Evaluation of mucilage efficacy in the removal of a natural adhesive (gacha) from a canvas by ATR–FTIR. First results

Abstract

Nowadays the use of gelled systems to remove natural glues from cultural artefacts is very common, as they allow the application of controlled humidity to sensitive surfaces. These cleaning systems can be of natural or synthetic origin. The simplest gelled systems are made by adding a gelling agent (such us Laponite® RD, xanthan gum or agar-agar) to the cleaning agent. The aim of this research is to evaluate, using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR), the efficacy of hydrogels prepared from three commercial natural mucilages: guar, locust bean and konjac, in removing gacha from the reverse side of a canvas, and following the nowadays tendence that try to use eco-sustainable and bio-renewable cleaning materials. Gacha is an adhesive, made commonly with flour and animal glue as the main ingredients, used to line canvas paintings. The gels prepared were characterised by means of pH, electrical conductivity (EC), viscosity and aqueous phase release capacity. For this study, a mock-up of the canvas and the adhesive was prepared. Two application methods for the gels were tested: direct application and indirect using a physical barrier, with contact times of 15 and 30 min. The suitability of the mucilages in the elimination of the natural adhesive has been related to the decrease of the content of gacha on one side, and to the absence of gel residues after the cleaning process on the other, both parameters evaluated with ATR-FTIR analysis complemented with microscopic observations. The obtained results indicated that the removal of gacha was more effective with direct application, regardless of the mucilage used. On the other hand, mucilage residues are, in general, not significant, although in the case of direct application of guar and konjac for 15 min and locust bean and konjac for 30 min, the presence of mucilages traces were detected.