Burnishing refers to the formation of a weak protective layer (patina rust) on mostly ferrous surfaces - with the aim of avoiding corrosion. Thin black mixed oxide layers are formed by immersing the components or work-pieces in acidic or alkaline solutions or molten salts. During burnishing, small layer thicknesses of approx. 1 μm are produced, which largely remain dimensionally stable. Burnished coatings are highly porous, which is why only a low level of corrosion protection is achieved. Burnishing is frequently used in machine and tool construction, but also in decorative applications: Here they create an antique appearance, e.g. of screws or candles.