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.

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.

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Understanding the original techniques in the creation of an artwork is a prerequisite for the selection of the most appropriate conservation method. This is particularly essential in wall paintings where control of potential agents of deterioration and efficient monitoring are limited due to the scale of the paintings and their exposure to uncontrollable environmental fluctuations. Analytical studies are increasingly focused on the investigation and study of degradation products of organic binders originally added in the paintings on a lime-based plaster ground. In the framework of IPERION-CH (Integrated Platform for the European Research Infrastructure ON Cultural Heritage) project, a collaborative task is dedicated to obtain knowledge about original organic materials used in wall paintings by evaluating and comparing different innovative methodologies and conventional diagnostic techniques used for the investigation of markers related to alteration mechanisms and degradation products. The non-invasive and microsampling methodology is first optimized on well-defined models that have been designed to simulate different painting techniques with limewater and five organic binders in different relative proportions. Future investigations will focus on the application of the optimized methodology on archaeological samples. In the present paper, preliminary results on a selected set of models, submitted in different stages of a wellestablished artificial ageing protocol, demonstrate the specific complementary input of each analytical technique included in the analytical approach (colour measurements, micro FTIR-ATR analyses in cross-sections, Evolved Gas Analysis-Mass Spectrometry and Gas Chromatography-Mass Spectrometry). The comparative evaluation and interpretation of the results is a step forward in the optimization of the approach and in relating the analytical findings detected on the analysed samples to the original compounds and the possible changes for each group of binders (proteins/gums) due to degradation or interaction depending on the pigment/metal ion present.

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