Determination of the optical absorption coefficient of powdered materials whose particle size distribution and refractive indices are unknown.

A method has been devised, based on the Kubelka-Munk theory of diffuse reflectance, for obtaining an estimate of the optical absorption coefficient of a finely powdered material that has been collected on the surface of a membrane filter. The procedure does not require any knowledge of either the real refractive index or particle size distribution of the material. No mechanical or chemical processing is involved, and only one sample is required. Results are presented.