Francesca Modugno

Analytical Methods for the Characterization of Organic Dyes in Artworks and in Historical Textiles

Abstract Dyes are among the most significant components in works of art and archaeological findings. In the scientific examination of historical artefacts, the identification of natural dyestuffs is a challenging task, due to the complexity of their chemical composition and the possible presence of mixtures of chromophores and degradation products. For this reason, in the last few decades, new analytical procedures and techniques have been developed and improved for the characterization of organic dyes and their identification in microsamples. This review looks at the chemical composition of natural organic dyeing materials used in the field of the cultural heritage and focuses on several analytical methods based on spectrometric and chromatographic techniques that have contributed to the study of organic dyes in works of art and archaeological findings.

Characterisation of proteinaceous binders and drying oils in wall painting samples by gas chromatography-mass spectrometry

Abstract A reliable analytical procedure has been developed for the characterisation of drying oils and proteinaceous binders in samples of painted artworks. The method is based on microwave assisted acid hydrolysis followed by the extraction of the lipid component with diethyl ether. Fatty acids were determined after saponification of the organic phase and derivatisation with N-tert.-Butyl methylsilyl-N-methyltrifluoroacetamide. Amino acids present in the acid aqueous phase were derivatised with the same silyl agent. The separation and quantitative determination of derivatives was performed by gas chromatography–mass spectrometry. Detection limits of fatty acids (lauric, myristic, palmitic, stearic, oleic, suberic, azelaic and sebacic acid) and amino acids were in the range 50–100 pg. The mean recovery of the procedure for lipid determination was about 70% and that for proteins 100% with a reproducibility better than 10% for 1 mg samples. The overall procedure was validated by analysing suitable reference wall painting samples. The identification of the proteinaceous binders was achieved by principal component analysis performed on the fourteen amino acid relative percentages while the identification of the drying oils was based on the values of palmitic to stearic ratio and azelaic to palmitic ratio. A general pattern recognition scheme based on these values and on the amounts of dicarboxylic acids and the presence of cholesterol was developed to distinguish between proteinaceous binder, “tempera grassa” and drying oils. The application of the proposed procedure to samples from “The Legend of True Cross” (1452) by Piero della Francesca allowed the identification of “tempera grassa” made of egg and linseed oil.

Analytical Strategies for Characterizing Organic Paint Media Using Gas Chromatography/Mass Spectrometry

Throughout history, artists have experimented with a variety of organic-based natural materials, using them as paint binders, varnishes, and ingredients for mordants in gildings. Artists often use many layers of paint to produce particular effects. How we see a painting is thus the final result of how this complex, highly heterogeneous, multimaterial, and multilayered structure interacts with light. The chemical characterization of the organic substances in paint materials is of great importance for artwork conservation because the organic components of the paint layers are particularly subject to degradation. In addition, understanding the organic content and makeup of paint materials allows us to differentiate between the painting techniques that have been used over history. Applying gas chromatography/mass spectrometry (GC/MS) analysis to microsamples of paint layers is widely recognized as the best approach for identifying organic materials, such as proteins, drying oils, waxes, terpenic resins, and polysaccharide gums. The method provides essential information for reconstructing artistic techniques, assessing the best conditions for long-term preservation, and planning restoration. In this Account, we summarize the more common approaches adopted in the study of the organic components of paint materials. Our progress in developing GC/MS analytical procedures in the field of cultural heritage is presented, focusing on problems that arise from (i) the presence of mixtures of many chemically complex and degraded materials, (ii) the interference of inorganic species, (iii) the small size of the samples, and (iv) the risk of contamination. We outline some critical aspects of the analytical strategy, such as the need to optimize specific wet-chemical sample pretreatments in order to separate the various components, hydrolyze macromolecular analytes, clean-up inorganic ions, and derivatize polar molecules for subsequent GC/MS separation and identification. We also discuss how to interpret the chromatographic data so as to be able to identify the materials. This identification is based on the presence of specific biomarkers (chemotaxonomy), on the evaluation of the overall chromatographic profile, or on the quantitative analysis of significant compounds. GC/MS-based analytical procedures have for 20 years provided important contributions to conservation science, but challenges and opportunities still coexist in the field of organic-based paint materials. We give selected examples and provide case studies showing how a better understanding of the chemical composition of organic paint materials and of their degradation pathways contribute to a better knowledge our cultural heritage, and to its preservation for future generations.

GC-MS characterization of proteinaceous and lipid binders in UV aged polychrome artifacts

This paper presents the most significant results obtained from the characterization of protein and lipid binders in a broad range of reference paint materials prepared and stored at Opificio delle Pietre Dure in Florence (Italian Ministry of the Cultural Heritage, Italy). The amino acid distribution for protein binders and the fatty acid distribution for lipid binders were determined by gas chromatography-mass spectrometry before and after being artificially aged through exposure to UV light at 254 nm or 366 nm for different time periods in a climatic chamber (20°C and 80% RH). The results were compared with those relevant to old paintings of different ages, and showed that UV light aging does not significantly affect the amino acid profile of protein binders. Consequently, protein binders in old paintings can be reliably identified by comparing the amino acid composition with that of reference paint materials which have not been aged. However, the composition of lipid binders is substantially affected by UV irradiation, leading to a lowering of oleic acid and the formation of azelaic acid and other dicarboxylic acids including oxalic acid. An oleic to stearic acid ratio of less than 0.5 was observed in all the samples of works of art, and this parameter can be used to evaluate the extent of the artificial aging process. The formation of oxalic acid was also observed starting with pure unsaturated fatty acids, thus supporting the chemical origin of oxalate patina.

