GC/MS Investigations of Varnish Removal on Oil Paintings with Gelled Surfactant-Free Emulsions Made from Xanthan Gum and Benzyl Alcohol

Over the last two decades, gelled surfactant-free emulsions containing benzyl alcohol have been commonly used in conservation for the removal of organic film-formers. The assumption that the strong solvent power of benzyl alcohol is mitigated precisely by its presence in moderate quantities in an aqueous environment has not yet had analytical confirmation. However, the low volatility of the solvent, and its strong swelling action on the oil binder, prompted this analytical verification. At a theoretical level, the saturation of the surface with Cyclomethicone D5 siloxane appears like a good strategy to reduce the diffusion of the solvent and decrease the interaction with the paint medium. This method was originally developed twenty years ago to allow the aqueous cleaning of acrylic paints: thanks to its complete immiscibility with water, siloxane acts as a temporary hydrophobic barrier, to repress diffusion and capillarity. Furthermore, D5 also appears immiscible with benzyl alcohol; therefore, it could act as a double barrier, towards water and alcohol. In this study, samples of an oil painting, treated with gelled emulsions containing benzyl alcohol with and without pre-saturation with D5 for varnish removal, were analyzed through GC/MS to monitor leaching and through SEM to highlight alterations in the surface morphology.