The Development of a New Analytical Model for the Identification of Saccharide Binders in Paint Samples

Abstract

This paper describes a method for reliably identifying saccharide materials in paintings. Since the 3rd millennium B.C., polysaccharide materials such as plant gums, sugar, flour, and honey were used as binding media and sizing agents in paintings, illuminated manuscripts, and polychrome objects. Although it has been reported that plant gums have a stable composition, their identification in paint samples is often doubtful and rarely discussed. Our research was carried out independently at two different laboratories: the Getty Conservation Institute in Los Angeles, USA (GCI) and the Department of Chemistry and Industrial Chemistry of the University of Pisa, Italy (DCCI). It was shown in a previous stage of this research that the two methods give highly comparable data when analysing both reference paint samples and paint layers from art objects, thus the combined data was used to build a large database. In this study, the simultaneous presence of proteinaceous binders and pigments in fresh and artificially aged paint replicas was investigated, and it highlighted how these can affect the sugar profile of arabic, tragacanth, and fruit tree gums. The environmental contamination due to sugars from various plant tissues is also discussed. The results allowed the development of a new model for the reliable identification of saccharide binders in paintings based on the evaluation of markers that are stable to ageing and unaffected by pigments. This new model was applied to the sugar profiles obtained from the analysis of a large number of samples from murals, easel paintings, manuscripts, and polychrome objects from different geographical areas and dating from the 13th century BC to the 20th century AD, thus demonstrating its reliability.

Transylvanian glass icons: A GC/MS study on the binding media

“…The presence of mannose is the result of the contribution of the saccharide fraction of egg [17], in agreement with the results from the amminoacidic fraction (see above). On the contrary, the qualitative profile of sample XIII-2 containing arabinose, mannose and galactose as well as higher saccharide content, seem to point to the presence of an unidentified saccharide material [16]. The presence of rhamnose in sample XIV-4 could allow hypothesizing the presence of Arabic gum in the sample.…”

“…In almost all samples, the high content of xylose and glucose, as well as the low saccharide content, points to a profile corresponding to environmental contamination from the wood of the frame or the back cover or accumulated dust (Table 4) [16]. The presence of mannose is the result of the contribution of the saccharide fraction of egg [17], in agreement with the results from the amminoacidic fraction (see above).…”

GC/MS and proteomics to unravel the painting history of the lost Giant Buddhas of Bāmiyān (Afghanistan)

“…Saccharide material was found in some of the samples, and the sugar profiles obtained from each sample analysed are presented in S3 File. Tragacanth gum was identified on the basis of the presence of fucose in the samples [29]. …”

Characterisation of preparation layers in nine Danish Golden Age canvas paintings by SEM–EDX, FTIR and GC–MS

“…The xylose/arabinose ratio was higher than one, and fucose was absent. Therefore, we can exclude the presence of tragacanth gum and suggest the presence of fruit tree or gum arabic [19], which could very well serve the similar purpose of providing flexibility; alternatively, it could have been used as a sizing agent for the canvas. KMS3262 and KMS1671 seem quite similar in material composition in the analyses that have been used here, and the two paintings were also painted more or less at the same time but by two different artists.…”

“…Elements in parentheses are present at trace levels. Pb (lead), Ca (calcium), Al (aluminium), Si (silicon), Fe (iron), Na (sodium), Mg (magnesium), K (potassium), S (sulphur), and Ba (barium) To determine the source of the saccharide materials, the data were compared to a database of saccharide profiles of reference materials [18], and when polysaccharide gums were hypothesised, they were identified using a decisional scheme that was reported in the literature [19]. The interpretation of the chromatograms relative to the lipid-resinous fractions was based on the recognition of molecular markers for resins and waxes and quantitative evaluation of mono and dicarboxylic acids for lipids [20].…”