Blackening – Oxidation – a process during which an oxide coating forms on the surface. Oxidation is also known as blackening, because the metal obtains a bluish-black tint. Blackening is the high temperature oxidation of steel which significantly increases the corrosive and partially mechanical resistance of coated parts. It is used as the final operation of production of machine and other equipment parts. These parts acquire a beautiful black colour ranging from plain black to reddish black, depending on the type of oxidized steel.