An explanation for the black colour of "black nickel”

Abstract

An explanation for the appearance of black nickel deposits is offered; it arises from a decreased reflectivity. Qualitatively, this decrease in reflectivity could be considered as arising from a decrease in the effective electron density resulting from a dispersion of the metal in a dielectric matrix. A quantitative theory based on the optical constants of the mixture as a function of composition is given. It is shown that when the metal content of the deposit is small, the optical constants are such as to give low reflectivity at sufficiently large thicknesses.