Molecular Tracing of the Biological Origin of Drying Oils Used in Works of Art (original) (raw)
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Tracing the biological origin of animal glues used in paintings through mitochondrial DNA analysis
Analytical and Bioanalytical Chemistry, 2011
We report the development of a suitable protocol for the identification of the biological origin of binding media on tiny samples from ancient paintings, by exploitation of the high specificity and high sensitivity offered by the state-of-the art DNA analysis. In particular, our aim was to molecularly characterize mitochondrial regions of the animal species traditionally employed for obtaining glues. The model has been developed using aged painting models and then tested to analyze the organic components in samples from the polychrome terracotta Madonna of Citerna by Donatello (1415–1420), where, by GC–MS and FTIR spectroscopy, animal glues and siccative oils were identified. The results obtained are good in terms of both sensibility and specificity of the method. First of all, it was possible to confirm that Donatello used animal glue for the preparation of the painted layers of the Madonna of Citerna and, specifically, glue derived from Bos taurus. Data obtained from sequencing confirm that each sample contains animal glue, revealing that it was mostly prepared from two common European taurine lineages called T2 and T3. There is one remarkable exception represented by one sample which falls into a surviving lineage of the now extinct European aurochs. Figure One of the four microscale samples of the “Madonna of Citerna” collected during restoration (upper) and amplicons obtained using primers specific for cattle, swine, rabbit and sheep on DNA isolated from the 4 microscale samples (S1, S2, S3 and S4)
Gas chromatography/mass spectrometry of oils and oil binders in paintings
Journal of Separation Science, 2008
Gas chromatography/mass spectrometry of oils and oil binders in paintings A GC/MS procedure has been developed, optimized, and applied to characterization of oil binders in paintings. The procedure involves hydrolysis of lipids to fatty acids (FAs) and derivatization of FAs to fatty acid methyl esters (FAMEs) by a solution of sodium methanolate in methanol at an elevated temperature. FAMEs are analyzed by temperature-programed GC followed by full-scan MS. Old and dried samples are subjected to extraction of nonpolymerized FAMEs into dichloromethane prior to hydrolysis. The method provides a good repeatability of results and has been applied to the characterization of common plant oils used in paintings, to commercial oil and tempera paints, to model painting samples, and to samples taken from real paintings. The fresh oils and binders can readily be identified and characterized. The ratio of the methyl esters of palmitic and stearic acids can be used to characterize oil binders in old works of art.
Conservation Issues of Modern Oil Paintings: A Molecular Model on Paint Curing
Accounts of Chemical Research, 2019
20th-and 21st-century oil paintings are presenting a range of challenging conservation problems that can be distinctly different from those noted in paintings from previous centuries. These include the formation of vulnerable surface 'skins' of medium and exudates on paint surfaces, efflorescence, unpredictable water and solvent sensitivity and incidence of paint dripping which can occur within a few years after the paintings were completed. Physicochemical studies of modern oil paints and paintings in recent years have identified a range of possible causal factors for the noted sensitivity of painting surfaces to water and protic solvents, including the formation of water-soluble inorganic salts and/or the accumulation of diacids at the paint surface, which are oxidation products of the oil binder. Other studies have investigated the relationship between water sensitivity and the degree of hydrolysis of the binder, the proportions of free fatty and dicarboxylic acids formed, as well as the relative content of free metal soaps. Thus far, data indicate that the qualitative and quantitative composition of the non-polymerised fractions of the oil binder cannot be solely or directly related to the solvent sensitivity of the paint film. Conclusions therefore indicate that the polymeric network, formed upon the curing of the oil plays a fundamental role; suggesting that water sensitivity-at least in some cases-may be related to the poor development, and/or polar nature of the formed polymeric network rather than the composition of the non-polymerised fractions. Poorly developed polymeric networks, in combination with the migration of polar fractions i.e. dicarboxylic and hydroxylated fatty acids towards the paint surface, can be related to other degradation phenomena, including the separation and migration of the