Electrocoloring of anodized aluminum: Part II—Using mixed carboxylic acids

Electrolytic coloring is a two-stage process involving a second electrolytic deposition process after sulfuric acid anodizing. The effect is to deposit a suitable metal at the base of the pores of the anodic coat. Initial experiments of electrocoloring after anodizing were carried out in a number of organic acids such as sulfamic, benzoic, gallic, and maleic. In all cases, the coating was found to be streaky, nonuniform, and coarse-grained, and the quality of the deposit was not promising.