Mid-Infrared Fiber-Optic Reflection Spectroscopy (FORS) Analysis of Artists' Alkyd Paints on Different Supports

Mid-infrared Fourier transform fiber-optic reflection spectroscopy (mid-IR FORS) is a noninvasive and flexible spectroscopic technique. It is ideal in the art conservation field because of its portability for on-site and in situ analysis of art objects, analyses that require delicate handling, or analyses of objects that cannot be sampled. This paper studies the applicability of mid-IR FORS for the characterization of commercial artists' alkyd paints cast on different supports. As predicted, the quality of the spectra and intensity of characteristic peaks varied according to reflectivity, roughness, and materials used in the supports. The presence of organic binder was best identified by its carbonyl peak (the most intense) and CH(2) stretching peaks; however, this was not sufficient to distinguish between oil and alkyd binders. The differentiation and identification of alkyds and oils must rely on the unique fingerprint peaks. However, in some cases, the fingerprint peaks were difficult to interpret because of strong absorptions caused by inorganic paint fillers, often present in modern paint formulations, resulting in anomalous dispersion and reststrahlen distortions.