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Couleur de la matière picturale : caractérisation des pigments et des mélanges de pigments, effets induits par l'adjonction de liant et de charges

Abstract : Diffuse reflectance spectroscopy in the visible range is surprisingly an analytical technique rarely performed to identify the components of pictorial layers in works of art. Identification processes using reflectance spectroscopy usually involve a spectra database. At the "Centre de Recherche et de Restauration des Musées de France", the database is made up with the spectra of more than 150 dry powdered mineral pigments. However, most of the pictorial layers cannot be modelled as a single dry powdered pigment. On the contrary, pigments are sometimes used in mixtures and usually spread in a binder. These two characteristics of pictorial layers enabled the definition of two major research areas for this work. I. Characterization of pigments mixture Kubelka-Munk theory has appeared to be the most relevant modelling tool to describe the path of light through pictorial layers. In this theory, pigments are characterized in terms of their absorption and their scattering abilities. Assuming linear variations of the absorption and scattering coefficients, Kubelka-Munk theory has enabled a quantitative interpretation of reflectance spectra. Indeed, in most cases, numerical treatment of spectrophotometric measurements performed on a binary mixture now leads to the identification of the components of the mixture. Once the components are identified, their respective proportions can systematically be evaluated. We had the opportunity to apply these results on a real work of art : the Annunciation Virgin by Giovanni di Paolo. On this Italian painting of the XVth century, the color of the skin is produced by a mixture of lead white and vermilion in an egg-tempera medium. Kubelka-Munk treatment of spectrophotometric measurements implemented on this paintings led to values of pigments proportions that are compatible with an evaluation based on optical microscopy imaging. II. Influence of the binder We benefited from the help of a contemporary painter who prepared mock-paintings for these experiments. He used ancient recipes to prepare numerous samples : pigment volume concentration and the number of layers are different from one sample to another. The samples were studied using spectrophotometry, X-ray diffractometry and X-ray microfluorimetry. The results obtained by these three analytical techniques are in good agreement. For instance, Rietveld refinement of diffractogramms and Kubelka-Munk treatment of spectrophotometric measurements lead to the same results in terms of pigment volume concentration for the pictorial layers of the mock paintings analyzed. The outcome of this research work should enable conservation scientists, curators and restorers to see the performances of diffuse reflectance spectroscopy as an analytical technique that provides both qualitative and quantitative analyses of the components of pictorial matter. Besides, measurements are non-invasive, without any contact and can be implemented in situ, without having to move works of art under investigation from their conservation place.
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https://tel.archives-ouvertes.fr/tel-00010271
Contributor : Guillaume Dupuis <>
Submitted on : Sunday, September 25, 2005 - 8:51:02 PM
Last modification on : Thursday, December 5, 2019 - 11:34:04 AM
Long-term archiving on: : Friday, September 14, 2012 - 2:40:11 PM

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  • HAL Id : tel-00010271, version 1

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Guillaume Dupuis. Couleur de la matière picturale : caractérisation des pigments et des mélanges de pigments, effets induits par l'adjonction de liant et de charges. Matériaux. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00010271⟩

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