Crystalline powders, when pressed into plates at pressures of about 40,000 pounds in.-2., reflect strongly in the infra-red spectrum at wave-lengths characteristic of their functional groups. This points to usefulness of such plates in optical investigations of any materials not available as large crystals.
J. A. SANDERSON, "Metallic Reflection by Compressed Crystalline Powders," J. Opt. Soc. Am. 30, 566-567 (1940)