VCFERROUS - HOT BLACKENING SALT 1. Surface Preparation: Before the blackening process, the metal surface is thoroughly cleaned to remove any dirt, oil, rust, or other contaminants. This typically involves degreasing and possibly etching the surface to ensure good adhesion of the black oxide coating. 2. Immersion in Hot Oxidizing Solution: The cleaned metal parts are then immersed in a hot oxidizing solution, often consisting of a mixture of various chemicals such as sodium hydroxide, nitrates, and nitrites. This solution reacts with the surface of the metal to form a layer of black oxide.