Mirror polishing is most commonly carried out on stainless steel as it doesn't require any protection to prevent tarnishing. Brass, steel, aluminium and zinc will all require a protective coating after polishing. This can be in the form of a lacquer, wax or oil.
If the item is being polished in readiness for an electroplated finish such as nickel or chrome, the polishing process is slightly different. Electroplated finishes tend to highlight any imperfections in the metal and must therefore be completely removed at the first polishing operation.