Automatic identification system of Raman spectra in binary mixtures of pigments

In an art historical context, pigments identification is exceedingly important for the conservation, interpretation and preservation of art works. In practice, the pigments may have been used in mixtures (or in admixtures) with other pigments to produce special effects or tonal qualities. Binary mixtures are the more frequently mixtures used in paintings; for instance, it is commonly used the mixture of a yellow pigment with a blue pigment to produce green colors. In this situation, the pigments identification is actually done on Raman spectra of pigment mixtures and may turn out to be a complex and tedious task, especially when analyzing spectra with a large number of bands located close together as it is the case of mixtures of synthetic organic pigments. To decrease complexity whilst also speeding up the identification process, a system to automatically identify Raman spectra of binary mixtures of pigments is presented in this work. The system is able to identify the two different pigments in the mixture from spectroscopic signature obtained by Raman spectroscopy. The technique has been proved with mixtures showing its robustness against some of the critical factors that could affect the application of Raman spectroscopy for pigments identification as distortion and wavenumber shifts in key Raman bands due to different measurement environmental conditions. The results led to conclude that the system could be a useful tool to help the analyst to make a decision. Copyright © 2012 John Wiley & Sons, Ltd.