A number of black coatings are
available commercially to be used on different metals. Black oxide is the
coating that is most often applied to steel. It is applied in a high
temperature (about 290 degrees F.) Alkaline solution. It is especially useful
because of its deep black color and the fact that it has no dimensional
build-up on machined parts.
Black oxide, however, has very poor corrosion
prevention properties. To enhance corrosion properties and lengthen shelf-life,
an oil, wax, or water lacquer sealer may be applied. Once these secondary
coatings are removed, the black oxide will wear or corrode rapidly.
Black oxide on steel is electrically
non-conductive. A rainbow color effect may be noticed, but this effect can be
reduced by using a final sealer. Black oxide can also be applied to stainless
steel and copper base alloys.
