Type I is anodizing that uses a chromic acid based chemical bath. Used mostly for aerospace and Defense Department requirements where a thin coating and a high level of corrosion resistance is desired. It is also used as an excellent primer for paint and other top coats. Note that there are some non-chrome “variants” that usually also fall into the Type I category, such as boric-sulfuric or tartaric anodizing.

Type II is anodizing that uses a sulfuric acid based chemical bath. Used for general and commercial anodizing of aluminum, Type II Anodizing is widely used for everything from toys to sporting equipment to computer hardware. The list is almost endless. Type II can be colored in virtually every color of the rainbow using organic dyes. Type II can also be clear. Type II anodizing is usually the most affordable of the three to bring in-house.

Also called Hard Coat anodizing, Type III anodizing is used wherever a super hard surface is desired. Type III is used in military equipment and weapons, scratch resistant aluminum cookware, commercial pizza pans, sporting goods, and parts with bearing surfaces to name just a few. Type III is not usually colored or dyed. Darker or lighter shades of grey to black are achieved by altering temperature, voltage and bath compositions. 

By Ken Emilio