Pickling is designed to achieve the rigorous cleaning and activation of metal surfaces through the removal of a thin layer of the material processed. The result is a metallically pure surface, free of oxides and contamination of other metals. Primarily attacking the grain boundary of the metal structure, it gives the surface a matt to satin gloss appearance.
Passivation is the treatment of stainless steel with a mild oxidant, (acid solution), intended to remove free iron and other foreign matter from its surface, for the purpose of improving corrosion resistance, by enhancing the formation and structure of the stainless steels naturally forming corrosion-resistant passive layer. Permanent corrosion resistance and passivity in the production processes are the main reasons for using stainless steel. In addition to the decorative aspects, this can be influenced by the selection of surface treatment used.