Multifocus HDR VIS/NIR hyperspectral imaging and its application to works of art.

This paper presents a complete framework for capturing and processing hyperspectral reflectance images of artworks in situ, using a hyperspectral line scanner. These capturing systems are commonly used in laboratory conditions synchronized with scanning stages specifically designed for planar surfaces. However, when the intended application domain does not allow for image capture in these controlled conditions, achieving useful spectral reflectance image data can be a very challenging task (due to uncontrolled illumination, high-dynamic range (HDR) conditions in the scene, and the influence of chromatic aberration on the image quality, among other factors). We show, for the first time, all the necessary steps in the image capturing and post-processing in order to obtain high-quality HDR-based reflectance in the visible and near infrared, directly from the data captured by using a hyperspectral line scanner coupled to a rotating tripod. Our results show that the proposed method outperforms the normal capturing process in terms of dynamic range, color and spectral accuracy. To demonstrate the potential interest of this processing strategy for on-site analysis of artworks, we applied it to the study of a vintage copy of the famous painting "Transfiguration" by Raphael, as well as a facsimile of "The Golden Haggadah" from the British Library of London. The second piece has been studied for the identification of highly reflective gold-foil covered areas.

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.

Revisitation of the phenylisothiocyanate-derivatives procedure for amino acid determination by HPLC-UV.

A revisitation of the well known chromatographic procedure for the determination of amino acids as phenylthiocarbamyl derivatives (PTC) is performed. The method was developed for a microbore column that it is more appropriate to our later aims, the characterization of proteinaceous binders present in microsamples coming from the Cultural Heritage field. Several variables relating to chromatographic aspects were studied such as the pH and temperature of the mobile phase, buffer and modifier (triethylamine) concentrations in mobile phase and the stability of PTC-derivatives in solution. The calibration function was studied in depth. To prevent the heteroscedastic behaviour that it is observed, we used the weighed least squares fitting as the best strategy among other normalizing transformations, such as square root and logarithmic functions. Finally, the proposed method showed results similar to the traditional method in terms of efficiency, runtime, LODs and other characteristics, but with two additional advantages: a lower mobile phase consumption and the possibility of working with a lower sample volume. The usefulness of proposed method is checked against easel painting samples of Pictorial Heritage.

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.