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Proceedings Paper

UV-fluorescence spectroscopy for identification of varnishes in works of art: influence of the underlayer on the emission spectrum
Author(s): Mady Elias; Caroline Magnain; Carlos Barthou; Austin Nevin; Daniela Comelli; Gianluca Valentini
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Paper Abstract

The identification of varnishes may be essential for the choice of the appropriate solvent during their removal by restorers. This recognition is obtained by UV-fluorescence emission spectroscopy with a quasi-monochromatic UVexcitation. A new portable instrument has been developed in order to implement non-destructive, contactless and in situ measurements, providing results in real time. The method is applied to the analysis of a real ancient painting. The resin-based varnish, the recipe and the state of degradation of the varnish are deduced in different locations of the painting by comparison with a database of reference varnishes. Moreover, spectral data are compared with the Fluorescence Lifetime Imaging (FLIM) analysis, performed on the same painting. Different areas containing the same varnish can then be localized on the whole painting. These results show that both UV-fluorescence methods are complementary for rapid and in situ analysis of varnishes of an entire work of art. Nevertheless, the paint layer beneath the varnish modifies the varnish fluorescence spectrum thus complicating its recognition. Indeed, the possible fluorescence of the binder of the paint layer or its reflectance spectrum must be taken into account. A systematic experimental study on fresh and aged model samples made of different varnishes, pigments and binders is presented in this work. It shows that UV-fluorescence emission spectra and diffuse reflectance spectra must be coupled to extract the fluorescence of the single varnish. Both spectra can be recorded by the presented instrument. A new theoretical approach is summarized in order to explain this phenomenon.

Paper Details

Date Published: 1 July 2009
PDF: 12 pages
Proc. SPIE 7391, O3A: Optics for Arts, Architecture, and Archaeology II, 739104 (1 July 2009); doi: 10.1117/12.825093
Show Author Affiliations
Mady Elias, Institut des nansciences, CNRS, Univ. Pierre et Marie Curie (France)
Caroline Magnain, Institut des nansciences, CNRS, Univ. Pierre et Marie Curie (France)
Carlos Barthou, Institut des nansciences, CNRS, Univ. Pierre et Marie Curie (France)
Austin Nevin, ULTRAS-INFM, CNR, Politecnico di Milano (Italy)
Daniela Comelli, ULTRAS-INFM, CNR, Politecnico di Milano (Italy)
Gianluca Valentini, ULTRAS-INFM, CNR, Politecnico di Milano (Italy)

Published in SPIE Proceedings Vol. 7391:
O3A: Optics for Arts, Architecture, and Archaeology II
Luca Pezzati; Renzo Salimbeni, Editor(s)

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