Microanalysis of artworks: IR microspectroscopy of paint cross-sections

FTIR microspectroscopy of a highly stratified paint cross-section from a late nineteenth century commercial building is described. The use of a Ge attenuated total reflectance (ATR) microscope objective and synchrotron IR source allow collection of high-quality spectra from a 5 μm × 5 μm area of sample in contact with the Ge-ATR crystal. These measurements reflect the clear distinction between the major components that comprise the different paint layers and, more importantly, reveal differences in the local composition within visually similar regions, assisting in the identification of the minor components of the layer. While responsible for the appearance, intensely colored pigments are often present in low-concentration and give vanishingly weak spectral signatures. When combined with high spatial resolution, the presence of highly pigmented imperfections in the paint layer is shown to provide a means of identification of highly diluted pigments.