BLACKENING CHEMICAL FOR METAL WORKING Common Blackening Processes and Chemicals for Metal Working: 1. Hot Blackening: . Chemicals: Typically involves using an alkaline aqueous solution at high temperatures. . Process: The metal is dipped in a hot bath of sodium hydroxide, nitrates, and nitrites, which react with the metal surface to form a black oxide layer (magnetite, Fe3O4). . Applications: Common for ferrous metals like steel and iron. . Example Products: Birchwood Casey Presto Black® Hot Blackening, Precision Brand Products Black Oxide Kits. 2. Cold Blackening: . Chemicals: Utilizes a room-temperature chemical bath, often containing selenous acid, copper compounds, and other proprietary agents. . Process: The metal is cleaned, then immersed in the solution, where it reacts to form a thin, dark coating. . Applications: Preferred for small parts, low-volume applications, or when a hot process isn't feasible. . Example Products: Birchwood Casey Presto Black® Gel, Caswell Inc. Cold Blackening Kits.