Discrimination of aged mixtures of lipidic paint binders by Raman spectroscopy and chemometrics

Abstract

This work explores the application of chemometric techniques to Raman spectra to study aged lipidic paint binders. These binders, commonly known as drying oils, were widely used by artists throughout history both individually and in mixtures. We prepared various model samples of the pure binders (linseed, poppy‐seed and walnut oils and egg yolk) and of binary mixtures thereof. These model samples were left to age naturally for six years and further characterized by Raman spectroscopy. A comparative study of the Raman spectral features before and after ageing process was carried out. This showed changes mainly in the bands located at 1267, 1655 and 3011 cm–1, which correspond to vibrations in cis double bonds. Multivariate analysis was performed by applying principal component analysis and partial least‐squares discriminant analysis on the corresponding Raman spectra to test whether spectral differences allowed samples to be distinguished on the basis of their composition. The CH stretching region was found to be especially useful for discrimination between the different binders. Furthermore, good sensitivity and specificity were found in the discriminant analysis particularly for the identification of binders containing egg yolk. The results of these multivariate analyses demonstrated the potential use of both chemometric approaches in the field of Cultural Heritage for drying oil characterization and identification, and also for gaining a deeper insight into the ageing process. Copyright © 2011 John Wiley & Sons, Ltd.