In this project, micro-Raman (µ-Raman) spectroscopy has been used as a means to investigate the pigments employed in decoration of Anasazi pottery. Analysis of Raman spectra revealed the presence of organic-(amorphous carbon), iron-and/or manganese-based pigments in line with the known pictorial materials used by Anasazi people. The results were also complemented by studies employing a scanning electron microscope equipped with a microanalysis energy dispersive X-ray detection (SEM/EDX) system, which proved helpful mainly while identifying the manganese-based minerals (i.e. pyrolusite). Knowledge of the pigments augments our understanding of the materials favored by the different production centers and of the artistic skills of ceramic producers.
Here, the photo-oxidative degradation of several terpenoid varnishes usually encountered in conservation of cultural heritage has been investigated. Samples were prepared by dissolving dammar, mastic, colophony, sandarac and bleached shellac in suitable solvents or by heating mastic, colophony, sandarac and Manila copal with linseed oil. The alteration effects of this broad set of samples induced by light exposure in an ageing chamber, were thoroughly characterized using transmission FTIR spectroscopy, colorimetry, and gravimetric measurements. The various varnishes exhibited a similar saturating photo-oxidative kinetics upon the exposure time but significant quantitative differences were pointed out. A decreasing of the methyl and methylene stretching bands was observed for both solvent and oil based varnishes, which suggests the alteration effects begin with hydrogen atom abstractions. The consequent reaction with oxygen, catalyzed by irradiation and temperature rise lead to the increase of carbonyl and hydroxyl functionalities, thus suggesting the formation of new compounds containing carboxylic, ketone and ester groups and lactonised structures. At the same time, cross-linking and extensive polymerization were clearly observed for sandarac and shellac solvent varnishes. Measurement and comparison of the photo-oxidative and discoloration effects of the present set of samples, provide a general picture of the ageing phenomenology of the natural varnishes, which can be usefully exploited in characterization and conservation of easel paintings and other artworks.
A concise insight into the outputs provided by the latest prototype of visible-near infrared (Vis-NIR) multispectral scanner (National Research Council-National Institute of Optics, CNR-INO, Italy) is presented. The analytical data acquired on an oil painting Madonna of the Rabbit by É. Manet are described. In this work, the Vis-NIR was complemented with X-ray fluorescence (XRF) mapping for the chemical and spatial characterization of several pigments. The spatially registered Vis-NIR data facilitated their processing by spectral correlation mapping (SCM) and artificial neural network (ANN) algorithm, respectively, for pigment mapping and improved visibility of pentimenti and of underdrawing style. The data provided several key elements for the comparison with a homonymous original work by Titian studied within the ARCHive LABoratory (ARCHLAB) transnational access project.
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