Black oxide is the conversion coating formed by a chemical reaction with the iron in metal to form an integral protective surface.... contrasted to an applied coating which bonds to the metal but does not react chemically. A black oxide conversion coating is applied to ferrous alloys when a blend of caustic, oxidizers and additives react with the iron to form magnetite (Fe3O4), the black oxide of iron. Black oxide coatings are offered under a variety of trade names including Black Magic, Black Pentrate®, Black Passivation, Gun Bluing and others. Black oxide will not affect the part dimension, hardness, temper or surface properties..... a polished surface retains its gloss and a dull surface finish will retain its matte finish. Black oxide will not chip, peel, flake or rub off. Hot black oxide is a conventional hot (285 F ̊) process which produces a true black oxide iron magnetite. All the benefits of black oxide are available from the “hot” oxidizing process