Anodizing

The production of a highly protective and tenacious form of oxide as a coating on aluminum and certain other light alloys. The anodizing process increases the thickness of the oxide film normally present on aluminum by making the metal the anode in a suitable electrolyte such as chromic acid or sulfuric acid. The latter gives a colorless film, which has a mordant action for certain dyes, so that attractive colored finishes can be obtained by immersing the anodized aluminum in a boiling solution of a suitable dyestuff.