Passivation is a chemical finishing process that improves the corrosion resistance of metals—especially those containing iron, like stainless steel. It involves treating the surface with a mild acid solution (typically citric or nitric acid) to remove free iron and contaminants. This results in the formation of a thin, stable oxide layer that reduces the metal’s reactivity and protects it from rust and degradation.

Unlike coatings or platings, passivation does not alter the appearance or dimensions of the part. Instead, it enhances the natural protective properties of the base metal.