Selenous Acid
Selenous acid protecting and changing the color of steel.
Application
Selenous acid most commonly used as cold bluing process of steel. Mixture of selenous acid, copper(II) nitrate, and nitric acid changes the color of the steel from silver-grey to blue-grey or black. In place of copper nitrate and nitric acid BLUING process can be processed by use of copper sulfate and phosphoric acid with Selenious Acid.