Black Coatings for Absolute Radiometers

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Abstract
With radiometers in which electrical heating is substituted for radiant heating, corrections are necessary for radiation reflected by the blackened receiver and for the thermal resistance of the black coating. Carbon-black and the common form of gold-black are unsuitable for coating radiometers because their thermal resistances are too high, and an optical lacquer tested has a comparatively high and selective reflectance. For the wavelength range 0.25 - 2.5 μm the best material tested is a different form of gold-black, which entails corrections of about 0.005 of the radiation value because of reflection losses, and of less than 0.001 because of thermal resistance effects. The mechanism of heat transport through the black coatings is discussed.

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