Pigments and Mixtures Identification by Visible Reflectance Spectroscopy

Abstract

Non-invasive techniques, as well assessed, are commonly used as preliminary investigations on the superficial constitutive materials of works of art.In particular, when the sampling on the artwork is not permitted, non-invasive techniques, such as Visible Reflectance Spectroscopy, can face successfully the problem of pigments’ identification and characterization.Nevertheless, the application of this diagnostic tool could be more difficult when pigments’ mixtures are present in the painting layer. Moreover, the various ratio possibilities among different pigments and the eventual yellowing due to the binder's decay could modify the spectral reflectance behaviour.In this study, about a hundred of standards of different pigments and mixtures have been realized using linseed stand-oil as binder, in order to simulate simple and complex pictorial layers. All the standards were analysed by Visible Reflectance Spectrometry, building up a specific database of reference spectrophotometric curves. Besides, every standard was analysed by XRF analysis and multispectral techniques to implement the database itself.In this paper an extract from the database and some case-studies, among the most interesting and complex ones, will be presented, highlighting the importance of an integrated use of different non-invasive techniques for the identification of pigments and mixtures.