Fourier Transform Infrared microscopic imaging of an embedded paint cross-section

Fourier transform infrared imaging is presented as a new analytical approach in the study of paint cross-sect ions. Analytical FT-IR reflection imaging provides the spatially resolved acquisition of infrared spectra with a resolution of about 7 µm. The technique reveals detailed information on the organic functional group distribution in the individual layers of embedded paint cross-sections and is used complementary to visual microscopy and scanning electron microscopy/energy dispersed X-ray spectroscopy (SEM-EDX). This method was applied to a paint cross-section of Rembrandt's Portrait of a Standing Man (1639). FT-IR imaging of this cross-section identified and localized different compounds present in the layers of this sample. Identification of these compounds based on their infrared spectra is confirmed by results from art historical and conservation literature. Special attention was given to a discoloration that was observed in large parts of the described painting. This discoloration was clearly visible in the paint cross-section. A hypothesis on the nature of the discolored paint layer is formulated based on the FTIR imaging results.