Removing ingrained soiling from medieval Lime-based wall paintings using Nanorestore Gel® Peggy 6 in combination with aqueous cleaning liquids

This paper describes a cleaning method for removing ingrained carbonaceous dirt from lime-based wall paintings by utilizing hydrogels in combination with aqueous cleaning liquids. Nanorestore Gel® Peggy 6 has a number of advantages over traditional cleaning methods, and it is capable of holding large amounts of liquid, but it limits liquid penetration into the substrate. Cleaning action occurs only at the interface, without affecting the surrounding area or leaving residues. Furthermore, its viscosity makes it an ideal tool for treating irregular, vaulted surfaces. Laboratory experiments conducted on limewashed model tiles were decisive in the design of in situ experiments on fifteenth-century wall paintings. The cleaning efficiency of each method was assessed and quantified using colorimetry, 2-D FTIR mapping and image analysis using Cultural Heritage ImageJ. SEM-EDX was used for seeking residues. Results of both the model and in situ cleaning tests show a significant reduction of ingrained dirt when comparing Nanorestore Gel® Peggy 6 to traditional methods. Best visual results were obtained when cleaning with hydrogel loaded with 5% triammonium citrate was following by swabbing with a wet sponge. However, using water alone with the gel yielded almost as good a result in situ, making cleaning possible without any risk of residues. © The International Institute for Conservation of Historic and Artistic Works 2020.