The Chromic Acid Anodizing, CAA, was the first commercial anodizing process patented in 1923 by Bengough and Stuart, followed closely by the first Sulfuric Acid Anodizing (SAA) process patented in 1927.
The oxalic acid was introduced by the Japanese in the middle of the 1950´s. The main interest today is as an additional acid in Hard Coat Anodizing (HCA) to produce a harder coating faster than obtained with a pure sulfuric acid electrolyte.
Phosphoric Acid Anodizing (PAA) and Boric Sulfuric Acid Anodizing (BSAA) are both developed by the Boing Company, the first one as a structural bonding surface and the other as a replacement for the Chromic Acid Anodizing for non-critical fatigue parts.
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