Blackening products for metal surfaces Black Oxide Conversion Coatings: These are chemical solutions that are applied to metal surfaces to produce a black oxide layer through a controlled chemical reaction. They are commonly used for steel, iron, and stainless steel. Black oxide coatings can be applied using immersion, swabbing, or spray methods. Patina Solutions: For copper, bronze, or brass surfaces, patina solutions can be applied to create a blackened or antiqued appearance. These solutions typically contain chemicals like liver of sulfur or ammonia, which react with the metal to produce darkened colors. Cold Bluing: Cold bluing is a process used primarily for firearms and other small metal parts. It involves applying a chemical solution, typically containing selenium dioxide or copper nitrate, to create a blackened oxide layer on the metal surface.