Cleaning of Watercolour Drawings A study of the use of Gellan gum gel on water sensitive media

Abstract

Gellan gum is a non-toxic and biodegradable polysaccharide widely used in pharmaceutical and food industries. 2003 the use of a rigid gel of Gellan gum was introduced in paper conservation for cleaning of works of art on paper. The method has been thoroughly evaluated and highlighted as an ideal method for treating sensitive and degraded papers. This study aims to evaluate the suitability of the method on watercolour drawings. This study comprises a comparison between cleaning with Gellan gum gel and washing by immersion. An experiment has been conducted on paint-outs of six historic madder lake pigments and three historic Prussian blue pigments together with one modern synthetic pigment painted onto three different papers. Evaluation of eventual changes of the media during treatment has been made with respect to colour change, morphological changes i.e. loss of colour and redistribution of pigments, and migration of pigments into the paper matrix using colorimetry, UVvis spectroscopy, absorption spectroscopy and microscopy. The results indicate that there are a significant difference between gel cleaning and immersion wash. Regarding the risk for colour change due to pigment loss, gel cleaning is preferable, as long as no top layer is added to the cleaning sandwich. Regarding wash fastness, cleaning with Gellan gum gel has proved to increase morphological changes.