Identification of pigments in paint cross sections by reflection visible light imaging microspectroscopy
Anal. Chem. , Volume 75 p. 716- 722
A setup for reflection visible light imaging microspectros-copy (VIS-imaging) as well as its evaluation and applica-tion is described and tested. The spatial resolution of the system is ~1 µm at a spectral resolution of 4 nm. The optical contrast between different colored particles in the surface of a sample is optimized with a new image processing method for mapping of the distribution of the identified pigment particles. The potential of VIS-imaging in the study of paint cross sections obtained from paint-ings is explored. Spectra obtained from pigment particles in these cross sections result in classification or identi-fication of several pigments. The investigated paint samples are challenging test cases, as they contain several colored materials with a very fine distribution. VIS-imaging can identify and map the most common traditional blue pigments, i.e., smalt, azurite, ultramarine, and indigo in 17th century oil paintings. Smalt can be identified even after complete discoloration. VIS-imaging analysis assisted in the identification and mapping of modern synthetic red and yellow pigments in a 20th century painting.