paint binder which can lead to the presence of observable skins of medium, as well as the more alarming phenomenon of liquefying or dripping oil paints. It is thus crucial to understand the molecular composition of these Among the issues encountered, water sensitivity is proving particularly challenging, as the removal of accumulated, deposited soiling, often known as surface cleaning, traditionally relies upon water as the key component. In these cases, water may not be safely applied without causing undesirable surface disruption and pigment pickup 3-7. Water sensitivity has now been identified in model oil paint samples prepared from raw materials 4,8,9 , in samples taken from batches of manufactured paint 10 , and in several paintings 9-13. Sensitivity may be limited to certain colours, may affect the whole surface of a painting, may be specific to some paint brands or lines, and may affect specific pigments across several brands 8,10,13. Recent research has identified some of the causes and/or contributing factors relating to the changes observed in modern oils (i.e. water sensitivity and poor drying behaviour) including: the conversion of magnesium carbonate filler material used in some artists' paints to water-soluble magnesium sulphate heptahydrate salts at paint surfaces 4 (Figure 2), the migration of polar diacids to oil paint surfaces 6 , and in some cases, the use of semi-or non-drying oils such as safflower 14,15 or palm oil 16 as the binder or proportion of the binder. University of Pisa. Her research focuses on the development and optimisation of sample preparation methods and analytical procedures to study the interaction and distribution of organic and inorganic compounds in microsamples from cultural heritage.
Pitfalls in drying oils identification in art objects by gas chromatography
Journal of Separation Science, 2006
Drying oils identification in art objects is an important step in the scientific investigation of the artifact which provides conservators and art historians with valuable information concerning materials used and painting techniques applied. The present communication is devoted to pitfalls and troubleshooting in drying oils identification by means of GC-MS analysis of fatty acids composition in a microsample of an art object. We demonstrate that in the case of nonlinear instrument response the ratios of palmitic to stearic (P/S), distinctive for each oil type and used for drying oil identification, depend on sample dilution so that different dilutions of the same sample can give different P/S ratios. This phenomenon can hinder drying oil identification and lead to erroneous interpretations. This is an important observation as nowadays very often the P/S ratio is calculated from the corresponding peak area ratios or by the use of one-point calibration method. In these approaches, the linearity of the instrument response is not controlled and ensured. In the case analyzed, the nonlinear instrument response was attributed to incomplete sample evaporation in the injector. Packing of the glass liner with deactivated glass wool improved the sample evaporation and ensured the linearity of the instrument response and independence of the P/S ratio from sample dilution.
Talanta, 2011
The correct identification of drying oils plays an essential role in providing an understanding of the conservation and deterioration of artistic materials in works of art. To this end, this work proposes the use of peak area ratios from fatty acids after ensuring that the linear responses of the detector are tested. A GC-MS method, previously reported in the literature, was revisited to its developed and validated in order to identify and quantify of eight fatty acids that are widely used as markers for drying oils in paintings, namely myristic acid (C 14:0), palmitic acid (C 16:0), stearic acid (C 18:0), oleic acid (C 18:1), linoleic acid (C 18:2), suberic acid (2C 8), azelaic acid, (2C 9) and sebacic acid (2C 10). The quaternary ammonium reagent m-(trifluoromethyl)phenyltrimethylammonium hydroxide (TMTFAH) was used for derivatization prior to GC-MS analysis of the oils. MS spectra were obtained for each methyl ester derivative of the fatty acids and the characteristic fragments were identified. The method was validated in terms of calibration functions, detection and quantification limits and reproducibility using the signal recorded in SIR mode, since two of the methyl derivatives were not totally separated in the chromatographic run. The proposed method was successfully applied to identify and characterise the most widely used drying oils (linseed oil, poppy seed oil and walnut oil) in the painting La Encarnación. This 17th century easel painting is located in the main chapel of the cathedral in Granada (Spain) and was painted by the well-known artist of the Spanish Golden Age, Alonso Cano (1601-1667).
