Blackening Chemicals For Metal Working - Blackening chemicals are used in metalworking to create a black oxide coating on metals, which can enhance their appearance, provide mild corrosion resistance, and reduce light reflection. Here are some common blackening processes and chemicals used for different metals: 1. Cold Blackening - Iron and Steel: . Chemical: Selenium Dioxide (SeO2) . Process: The metal is immersed in a solution containing the chemical at room temperature. A reaction occurs, creating a black oxide layer. 2. Hot Blackening - Iron and Steel: . Chemical: Sodium Hydroxide (NaOH) and Sodium Nitrate (NaNO3) . Process: The metal is dipped into a series of hot chemical baths. The process typically includes cleaning, blackening, and sealing steps at elevated temperatures.