Joy Mazurek

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

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.

Py-GC/MS applied to the analysis of synthetic organic pigments: characterization and identification in paint samples

AbstractA collection of 76 synthetic organic pigments was analysed using pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The purpose of this work was to expand the knowledge on synthetic pigments and to assess characteristic pyrolysis products that could help in the identification of these pigments in paint samples. We analysed several classes of synthetic pigments not previously reported as being analysed by this technique: some metal complexes, β-naphthol pigment lakes, BONA pigment lakes, disazopyrazolone, triarylcarbonium, dioxazine, anthraquinone, indanthrone, isoindoline and thioindigo classes. We also report for the first time the Py-GC/MS analysis of a number of naphthol AS, benzimidazolone, phthalocyanine and perylene pigments and other miscellaneous pigments including pigments with unpublished chemical structure. We successfully used the Py-GC/MS technique for the analysis of paints by artists Clyfford Still and Jackson Pollock to identify the synthetic organic pigments and the binding media. Graphical AbstractPyrogram of PR49, with fragments produced by pyrolysis

The Development of a New Analytical Model for the Identification of Saccharide 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.

Composition and Condition of Naturally Aged Papers

Abstract The properties of forty naturally aged papers taken from books dating from 1477 to 1793 were assessed using two indicators of paper condition: degree of polymerization and yellowness index. These data were interrelated with three variables that may impact long-term paper stability: pH, gelatin content, and residual metals content. More stable specimens (high degree of polymerization and low yellowness index values) were strongly associated with high pH. High pH specimens were found to contain lower amounts of aluminum, potassium, and sulfur, as well as higher amounts of calcium and magnesium. Papers with more than 5.5% w/w gelatin content exhibited high pH, while those containing less than 5.5% w/w gelatin content showed both a range in pH and a broad range of aluminum, potassium, and sulfur content. Consequently, high gelatin content specimens were in good condition while low gelatin content specimens ranged in condition from poor to good. Results suggest that pH is the controlling factor in long-term stability and that gelatin needs to be present above some content level to provide long-term stability. The origin of high pH may lie in the alkaline calcium and magnesium residues.

Pyomelanin production in Penicillium chrysogenum is stimulated by L-tyrosine.

From a tomb in Upper Egypt we isolated a strain of Penicillium chrysogenum that was capable of producing brown pigment in vitro when grown in a minimal salts medium containing tyrosine. We present evidence that this pigment is a pyomelanin, a compound that is known to assist in the survival of some micro-organisms in adverse environments. We tested type strains of Pe. chrysogenum, which were also able to produce this pigment under similar conditions. Inhibitors of the DHN and DOPA melanin pathways were unable to inhibit the formation of the pigment. Fourier transform IR analysis indicated that this brown pigment is similar to pyomelanin. Pyrolysis-GC/MS revealed the presence of phenolic compounds. Using LC/MS, homogentisic acid, the monomeric precursor of pyomelanin, was detected in supernatants of Pe. chrysogenum cultures growing in tyrosine medium but not in cultures lacking tyrosine. Partial regions of the genes encoding two enzymes in the homogentisic acid pathway of tyrosine degradation were amplified. Data from reverse-transcription PCR demonstrated that hmgA transcription was increased in cultures grown in tyrosine medium, suggesting that tyrosine induced the transcription.

LIFTING THE LIDS OFF RIPOLIN: A COLLECTION OF PAINT FROM SIDNEY NOLAN'S STUDIO

Abstract A collection of 30 cans of Ripolin paint in 19 different tints from the studio of Australian artist Sidney Nolan provides a unique reference set for the study of this brand of paint. The cans date broadly to the period 1935–1953. All the Ripolin paints in cans from this study were manufactured at the companys English factory in Southall, London, which commenced manufacture in 1932. The paint is of two types, flat and gloss, in a range of colors. Observations made during opening, painting out, and drying the paint have provided information on its working properties. The flat paints with a large proportion of volatile solvents were quick to become touch-dry, whereas the thicker oily liquids present in the gloss paints took up to several weeks to lose tackiness. This observation is supported by Nolans own frustrations regarding the slow drying of Ripolin. Instrumental analysis has identified the pigments present in each color tint. By using Meth-Prep GC-MS on 10 samples, the presence of heat-bodied drying oils and a fatty acid marker for castor oil in one color were detected. Copal and colophony resins were also identified in a number of colors. The highly oxidized state of the resins suggested significant heat treatment during processing.

DICTATED BY MEDIA: CONSERVATION AND TECHNICAL ANALYSIS OF A 1938 JOAN MIRÓ CANVAS PAINTING

Abstract Groupe de Personnages (1938), a canvas painting created in Paris during the Spanish Civil War, required stabilization prior to exhibition. Upon examination, flaking paint and tiny spherical protrusions within those paint layers were identified. A project was initiated to determine materials that could have contributed to the current state of this painting. Because Groupe de Personnages had not undergone harsh conservation treatments this was a unique opportunity to study Mirós techniques and materials from a period of great artistic experimentation. Scientific analysis revealed the identity of pigments and the presence of zinc soaps. In addition, because Miró was a prolific writer, evidence was found in his letters, studio notes and interviews to corroborate analytical results – contributing to a more complete understanding of his artistic intentions and the conservation-related consequences of his selected materials.

ULTRAVIOLET-INDUCED VISIBLE FLUORESCENCE AND CHEMICAL ANALYSIS AS TOOLS FOR EXAMINING FEATHERWORK

Abstract Feathers are found in cultural heritage collections of tribal arts from the Americas, Africa, and the Pacific as well as in contemporary art, European and American fashion, and in taxidermy and ornithology specimens. Although museum conservators routinely evaluate feathers by looking at insect damage and mechanical wear, as well as fading as evidence of light exposure, examination of feathers for visible fluorescence under an ultraviolet source is atypical. Recent research by both the authors and bird biologists indicate that ultraviolet fluorescence examination can provide valuable information about the identification and pigmentation of feathers found in museum collections. A number of feather pigments, including psittacofulvins found only in red and yellow pigments in birds in the Psittaciforme family, as well as porphyrins found in rusty brown owl plumage, may be identified by their specific ultraviolet-induced visible fluorescence. Feathers whose pigments are not directly fluorescent may still undergo appearance changes under an ultraviolet source as a consequence of light aging. Fluorescence is demonstrated to be an early marker of chemical change, and can be used to detect such change before it can be measured colorimetrically. The authors evaluate different methods of analysis, including ultraviolet-induced visible fluorescence, reflectance spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, gas chromatography/mass spectroscopy, and rates of pigment extraction for detecting light-induced physical and chemical changes in feathers. Results indicate that ultraviolet-induced visible fluorescence may be the most sensitive indicator of light-induced degradation. Museum featherwork, some with records of estimated display, was found to display ultraviolet-induced visible fluorescence changes analogous to photoaged feather samples.