On the basis of Brewsterian angle measurements, a procedure is here outlined which yields refractive indices with uncertainties in the third decimal place. Since “bulk” refractive indices are desired, it is shown that the errors due to surface films may be eliminated by making measurements only on freshly ground and polished surfaces. Attention is directed to applicability of this procedure when the refractive indices of black materials are to be determined.
A. H. PFUND, "The Brewsterian Angle and Refractive Indices," J. Opt. Soc. Am. 31, 679-682 (1941)