Progress in the application of ATR-FTIR microscopy to the study of multi-layered cross-sections from works of art

As a non-invasive or micro-invasive technique attenuated total reflectance Fourier transform infrared spectroscopic (ATR-FTIR) microscopy is a valuable tool for the analysis of materials in works of art. An application for which it has received growing interest is in the analysis of paint cross-sections. However, FTIR microscope configurations, objectives' geometries and low spatial resolutions, and issues of sample preparation have often hampered the characterization of individual layers or features in cross-sections. With the use of case studies, it is demonstrated here that an ATR-FTIR microscope featuring a crystal of optimized geometry and a viewing capability feature allows characterization of individual layers, or areas within layers, of 10 microm thickness or less in single measurements. Of particular value is a remote aperturing feature which allows the analysis of selected areas within the contact footprint of the ATR crystal. Since the technique is non-destructive, the same area can be analyzed by complementary microscopic techniques such as Raman spectroscopy and scanning electron microscopy with energy-dispersive spectroscopy. Pyrolysis gas chromatography-mass spectrometry was also used in some cases to corroborate the spectroscopic data. The analyses presented provided data which were important in informing art historical interpretation and conservation of the artworks examined.