Analysis of plant gums and saccharide materials in paint samples: comparison of GC-MS analytical procedures and databases

Abstract

BackgroundSaccharide materials have been used for centuries as binding media, to paint, write and illuminate manuscripts and to apply metallic leaf decorations. Although the technical literature often reports on the use of plant gums as binders, actually several other saccharide materials can be encountered in paint samples, not only as major binders, but also as additives. In the literature, there are a variety of analytical procedures that utilize GC-MS to characterize saccharide materials in paint samples, however the chromatographic profiles are often extremely different and it is impossible to compare them and reliably identify the paint binder.ResultsThis paper presents a comparison between two different analytical procedures based on GC-MS for the analysis of saccharide materials in works-of-art. The research presented here evaluates the influence of the analytical procedure used, and how it impacts the sugar profiles obtained from the analysis of paint samples that contain saccharide materials. The procedures have been developed, optimised and systematically used to characterise plant gums at the Getty Conservation Institute in Los Angeles, USA (GCI) and the Department of Chemistry and Industrial Chemistry of the University of Pisa, Italy (DCCI). The main steps of the analytical procedures and their optimisation are discussed.ConclusionsThe results presented highlight that the two methods give comparable sugar profiles, whether the samples analysed are simple raw materials, pigmented and unpigmented paint replicas, or paint samples collected from hundreds of centuries old polychrome art objects. A common database of sugar profiles of reference materials commonly found in paint samples was thus compiled. The database presents data also from those materials that only contain a minor saccharide fraction. This database highlights how many sources of saccharides can be found in a paint sample, representing an important step forward in the problem of identifying polysaccharide binders in paint samples.

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

“…In these samples though, saponification, if it occurred, was not complete, as the ν as COO − bands of the glycerolipid materials were still very well visible in the spectra, and the ν as COO − bands of the lead carboxylates, if present, were not distinguishable from the amide II band. The sugar profiles that were observed were in perfect agreement with the presence of egg [18].…”

“…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].…”

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

“…Results from a previous stage of this research showed that sugars are found in many materials that can be encountered in a paint sample, such as organic colorants, plant resins and proteinaceous binders [28]. This indicates that a mixture of binders, which is extremely common in paintings, may lead to chromatogram profiles that are difficult to interpret when the overall composition of the organic materials is unknown.…”

“…In a previous stage of this research, it was suggested that the presence of a pigment in a paint layer containing a polysaccharide gum might cause modifications upon ageing [28]. For this reason, the effect of ageing in the presence of some pigments was investigated.…”

What do we know of Roman wall painting technique? Potential confounding factors in ancient paint media analysis

“…Most studies of ancient binders acknowledge considerable difficulties in accurate identification due to the degradation of the original compounds, the mixture and interaction of materials present in the preparation, paint and protective layers, and the small sample size [25][26][27]. Besides these factors, often taken into account in such studies [28][29][30][31][32][33][34], are two other factors, not usually considered in literature, which may have a decisive influence on results: the difficulty in efficiently extracting organic binders from ancient paint samples, and the presence of organic material due to microbiological contamination.…”