Cleaning of water-gilded surfaces using hydro- and solvent-gels

This paper describes the implementation of three customized gels on a 19th century panel painting for the removal of its degraded natural resin varnish from a water-gilded surface and a complex solvent-sensitive stratigraphic construction over the gilded substrate. At first, the varnish was unsoiled with a typical hydrogel that was composed of an aqueous phase buffered at pH 5.5 with sodium acetate, poly(ethylene glycol) p-(1,1,3,3-tetramethylbutyl)-phenyl ether surfactant and hydroxy-prorylmethyl cellulose. The removal of the entire aged varnish was facilitated with a microemulsion of an aqueous phase buffered at pH 8.5 with triethanolaminate, a fatty phase of a mineral spirit - benzyl alcohol solution and a polyoxy-ethylene(23)lauryl ether surfactant, altogether incorporated in a viscous gel generated from the dissolution of a polyacrylic acid in poly(oxy-1,2-ethanediyl) cocoalkylamine surfactant. The third gel, which was based on a polyacrylic acid of higher viscosity and incorporating a microemulsion of the same aqueous phase (pH 8.5) as in the second gel, and a fatty phase made of benzyl alcohol and a polyoxyethylene(23)lauryl ether surfactant, enabled the selective removal of the degraded varnish over the elaborate gilded area with a composite stratigraphy over the golden leaf. Fourier transform infrared spectroscopy and UV fluorescence imaging were employed for the analysis of the aged varnish and the monitoring of the cleaning procedure, respectively. The conservation procedure determined the effectiveness of the customized gels employed for this special implementation. The fine preservation of the water-gildings and of the complex solvent-sensitive stratigraphic construction of the painted surface was a satisfactory outcome.