A chemometric study of ageing in lead-based paints

The development of non-invasive analytical methods is of widespread interest to the field of conservation science, providing chemical insight into the materials used to create painted works of art, which can, for example, inform decisions about their restoration and preservation, or help discern original works from forgeries. A key undertaking in this area is to develop practical methods for identifying and understanding the chemical processes that occur in paint films under ageing. Furthermore, whereas a number of scientific studies have focussed on model systems in which natural ageing processes are simulated in a short time by irradiation under ultraviolet (UV) light, it remains to be established to what extent natural and accelerated ageing induce similar chemical changes. In this work, we employ FT-Raman spectroscopy, together with a simple spectral-deconvolution algorithm, to study in detail the spectral changes accompanying the natural and UV-accelerated ageing of lead-based paint films. We find that the two processes differ significantly, and that spectroscopic signatures, principally in the fluorescence background, can thus be used to differentiate the two modes of ageing and hence possibly to identify attempted forgeries. Our studies also suggest that paints based on proteinaceous binders are more stable to ageing than lipid-bound ones. Finally, we investigate the possibility of using our chemometric deconvolution technique, in conjunction with multivariate analysis, for the semi-automated characterisation of the degree or extent of ageing in unknown samples.