Black oxide coating, also known as blackening, blackening treatment or gun bluing, is a chemical conversion coating that forms a black oxide layer on the surface of ferrous metals. This process involves a reaction between the metal surface and a chemical solution.

The black oxide coating serves several purposes.

• Provides a decorative and uniform matt or gloss black finish, depending on the surface preparation, enhancing the appearance of metal parts.
• Helps improve the corrosion resistance of the metal by creating a protective layer that acts as a barrier against moisture and oxidation.
• Additionally, the black oxide coating can provide some level of abrasion resistance and friction reduction.

The applications of black oxide coating are widespread and commonly used in industries such as automotive, firearms, and machinery manufacturing. It is applied to various metal components, including screws, bolts, nuts, tools, firearms, and even musical instruments, to provide both aesthetic appeal and corrosion protection.