| abstract |
Hard, integrally colored oxide coatings are formed on aluminum and aluminum alloys by anodizing the surface to produce thereon an oxide coating while simultaneously producing a desired coloring effect. There is used as an electrolyte an inorganic acid, such as sulfuric acid, together with an additional acid which is either an aliphatic alpha-hydroxy monocarboxylic or an aliphatic dicarboxylic acid, or sulfamic acid, and a metal salt of either of the aforementioned organic acids, such as a ferric salt. The process employs ordinary temperatures, and a current density between about 12 and 60 amperes per square foot. |