Conversion coatings are coatings for metals where the part surface is converted into the coating with a chemical or electro-chemical process. Examples include chromate conversion coating

Chromate conversion coating

Chromate conversion coating is a type of conversion coating used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, and tin alloys. It is primarily used as a corrosion inhibitor, primer, decorative finish, or to retain electrical conductivity. The process is named after the chromate...

s, phosphate conversion coating

Phosphate conversion coating

Phosphate coatings are used on steel parts for corrosion resistance, lubricity, or as a foundation for subsequent coatings or painting. It serves as a conversion coating in which a dilute solution of phosphoric acid and phosphate salts is applied via spraying or immersion and chemically reacts with...

s, bluing

Bluing (steel)

Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface...

, black oxide

Black oxide

Black oxide or blackening is a conversion coating for ferrous materials, copper and copper based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance and for appearance. To achieve maximum corrosion resistance the black oxide must be impregnated with oil or...

 coatings on steel, and anodizing. They are used for corrosion protection, increased surface hardness, to add decorative color and as paint primers. Conversion coatings may be very thin, on the order of 0.00001". Thick coatings, up to 0.002", are usually built up on aluminium alloys, either by anodizing or chromate conversion.