Types of Anodizing

Chromic Anodizing
Utilizing a chromic acid electrolyte this form of anodizing yields the thinnest coatings, only .05 to .1 mils thick. Chromic anodizing is a good choice when a part is complex and difficult to rinse because chromic acid is less corrosive than sulfuric acid used in other anodizing methods. Chromic anodize also reduces the fatigue strength of the aluminum less than the other methods described.
Sulfuric Anodizing
This form of anodizing yields coatings under 1 mil thick. Although it offers mild abrasion resistance it is more durable than chromic anodize. Like most anodizes corrosion resistance is excellent. The most desirable feature of this form of anodizing would be the excellent results from dyeing yielding deep and rich colors.
Hardcoat Anodizing
Also using a sulfuric acid electrolyte, although at a lower temperature, hardcoat anodize's claim to fame is wear resistance. This will produce a Rockwell C-scale rating of 60-70. This makes it an excellent candidate for many wear situations.