose lacquer. Four different agar-gels, loaded with different volumes of either acetone or ethyl acetate, and one PVA-gel loaded with a microemulsion were used in attempts to remove the coatings on the silver coupons. Discussion regarding the impact of choice and concentration of solvent, application time, the question of residue and consequences of mechanical action for clearance of gels, follows the results of the experiments. The study concludes that it is possible to remove aged nitrocellulose coatings from silver with the use of agar 2% (w/v) loaded with 40% acetone:ethanol (1:1), but that further or complementary treatments need to follow to address the issue of residues. Therefore, a reduction in use of volatile organic solvents can be accomplished within the treatment of lacquer removal from coated silver.