Analytical evaluation of gelatin removal from ancient papers induced by wet cleaning: a comparison between immersion treatment and application of rigid Gellan gum

In paper conservation, wet cleaning treatments are usually performed to remove harmful degradation substances. Although cleaning treatments are fundamental in this field, the use of free water, besides causing an excessive swelling of cellulose fibres and sometimes also strong alterations of graphic media, could induce the extraction of the original sizing agents, resulting in a weakening of the paper structure. Rigid polysaccharide hydrogels (i.e. Gellan gum) can be effectively used to minimize the impact of water on paper. The present study evaluates the rate of gelatine removal from paper artworks comparing two different wet cleaning treatments: washing by immersion in free deionised water and by means of Gellan gum application. After a preliminary characterization of the paper samples through Hertzberg stain test and Fourier Transform Infrared Spectroscopy (FT-IR), the study is carried out using Gas Chromatography - Mass Spectrometry analysis (GC-MS). The results showed that Gellan gum was less invasive than immersion treatment since it caused the extraction of lower amounts of gelatine from paper. The gelatine removal was also tested by statistical analysis, in particular Principal Component Analysis (PCA) of amino acids.