Identification of proteinaceous binders in paintings: A targeted proteomic approach for cultural heritage

Abstract Identification of proteins in paintings and polychrome objects is a challenge, which requires the development of tailored analytical approaches. In the present study, a targeted proteomics approach was developed for discriminating among the three most common proteinaceous materials used as paint binders, i.e. milk, egg, and animal glue. In this study a specific database of peptides was created based on tandem MS analyses of tryptic digests of several paint samples collected from a variety of art objects of different ages and conservation conditions. Specific peptide markers of each protein were then selected and monitored by LC-MSMS in Multiple Reaction Monitoring (MRM) ion mode, together with their specific precursor ion-product ion transitions, as defined by their unique amino acid sequence. The developed method enabled a sensitive and reliable detection of the target peptides in a selection of case studies, leading to the unambiguous identification of the proteins used as paint binders. The method showed greatly increased sensitivity compared to currently available strategies

An Insight into Gandharan Art: Materials and Techniques of Polychrome Decoration

Gandharan art developed in the Himalayan area in the early centuries CE. It has been investigated mostly from an iconographic point of view, missing, until very recently, a systematic technical investigation of materials and techniques. Recently our team began performing chemical analyses of the traces of the polychromy originally covering statues, reliefs and architectural decorations, to discover the ancient painting techniques and artistic technologies. This paper presents the results of the analytical investigation (optical microscopy, Raman spectroscopy and gas chromatography coupled with mass spectrometry) of pigments, ground layers and binders of a new group of samples taken from stucco architectural decorations (2nd–3rd/4th centuries CE). The samples were collected directly at an archaeological site in the Swat Valley, ensuring the exact knowledge of their stratigraphic provenance, as well as the absence of any restoration treatment applied prior sampling. The results are discussed in the wider context of Gandharan polychromy investigated so far by our team, as found in sculptures and architectural decorations preserved in museums (in Italy and France) and in archaeological excavations in Pakistan. The aim of this research is to shed light on the materials and techniques of this Buddhist ancient art from this region and on the influences exerted on it from Eastern and Western artistic traditions

Evaluating cleaning systems for use on water sensitive modern oil paints: a comparative study

This paper outlines the approach and key findings of systematic studies into the use of various surface cleaning materials on a range of accelerated-aged sensitive oil paint surfaces, carried out through the Cleaning Modern Oil Paints (CMOP) project. Studies involved the use of recently introduced options such as adjusted pH and conductivity waters, spreadable gels, rigid gels, silicone emulsifiers, and mineral spirits-based microemulsions, with additional explorations into the effects of application methods. The evaluation methodology encompassed star diagrams designed to capture observations made during cleaning tests, and paint surface evaluations using digital microscopy, colour and gloss assessment, and ATR-FTIR analysis. In most cases, the most promising free solvents were subsequently incorporated into spreadable and rigid gels, water-in-oil microemulsions and silicone emulsions, tailoring the approach to further minimise undesirable effects where possible. Cleaning system residues were also investigated using visual inspection, microscopy and ATR-FTIR analysis, with a selection of samples further investigated using a pyrolysis on-line micro-reaction sampler and XPS analysis. The combined results offer information on the advantages and risks associated with each cleaning material, and an approach to optimising wet systems for the cleaning of sensitive oil painted surfaces

The evolution of the materials used in the yun technique for the decoration of Burmese objects: lacquer, binding media and pigments

Abstract A series of Burmese lacquered objects decorated with the yun (incised) technique and belonging to the British Museum’s collection was analysed with the aim to investigate the decorative materials—lacquer, binding media, additives and pigments—used in the production of these objects, which span chronologically from the eighteenth century to the late twentieth century. As the manufacturing process is supposed to have remained very similar over this time period, especially regarding the use of materials, we were interested in scientifically assessing for the first time the nature of these materials and the correspondence to the written sources in the relation to their specific use. Gas chromatography mass spectrometry (GC–MS) and analytical pyrolysis with in situ silylation coupled with GC–MS (Py(HMDS)GC–MS) were used for the identification of the organic components in several samples taken from the coloured areas of the objects. Fibre optic reflectance (FORS) and Raman spectroscopies were used to identify the pigments after a visual investigation of the samples by digital microscopy. Burmese lacquer was detected in all objects and trends in its degradation were highlighted. Lipids, proteins and saccharide material were found to be mixed with lacquer, and they appeared to be applied with specific pigments, in good agreement with the written records, apart from proteins, which are not mentioned. The use of synthetic pigments, such as phthalocyanines blue and green and chrome yellow, was assessed in the most recent objects, showing an evolution in the use of pigments. Indigo, although expected, was not identified in any of the green samples and Prussian blue appeared to be the main source of blue colour. All this information is of fundamental importance for conservation practices and corrects the general opinion about the production materials of these objects. These results also open the way to future research dedicated to exploring the chemical interaction between Burmese lacquer, proteins, lipids, gums and pigments, with the aim to predict possible differences in degradation pathways

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

Abstract Background Saccharide 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. Results This 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. Conclusions The 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.</p

The chemistry of pastels: Investigation of the organic materials in a drawing by Umberto Boccioni

Although many prominent artists have experimented with pastels, this technique has been the subject of very limited scientific research. The first known recipes of pastels date back to the 16th century, but only during the 18th century did the pastel technique become more common. Identifying and characterising the organic constituents in pastels materials is challenging given that they are present in extremely low concentrations and could be produced using many organic substances, whose chemical composition alters during ageing. The chemical-physical behaviour of organic media in artworks is often crucial in causing the degradation problems, which need to be addressed by conservation. We evaluated the applicability of an analytical approach based on chromatography and mass spectrometry to investigate the composition of the pastels used by Umberto Boccioni in a drawing dated 1908 and conserved at the Museo del Novecento in Milan (Italy). The investigation of the formulation of artists’ pastels used in the first decade of the 20th century is particularly important in order to improve the knowledge of this technique. The analysis highlighted the presence of proteins and plant gums in the artwork samples, with differences in the composition for the different samples

A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Method for the Identification of Anthraquinones: the Case of Historical Lakes

This study deals with the identification of anthraquinoid molecular markers in standard dyes, reference lakes, and paint model systems using a micro-invasive and nondestructive technique such as matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry (MALDI-ToF-MS). Red anthraquinoid lakes, such as madder lake, carmine lake, and Indian lac, have been the most widely used for painting purposes since ancient times. From an analytical point of view, identifying lakes in paint samples is challenging and developing methods that maximize the information achievable minimizing the amount of sample needed is of paramount importance. The employed method was tested on less than 0.5 mg of reference samples and required a minimal sample preparation, entailing a hydrofluoric acid extraction. The method is fast and versatile because of the possibility to re-analyze the same sample (once it has been spotted on the steel plate), testing both positive and negative modes in a few minutes. The MALDI mass spectra collected in the two analysis modes were studied and compared with LDI and simulated mass spectra in order to highlight the peculiar behavior of the anthraquinones in the MALDI process. Both ionization modes were assessed for each species. The effect of the different paint binders on dye identification was also evaluated through the analyses of paint model systems. In the end, the method was successful in detecting madder lake in archeological samples from Greek wall paintings and on an Italian funerary clay vessel, demonstrating its capabilities to identify dyes in small amount of highly degraded samples