Black Oxide is the process of forming a black iron oxide on the surface of ferrous metals, and is most commonly referred to as black oxiding, blackening, oxidizing, gun blueing. This process is most well known for its enhancements in aesthetics, improved lubricity and increased corrosion resistance.
The coating from the black oxide process is a chemical conversion coating. This means that the black oxide is not deposited on the surface of the substrate like nickel or zinc electroplating. Instead, the black oxide coating is produced by a chemical reaction between the iron on the surface of the ferrous metal and the oxidizing salts present in the black oxide solution. After the black oxide process is complete, a supplementary post oil treatment is applied in order to fully absorb into the pores, further creating a deeper black appearance, enhanced corrosion protection and resistance to abrasion.