Evaluation of a principal components-based searching algorithm for Raman spectroscopic identification of organic pigments in 20th century artwork

The characterization of artists' materials is of great importance for the c onservation and restoration of 20th century paintings, and it provides info rmation which is of art-historical interest. The identification of modern o rganic pigments by Raman spectroscopy is hampered by the large amount of di fferent synthetic materials that exist, Therefore, an extended database of reference spectra is needed, Besides this spectral library, there is need f or an accurate and fast-searching algorithm fur selecting the reference spe ctrum that best corresponds with tile unknown spectrum, A principal compone nts-based spectral searching algorithm is proposed that largely reduces the number of data points for each spectrum. By subsequent measurement of the Euclidian distance between the unknown and the reference spectra in the pri ncipal components space, the corresponding reference can be selected. The a lgorithm is tested by using the results of the Raman spectroscopic analysis of different colored pencils. Different qualities of matches for the ident ification protocol could be distinguished. The synthetic organic pigments i n micro-samples of the painting "Fauhourg" by Paul Delvaux could be identif ied by the proposed algorithm.