The physical mechanism whereby adsorbed layers of transparent material cause a visual darkening of thin indium films is investigated. The indium is observed to be in the form of discrete islands. The wavelength of minimum optical transmission through the indium film does not vary proportionately with the size of the indium island size, as would be expected if Mie scattering were the dominant optical effect. Instead, this wavelength depends on the fractional volume of the indium film occupied by the indium islands themselves, in the manner predicted by Maxwell Garnett theory.
Jesse I. Treu, "Mie scattering, Maxwell Garnett theory, and the Giaever immunology slide," Appl. Opt. 15, 2746-2750 (1976)