Multivariate analysis of combined Raman and fibre-optic reflectance spectra for the identification of binder materials in simulated medieval paints

The non-invasive identification of paint materials used in works of art is essential, both for preserving and restoring them, and also for understanding and verifying the history surrounding their creation. As such, the development of suitable non-invasive techniques has received much interest in recent years. We have investigated the use of Fourier transform (FT)-Raman spectroscopy and fibre-optic reflectance spectroscopy (FORS), together with multivariate principal-component analysis (PCA) techniques, in order to identify the pigment and binding materials used in made-up samples representative of real artwork. We demonstrate that both types of spectroscopy provide complementary information which can be used to identify the pigments and binders in paint samples. We show that PCA with FT-Raman spectra can be used to assist in the identification of oil-based binders, and that the additional data provided by FORS spectra enables PCA on combined spectra to identify more complex proteinaceious and polysaccharide-based binding media. The results presented here demonstrate that multivariate analyses of lead-based paints, using data measured by FT-Raman and FORS in conjunction, have much potential for identifying individual pigments and binders in paint samples. This provides a path towards computer-assisted characterisation of paint materials on artwork.