Scientific Reports
Undertaking the conservation of artworks informed by the results of molecular analyses has gained growing importance over the last decades, and today it can take advantage of state-of-the-art analytical techniques, such as mass spectrometry-based proteomics. Protein-based binders are among the most common organic materials used in artworks, having been used in their production for centuries. However, the applications of proteomics to these materials are still limited. In this work, a palaeoproteomic workflow was successfully tested on paint reconstructions, and subsequently applied to micro-samples from a 15th-century panel painting, attributed to the workshop of Sandro Botticelli. This method allowed the confident identification of the protein-based binders and their biological origin, as well as the discrimination of the binder used in the ground and paint layers of the painting. These results show that the approach is accurate, highly sensitive, and broadly applicable in the cult...
Analytical and Bioanalytical Chemistry, 2014
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The stability of paintings and the molecular structure of the oil paint polymeric network
Scientific Reports, 2021
A molecular-level understanding of the structure of the polymeric network formed upon the curing of air-drying artists' oil paints still represents a challenge. In this study we used a set of analytical methodologies classically employed for the characterisation of a paint film-based on infrared spectroscopy and mass spectrometry-in combination with solid state NMR (SSNMR), to characterise model paint layers which present different behaviours towards surface cleaning with water, a commonly applied procedure in art conservation. The study demonstrates, with the fundamental contribution of SSNMR, a relationship between the painting stability and the chemical structure of the polymeric network. In particular, it is demonstrated for the first time that a low degree of cross-linking in combination with a high degree of oxidation of the polymeric network render the oil paint layer sensitive to water. The curing of a drying oil-a glycerolipid based on polyunsaturated fatty acids-involves autoxidative radical chain reactions, which are light initiated, and metal catalysed 1-6. Upon curing, fatty acids in triglycerides undergo several transformations, which entail the formation of epoxy, hydroxyl, oxo and carbonyl moieties, as well as new CC and CO -C bonds 1,4,6,7. Small oxidised molecules are formed by oxidative degradation of the fatty acid chains upon evolution of peroxyl and alkoxyl moieties 4,6 , and are quickly lost by evaporation 8. With time, hydrolysis of ester bond takes place 9-11 and, depending on the nature of the pigment and additives, formation of metal soaps occurs 12. As a result, the organic molecular composition of an oil paint layer evolves from polyunsaturated triglycerides to a significantly more complex system, whose composition evolves over years, even centuries, entailing the simultaneous presence of free fatty acids, free dicarboxylic acids, mono-, di-and triglycerides, and cross-linked fractions 2,3,5,7,10,11,13-17. In addition, when metal soaps are formed, carboxyl moieties are bound to metal cations, in variable proportions depending on the age of the paint, the environmental conditions 18,19 , and the nature of the pigment 20 , leading to the formation of free metal soaps and ionomer-like networks 21-23. The detection of a drying oil in a painting is, in general, relatively straightforward, and can be achieved using a variety of analytical approaches, including, most commonly, those based on FTIR 24-26 , GC-MS 27 , Py-GC-MS 28 , HPLC-MS 29. On the other hand, the chemical speciation of the different fractions in a painting sample requires different analytical approaches. Free acidic moieties are detected by IR spectroscopy 30. Free fatty and dicarboxylic acids can be determined qualitatively and quantitatively by GC-MS based techniques 11,13,31,32 , HPLC-MS 14 and flow injection analysis coupled with ESI-MS 33. Metal soaps have been extensively studied with spectroscopic techniques which are helping to distinguish between free metal soaps and those belonging to the ionomeric network 12,20,21,23,30,34-40. Free metal soaps may also be determined by using mass spectrometry 32,41. HPLC-MS based methods are the methods of choice for glyceride profiling in paintings 29 , and flow injection analysis coupled with ESI-MS can help visualise the distribution of glycerides and more abundant oligomers in a paint layer 33,42. While spectroscopic techniques allow the bulk of the sample or its surface to be analysed, based on the instrumental setup used, GC-MS, HPLC-MS and ESI-MS give only information on the soluble/hydrolysable fraction of the oil matrix. Characterisation of the cross-linked fractions is significantly more challenging, if possible at all. Fatty and dicarboxylic acids covalently bound to the polymeric network through ester bonds can be analysed by GC-MS after hydrolysis, which can be achieved both in acidic and alkaline environments 27,28. Analytical pyrolysis is the