Burnishing today is almost exclusively understood as dip burnishing, which is a process for black finishing overwhelmingly ferrous materials such as cast iron, low carbon steel, non-alloy or alloy steels. In this process, the iron-containing objects are dipped in highly concentrated, boiling, alkaline-oxidising salt solutions, in which deep black magnetite coatings are formed on the surfaces of the objects, the black shade of which depends on the quality of the material, the surface treatment, and the nature and condition of the burnishing bath.
 
The process is used mainly in order to give the work pieces an appealing appearance and increase their corrosion resistance, while retaining their dimensional stability.