Blackening techniques for metal 1. Hot Black Oxide Description: Hot black oxide is a chemical conversion coating typically used for ferrous metals (iron and steel). The process involves a series of chemical baths, including alkaline cleaners, hot black oxide solutions, and rinsing baths. * Process: 1. Cleaning: Thoroughly clean the metal to remove oils, dirt, and other contaminants. 2. Rinsing: Rinse the metal to remove any cleaning agents. 3. Blackening: Immerse the metal in a hot alkaline solution (around 285°F to 295°F) containing sodium hydroxide, nitrates, and nitrites. This causes a chemical reaction, forming a black magnetite (Fe3O4) layer on the surface. 4. Rinsing: Rinse again to remove residual chemicals. 5. Sealing: Apply an oil or wax to seal the surface and enhance corrosion resistance.