Background: Illuminated manuscripts are complex multi-layer and multi-material objects. To this difficulty, from the analytical point of view, is added the impossibility of removing samples from these paintings for the study of their materials and techniques. There are relatively few analytical methods that satisfy these constraints as the availability of non-invasive techniques adapted to painted manuscripts is limited and mainly focused on the characterization of inorganic compounds. In the context of a research project on the analytical study of the forty miniatures in the Marcadé collection (Treasury of the Saint-André Cathedral of Bordeaux, XIII to XVI century), the potential of two non-invasive methods, hyperspectral imaging (HSI) and spectrofluorimetry is explored. Results: The methodological development of these techniques as well as preliminary tests on miniatures recreated according to medieval recipes and materials, allowed the validation of the analytical parameters and the creation of a database of reference spectra (parchments, pigments, binders). Hyperspectral imaging associates reflectance spectra with each pixel of the image and treats the signal received in various wavelengths. The characteristics of the spectral signal in VIS range or NIR are used to get an identification and a localization of the components. It allows the study of the entire image and offers lots of ways to work: comparison of spectra, mapping, principal component analyses and false color images. Spectrofluorimetry is a sensitive method which gives information on fluorescent organic compounds under UV or visible light. Emission and excitation spectra of five red pigments in binding media have been collected. These methods were compared with X-ray fluorescence spectrometry for the qualitative analysis and mapping of the inorganic elements in a facsimile which had been purposely reproduced by an illumination painter who worked with original medieval recipes for the sake of developing the present study. Conclusions: The combination of all these techniques allows good identification of all the materials used on an illuminated manuscript. The pertinent selection of the wavelengths used with the HSI system and a preliminary database and study of materials under UV and white light is described in this paper.
Blue colors were sparsely used in the first colored Japanese ukiyo-e prints but became predominant during the 19th century, mainly due to the integration of the synthetic Prussian blue in the palette of the printers around 1830. For a long time, researchers have assumed that the traditional Japanese organic blue colorants such as indigo were substituted by cheaper Prussian blue. Some analytical studies conducted on such artworks showed evidence of the common use of indigo and Prussian blue in Japanese paintings, alone or mixed together. Recent measurements carried out on bluish areas of an ukiyo-e designed by Utamaro showed the simultaneous use of the two pigments. However, if visible reflectance spectroscopy suggested the single use of Indigo, Fourier transform infrared spectroscopy (FTIR) also indicated the presence of Prussian blue.These results question about the possible identification of all the pigments of a colored mixture by using a single analytical technique. Without using FTIR spectroscopy, the Prussian blue would not have been detected, whereas on infrared spectra the expected specific bands ascribed to indigo are not identified. The objective of this work is to investigate mixtures of pigments, using noninvasive spectroscopic techniques in order to assess their limits of detection. Fluorimetry, hyperspectral imaging, and infrared spectroscopies have been performed on three color charts made of indigo, Prussian blue, and mixtures of them at different proportions of matter. The results emphasize the systematic identification of Prussian blue thanks to infrared spectroscopy, whereas the identification of indigo, mixed with Prussian blue, appears to be more challenging. K E Y W O R D Sblue pigments, fluorescence, hyperspectral imaging, infrared spectroscopies, Japanese ukiyo-e prints
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