Regular-reflection IR spectroscopy is revisited in view of non-destructive in-situ analyses of historical varnishes. The angle dependence of the average level of reflectance as well as of the sign and the amplitude of the dispersion-like features the reflection spectrum consists of, are discussed. The close relation between the reflectance spectrum at the Brewster angle and an absorbance spectrum is illustrated by an experimental example.
E. H. Korte,
"Regular-Reflection IR Spectroscopy Of Historical Varnishes", Proc. SPIE 1145, 7th Intl Conf on Fourier Transform Spectroscopy, (1 December 1989); doi: 10.1117/12.969469; https://doi.org/10.1117/12.969469