Question: I operate a small sulfuric acid anodizing line and have a question about chromic acid (Type I) anodizing. When discussing the advantages of Type I anodizing, some say it’s better suited for difficult-to-rinse parts because of the less aggressive attack of chromic acid compared to sulfuric acid on the part.
Integral color anodizing is generally done with organic acids, but the same effect has been produced in laboratory with very dilute sulfuric acid. Integral color anodizing was originally performed with oxalic acid, but sulfonated aromatic compounds containing oxygen, particularly sulfosalicylic acid, have been more common since the 1960s. 
Phosphoric acid anodizing is usually requested by the aerospace industry. It is used as a surface preparation for bonding. There are very stringent requirements for application and inspection of phosphoric acid anodized parts [for aerospace application]. Usually the customer requires a certification before parts can be processed.
Anodizing is a method of increasing the corrosion resistance of a metal part by forming a layer of oxide on its surface. Learn about its benefits. Anodizing is a method of increasing the corrosion resistance of a metal part by forming a layer of oxide on its surface.