The Preparation and Optical Properties of Gold Blacks*†

The optical properties of gold smokes deposited on cellulose nitrate films under different experimental conditions have been studied. The conditions of pressure of the inert atmosphere, purity of the gas, rate of evaporation, and the distance between source and deposition surface giving the highest infra-red absorption per unit mass have been found. The thermal mass required for high infra-red absorption is small compared to the thermal masses of other receivers used for infra-red measurements. The gold “blacks” turn yellow and have lower infra-red absorption when heated above 110°C.Gold “blacks” with very high infra-red transmission (3–15μ) and low transmission at shorter wave-lengths are prepared when oxygen is present in the “inert” atmosphere.The particle size and particle distribution of the gold smokes deposited under different experimental conditions have been investigated with the electron microscope at high resolution.