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Détermination des propriétés optiques de matériaux granulaires

Abstract : The non destructive analysis of works of art and more specificaly the paintings with the aim of a non ambiguous identification of their components and the understanding of the techniques of the artists still remains a challenge. The aim of our research is to elaborate a purely optical way for this identification, based on the exlusive use of the intrinsic characteristic optical parameters (spectral complex optical index) of the components, instead the derived parameters presently commonly used, depending on several other parameters (morphology, environment...). The identification of pigments is usually made by comparison with a reference database of reflectance spectra or at least by K/S, ratio of the absorption coefficient, K, to the diffusion coefficient, S. This model is widely used in industry and is penetrating the domain of the analysis of works of art and cultural heritage. K/S is calculated by using the Radiative Transfer Equation, RTE, solved within the 2-flux approximation (Kunbelka-Munk theory). Its domain of validity is limited (strongly scattering media, hemespherical lightning and detection...). Moreover, K/S depends on the size and shape of the pigments in addition to the optical index of the matrix and pigments. This method is therefore unsuitable for an unambiguous analysis of the paintings and has been often criticized. The alternative approach we propose is based on the resolution of the RTE using the 4-Flux approximation, combined with the Mie theory, allowing the identification of the pigments via the spectrum of their complex optical index entered in the model via a data bank. The key point of this approach is the index data bank. We report in this communication on this crucial step of the method : the determination of the intrinsic optical index of pigments under the form of grains of micrometric size. This step is non trivial and presents a lot of difficulties which are not completely solved. It is one of the reasons why a more rigourous analysis of the paintings has not been up to now developed
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Submitted on : Friday, June 7, 2013 - 11:32:27 AM
Last modification on : Wednesday, November 2, 2022 - 5:52:19 PM
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  • HAL Id : tel-00831549, version 1

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Raphaëlle Jarrige. Détermination des propriétés optiques de matériaux granulaires. Agrégats Moléculaires et Atomiques [physics.atm-clus]. Université Pierre et Marie Curie - Paris VI, 2012. Français. ⟨NNT : 2012PAO66559⟩. ⟨tel-00831549⟩

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