Two procedures for suppressing interference from inorganic pigments in the analysis by gas chromatography-mass spectrometry of proteinaceous binders in paintings

Abstract Two methods for suppressing the interference of inorganic pigments in the determination of amino acids in hydrolysates of wall painting samples by gas chromatography–mass spectrometry are described. One is based on the extraction of proteinaceous matter from the sample by a 2.5 M ammonia solution prior to the hydrolysis step, and the other on the elimination of inorganic ions from the hydrolysate by means of a cation-exchange resin. The proteinaceous binders present in the paint layer were identified using principal component analysis on the relative amino acid percentage. Some samples from “Giudizio Universale” in Florence Cathedral and from the Monumental Cemetery in Pisa (Italy), were analysed using both procedures. The presence of milk binder as the main organic component of the tempera was highlighted.

GC-MS characterization of paint varnishes

Abstract This paper presents an analytical procedure based on gas chromatography separation and mass spectrometric identification, which allows the determination of natural resins, waxes and lipids in the same microsample (

Characterization of the Balm of an Egyptian Mummy from the Seventh Century B.C.

Abstract An analytical procedure for the characterization of plant resins, waxes, bitumen, oils and their degradation products in mummy balms is described. The method is based on the selective extraction of these compounds from 19 samples with CH2Cl2 and, after drying the residue, with n-hexane, followed by a Florisil chromatographic clean-up step of the non-polar extract and by the saponification of an aliquot of dried CH2Cl2 extract. Polar compounds were derivatized with t-butyl-dimethyl silyl trifluoroacetamide (MTBSTF A). Quantitative determinations were obtained by gas chromatography-mass spectrometry. The procedure, tested on suitable reference materials such as beeswax and plant resins, showed a recovery of about 100% for non-polar compounds. Using this method, pine resins (P. pinea and P. sylvester), mastic resin (Pistacia lentisca and P. terebinthus), sandarac (Tetraclinis articulata), elemi ( Canarium), dammar (Hopea), myrrh (Commiphera) and a pine resin from the second century A.D. were characterized. Identification was based on the characteristic pattern of the diterpenoid and triterpenoid compounds contained in these natural products. Results on Egyptian mummy samples from the seventh century B.C. were obtained and showed that the main components used in the embalming process were mastic resin from the genus Pistacia, an unidentified vegetable oil, beeswax and bitumen. Terpenoids degraded by a thermal treatment were also found; therefore a hot fluid was used for embalming, confirming the practice hypothesized in the Late Period by egyptologists.

A multi-analytical study of degradation of lignin in archaeological waterlogged wood

Historical or archaeological wooden objects are generally better conserved in wet environments than in other contexts. Nevertheless, anaerobic erosion bacteria can slowly degrade waterlogged wood, causing a loss of cellulose and hemicellulose and leading to the formation of water-filled cavities. During this process, lignin can also be altered. The result is a porous and fragile structure, poor in polysaccharides and mainly composed of residual lignin, which can easily collapse during drying and needs specific consolidation treatments. For this reason, the chemical characterization of archaeological lignin is of primary importance in the diagnosis and conservation of waterlogged wood artifacts. Current knowledge of the lignin degradation processes in historical and archaeological wood is extremely inadequate. In this study lignin extracted from archaeological waterlogged wood was examined using both Py-GC/MS, NMR spectroscopy and GPC analysis. The samples were collected from the Site of the Ancient Ships of San Rossore (Pisa, Italy), where since 1998 31 shipwrecks, dating from 2nd century BC to 5th century AD, have been discovered. The results, integrated by GPC analysis, highlight the depolymerization of lignin with cleavage of ether bonds, leading to an higher amount of free phenol units in the lignin from archaeological waterlogged wood, compared to sound lignin from reference wood of the same species.

A GC-MS study on the deterioration of lipidic paint binders

Abstract This paper presents a study on the degradation of lipidic paint binders induced by irradiation with UV light (365 nm), exposure to urban air pollutants such as NOx and SO2 and combinations of the various treatments. The characterisation of lipidic binders has been performed by a GC-MS procedure on a series of non-pigmented paint specimens prepared at the Opificio delle Pietre Dure–Firenze (Italy) and submitted to accelerated ageing. The results show that UV irradiation and exposure to NOx and SO2 increased the polymerisation and cross-linking of the paint thus facilitating the cleavage of fatty acid chains as a result of progressed oxidation up to the formation of oxalic acid. The presence of oxalic, malonic, succinic, glutaric, adipic, pimelic, OH-octadecenoic acids and cholestenes describes the behaviour of aged paint layers. In samples of paintings by Cimabue, Raffaello and Boucher, oxalic acid and oxidised carboxylic acids have been found, confirming the results obtained in the paint specimens.

Integrated analytical techniques for the study of ancient Greek polychromy.

The materials used in the decoration of three painted astragaloi (knucklebones) from the Koroneia cave (Greece) were investigated by means of sequential application of non-destructive and destructive techniques: optical microscopy, environmental scanning electron microscopy coupled with X-ray microanalysis (ESEM-EDX), Fourier transform infrared spectroscopy (FTIR) with micro-attenuated total reflection (mu-ATR) technique, high performance liquid chromatography (HPLC) coupled with UV-fluorescence and gas chromatography-mass spectrometry (GC-MS) were used. The main results highlighted that the three astragaloi were prepared with a ground of ochre or iron clay and painted with a proteinaceous matter such as binder egg tempera. Both FTIR and GC-MS agree in the detection of lipids that can be related to egg. Organic dyestuffs identified as madder lake and shellfish purple were used together with inorganic pigments.