Black oxide is a conversion finish that provides essential protection – and a distinct black coloring – to ferrous metals by creating a chemical reaction within them. The chemical reaction allows a protective coating to be formed without increasing part dimensions, dulling the part’s luster, or altering the hardness of the metal. Because black oxide does not actually apply a coating that bonds to metal, it cannot chip or rub off. Metal that undergoes black oxide conversion also receives two more distinct advantages: dimensional stability and corrosion resistance. After black oxide, parts can withstand up to 96 hours of salt spray testing with the appropriate post treatment of a rust inhibitor.