Identification of pigments in modern and contemporary arts is indispensable to determine correct conservation strategies, to study degradation processes and to answer authenticity‐related questions. Since the early 20th century, the introduction of synthetic organic pigments (SOPs) has enormously increased the number of available pigments. Micro‐Raman spectroscopy has proven to be the first line technique for the identification of these pigments, which often only show small variations on the same basic chemical structures. To ensure a correct identification, however, an as complete as possible library of reference spectra is needed. Although reference spectra of SOPs have been published before, they have always been limited to a certain number of pigments. Some publications discuss only one or a few chemical classes, and others are limited to a certain number of pigments belonging to different classes; none, however, have attempted to create an extensive library of commercially available pigments. Moreover, most of the reference spectra published so far are only available as small imprints or as peak lists and, as such, hardly usable for spectral matching algorithms. Often, flow charts have been developed on the basis of the pigments studied, to help in identifying unknown SOPs. In this paper, a digital spectral library that comprehends almost 300 spectra of different SOPs is presented. The library was tested by means of non‐invasive analysis of four contemporary paintings from the collections of the Stedelijk Museum voor Actuele Kunst (Ghent, Belgium). Published flow charts have been evaluated in relation to digital search algorithms by using the extensive library of SOPs. To enable fellow research and conservation institutes to make use of these data, the nearly 300 reference spectra of synthetic organic pigments are available in digital format on http://modern.kikirpa.be. Copyright © 2012 John Wiley & Sons, Ltd.

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Comprehension of the materials, such as binding media, used by artists is of uttermost importance in restoration and in art historical studies. The most frequently used binders are drying oils and proteins; in this study focus is placed on proteins. Most actual methods for protein binder identification are based on complete hydrolyzation of the protein matter into its amino acids and separation/detection with gas chromatographymass spectrometry (GC-MS) or high performance liquid chromatography (HPLC) after derivatization. Because amino acids itself are not characteristic for a protein, identification is often based on the relative amount of 7 stable amino acids. In the current study a proteomics approach was used, in which the proteins were digested enzymatically into peptides using trypsin before being separated and detected by liquid chromatography -electronspray ionisation tandem mass spectrometry (LC-ESI-MS/MS). Mascot (Matrix Science) was used to analyze the resulting data and for protein identification. This way, amino acid sequences could be studied that retain much more information about the proteins, their degradation and pigment-binder interactions. The protein content of homemade paint samples was extracted using different methods and analysed to select the best extraction strategy based on the number of peptides that were identified. A large dataset of 4 binders (animal glue, egg yolk, egg white and casein), mixed with 10 common pigments with different chemical properties was used to study the influence of pigments on the extraction method.Analytical characteristics of the selected method were determined. Finally the method was applied to historic paint samples. The results were compared with those obtained by traditional amino acid analysis methods.

Proteomics techniques are increasingly applied for the identification of protein binders in historical paints. The complex nature of paint samples, with different kinds of pigments mixed into, and degradation by long term exposure to light, humidity and temperature variations, requires solid analysis and interpretation methods. In this study matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectra of tryptic-digested paint replicas are subjected to principal component analysis (PCA) and soft independent modelling of class analogy (SIMCA) in order to distinguish proteinaceous binders based on animal glues, egg white, egg yolk and milk casein from each other. The most meaningful peptide peaks for a given protein class will be determined, and if possible, annotated with their corresponding amino acid sequence. The methodology was subsequently applied on egg temperas, as well as on animal glues from different species. In the latter small differences in the MALDI-TOF mass spectra can allow the determination of a mammal or sturgeon origin of the glue. Finally, paint samples from the 16(th) century altarpiece of St Margaret of Antioch (Mlynica, Slovakia) were analysed. Several expected peaks are either present in lower abundance or completely missing in these natural aged paints, due to degradation of the paints. In spite of this mammalian glue was identified in the St Margaret samples.

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