The oxide coatings are in fact corrosion products which is a thin, usually less than 2.5 µm oxide with good adhesion. The oxide treatments are done by heat, chemicals, or electrochemical reactions.
- Black oxide treatments are done by proprietary chemicals. Some pastes can be rubbed on surfaces to produce similar results. Black oxide can be applied on steel, copper, and most stainless steel.
- Anodizing is produced by electrochemical conversion. The anodizing process, usually performed on aluminum for protection and cosmetic purposes, builds up both on the surface as well as into the metal. Thin coatings, 2 µm to 25 µm can be coated on most aluminums. Thick coatings from 25 to 75 µm are more durable and abrasion resistant than above chemical conversion oxide coatings. This oxide layer can be made in different colors depending on the post chemistries that are employed. The anodized parts are quite durable and do not tarnish and maintain their cosmetic appearance for a long period of time. Anodized coatings are usually dielectric in nature.
- Gun-bluing-type oxidations are done by heating the metals, generally steel, at 370ºC in a steam atmosphere. An oiled gun bluing provides some atmospheric corrosion resistance, but little protection on wear and other corrosion.
- Chemical baths produce coatings similar to a gun bluing coating by immersion techniques.
