One of the anodic-oxidation processes discussed is the Veroxal process which produces films characterized by special high hardness and characteristic coloration. The Veroxal process produces films with tints from silver yellow over brown and various bronze tints to black. The colorations are absolutely light proof and are all obtained with the same bath composition. The color differences are obtained by employing different alloys and, to a limited extent, through different film thickness. Shading of color can be obtained by employing different densities and bath temperatures.
Neuere Erkenntnisse und Erfahrunden ueber veschiedene Variationen der anodischen Oxydation des Aluminiums, trans. of Aluminium (West Germany) v39 n7 p424-8 Jul 1963.