Rapid forensic analysis and identification of "lilac" architectural finishes using Raman spectroscopy

The potential of Raman spectroscopy to discriminate between architectural finishes (household paint) has been investigated using a test set of 51 "lilac" paints and three different excitation wavelengths. The spectra obtained with visible excitation typically displayed a series of intense Raman bands on a featureless fluorescence background but the spectra of all the paints studied had essentially identical bands. With 785 nm excitation, although the same bands that dominated the 514 nm spectra were still observed, other bands with comparable intensity also appeared. The two strongest scattering constituents were identified as a dioxazine dye, Violet 23 and beta-Cu(phthalocyanine). A scatter plot of the intensities of marker bands for these constituents (normalized to the strong rutile bands that were always present) showed that, despite the fact that the sample set spanned a wide range of rutile: dioxazine dye: phthalocyanine ratios, many of the samples had very similar ratios and could not be discriminated. However, all the samples (even those with similar relative proportions of the main constituents) could be discriminated on the basis of their minor constituents, either by manually measuring band intensities or through the creation and searching of spectral libraries.