Blackening services for metal parts *Types of Blackening Services 1. Hot Black Oxide Coating . Process: Immersion in a heated alkaline solution to create a black magnetite (Fe3O4) layer. . Applications: Tools, machine parts, firearms, and decorative items. 2. Cold Black Oxide Coating . Process: Room-temperature immersion in a solution to deposit a black coating. . Applications: Small parts, where high temperatures are undesirable. 3. Parkerizing (Phosphating) . Process: Chemical reaction in a phosphoric acid solution to form a dark phosphate coating. . Applications: Firearms, automotive parts, and military equipment. 4. Chemical Patina . Process: Application of acids and other chemicals to create a darkened or colored surface. . Applications: Artistic works, sculptures, and decorative items.