An interpretation of the infrared optical properties of gold smoke deposits is presented together with new experimental results. This interpretation is based on an application of classical electromagnetic theory. The gold smoke deposits are assumed to interact with infrared radiation as if they were sheets of an essentially uniform material which is characterized by an average electrical conductivity small compared to that of ordinary metals. The electrical conductivity of gold black deposits is found to be ~10-5 times that of bulk gold, and the volume percent of gold in a gold black deposit is found to be ~0.2 percent.
LOUIS HARRIS and JOHN K. BEASLEY, "The Infrared Properties of Gold Smoke Deposits," J. Opt. Soc. Am. 42, 134-140 (1952)