An Investigation of the Feasibility of the Use of Gels and Emulsions in Cleaning of Gilded Wooden Surfaces. Part A: Removal of Brass-Based Overpainting

The term ‘cleaning of gilded wooden surfaces’ should be understood broadly to account for their complexity. Each layer of a gilded surface requires assessment, and often, a separate cleaning methodology. Removal of overpainting is a part of the surface cleaning process of gilded wood. Many cleaning methods for gilded surfaces were adopted from other conservation fields, as there is little research in reference to cleaning of gilded wood. Two case studies involving nineteenth century gilded frames, focused on finding a suitable gel and application method to remove brass-based overpainting and surface dirt. This paper presents the findings from our investigation in regards to brass-based overpainting removal (Part A). The results of experiments into removal of soiling from gilded wooden surfaces are covered in a second paper (Part B). Two rigid gels reviewed in conservation literature were tested for removing brass-based overpainting from oil-gilded surfaces: Xanthan gum gel and poly(vinyl alcohol)-borax gel (PVOH-borax gel). Low-viscosity emulsions based on Pemulen TR-2 were also tested as they involve more straightforward clearing process than with viscous gels. Gels were evaluated according to application and removal methods, viscosity, texture, and cleaning efficiency. Rigid solvent gels and low-viscosity emulsions offer a viable alternative to free solvent application provided they can be easily removed from the surface, with minimal clearing requirements. Factors influencing the performance of gel systems include the thickness of the overpainting layers, the presence of a ‘barrier layer’ between the overpainting and gilding, the solubility of the overpainting binder, and the solubility characteristics of the solvent (its rate and power of swelling, evaporation rate and application method). For the removal of overpainting from gilded wooden surfaces, fast-acting solvents with moderate swelling power are more appropriate than slow-acting solvents with strong swelling power. The latter can soften gilding layers beneath the overpainting. Important factor to consider are solvent volatility and the rate it diffuses into the overpainting.