Blackening agents for metal Blackening agents for metal are chemical solutions used to apply a black oxide or patina finish to the surface of metal parts. These agents vary depending on the type of metal being treated and the desired outcome of the blackening process. Here are some common blackening agents for different metals: *For Ferrous Metals (Steel and Iron) 1. Sodium Hydroxide (NaOH) and Sodium Nitrate (NaNO3) Solution - Application: This is the standard solution used in hot black oxide processes. The metal parts are immersed in a hot solution (135-155°C or 275-311°F) that converts the surface to magnetite (Fe3O4). - Example Product: Birchwood Casey’s Tru-Oil Black Oxide Kit. 2. Cold Blackening Solutions Components: Typically contain copper selenium compounds. - Application: Applied at room temperature, these solutions are less durable than hot black oxide but are easier and safer to apply. - Example Product: Birchwood Casey Super Blue Liquid Gun Blue.