Application of matrix-assisted laser desorption and ionization time of flight mass spectrometry to the study of the proteinaceous binders in paint: blue paint composition in the series "The Life of Virgin" by Alonso Cano (17th century) as a case study.

The identification of proteinaceous materials in paint constituents provides very valuable information regarding the techniques used by the painter and the most suitable procedures for conserving and restoring their works. Although the analysis of proteinaceous materials is nowadays a common task when dealing with works of art, the reliable detection and identification of protein traces is still complicated, particularly when very small samples can be taken that may contain a mixture of different organic materials (oils, waxes, resins, gums etc.). We therefore proposed a proteomic approach to investigate protein materials in paintings at trace levels in order to obtain a better understanding of the painter's technique. After trypsin digestion of the paint samples, mass spectra were obtained by matrix-assisted laser desorption and ionization time of flight mass spectrometry (MALDI-TOF-MS) and they were compared with the Mascot database and with theoretical digested proteins. This study contributes to the knowledge about the technique used by Alonso Cano (Granada, Spain, 1601-1667), one of the most original and brilliant artists from the Spanish Golden Age (17th century), in the series called the Life of the Virgin (six paintings), part of the iconographic program about the life of the Virgin Mary, nowadays seen in the main chapel of Granada Cathedral. The objective of the present study was to test the use of proteinaceous material, mainly egg yolk, in the paint used by Cano, as suggested in previous research, although this would have been unusual at that time when most artists used oil paints. Based on the results of the analysis here presented, the use of protein in the binding media can most likely be excluded.

Compositional and quantitative microtextural characterization of historic paintings by micro-X-ray diffraction and Raman microscopy.

This work shows the benefits of characterizing historic paintings via compositional and microtextural data from micro-X-ray diffraction (µ-XRD) combined with molecular information acquired with Raman microscopy (RM) along depth profiles in paint stratigraphies. The novel approach was applied to identify inorganic and organic components from paintings placed at the 14th century Islamic University-Madrasah Yusufiyya-in Granada (Spain), the only Islamic University still standing from the time of Al-Andalus (Islamic Spain). The use of µ-XRD to obtain quantitative microtextural information of crystalline phases provided by two-dimensional diffraction patterns to recognize pigments nature and manufacture, and decay processes in complex paint cross sections, has not been reported yet. A simple Nasrid (14th century) palette made of gypsum, vermilion, and azurite mixed with glue was identified in polychromed stuccos. Here also a Christian intervention was found via the use of smalt, barite, hematite, Brunswick green and gold; oil was the binding media employed. On mural paintings and wood ceilings, more complex palettes dated to the 19th century were found, made of gypsum, anhydrite, barite, dolomite, calcite, lead white, hematite, minium, synthetic ultramarine blue, and black carbon. The identified binders were glue, egg yolk, and oil.

Innovative analytical methodology combining micro-x-ray diffraction, scanning electron microscopy-based mineral maps, and diffuse reflectance infrared fourier transform spectroscopy to characterize archeological artifacts.

Excavations at the 14th century Moorish rampart (Granada, Spain) unearthed a brick oven alongside black ash and bone stratigraphic layers. In situ evidence suggests the oven served to fabricate a wall coating including powdered burnt bones. Original ad hoc analyses improved on conventional methods were used to confirm this hypothesis. These methods enable (i) nondestructive micro-X-ray diffraction (mu-XRD) for fast mineralogical data acquisition (approximately 10 s) and moderately high spatial (approximately 500 microm) resolution and (ii) identification and imaging of crystalline components in sample cross-sections via mineral maps, yielding outstanding visualization of grain distribution and morphology in composite samples based on scanning electron microscopy-energy dispersion X-ray spectrometry (SEM-EDX) elemental maps. Benefits are shown for applying diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) vs transmittance-FT-IR (T-FT-IR) to analyze organic and inorganic components in single samples. Complementary techniques to fully characterize artifacts were gas chromatography/mass spectroscopy (GC/MS), optical microscopy (OM), conventional powder XRD, and (14)C dating. Bone-hydroxyapatite was detected in the coating. Mineralogical transformations in the bricks indicate oven temperatures well above 1000 degrees C, supporting the hypothesis.

Collagen-based proteinaceous binder-pigment interaction study under UV ageing conditions by MALDI-TOF-MS and principal component analysis.

This study focuses on acquiring information on the degradation process of proteinaceous binders due to ultra violet (UV) radiation and possible interactions owing to the presence of historical mineral pigments. With this aim, three different paint model samples were prepared according to medieval recipes, using rabbit glue as proteinaceus binders. One of these model samples contained only the binder, and the other two were prepared by mixing each of the pigments (cinnabar or azurite) with the binder (glue tempera model samples). The model samples were studied by applying Principal Component Analysis (PCA) to their mass spectra obtained with Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS). The complementary use of Fourier Transform Infrared Spectroscopy to study conformational changes of secondary structure of the proteinaceous binder is also proposed. Ageing effects on the model samples after up to 3000 h of UV irradiation were periodically analyzed by the proposed approach. PCA on MS data proved capable of identifying significant changes in the model samples, and the results suggested different aging behavior based on the pigment present. This research represents the first attempt to use this approach (PCA on MALDI-TOF-MS data) in the field of Cultural Heritage and demonstrates the potential benefits in the study of proteinaceous artistic materials for purposes of conservation and restoration.

Benefits of applying combined diffuse reflectance FTIR spectroscopy and principal component analysis for the study of blue tempera historical painting.

This paper explores the application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to the examination of historic blue pigments and blue tempera paintings commonly found on works of art. The discussion is mainly focused on the practical benefits of using this technique joined to principal component analysis (PCA), a powerful multivariate analysis tool. Thanks to the study of several replica samples that contain either pure blue pigments (azurite, lapis lazuli and smalt), or pure binder (rabbit glue) and mixtures of each of the pigments with the binder (tempera samples), different aspects of these benefits are highlighted. Comparative results of direct spectra and multivariate analysis using transmittance-Fourier transform infrared spectroscopy (T-FTIR) are discussed throughout this study. Results showed an excellent ability of PCA on DRIFT spectra for discriminating replica samples according to differing composition. Several IR regions were tested with this aim; the fingerprint IR region exhibited the best ability for successfully clustering the samples. The presence of the binder was also discriminated. Only using this approach it was possible to completely separate all the studied replica samples. This demonstrates the potential benefits of this approach in identifying historical pigments and binders for conservation and restoration purposes in the field of Cultural Heritage.