Try hydrogen peroxide and heating the metal. Start with the drug store concentration of H2O first and also at temperatures below boiling (212 F). Slowly work up to higher concentrations and higher temperatures, if you need to, for speed, efficiency, final looks. Otherwise try heated surfaces and boiling salt water. If you do not like that results, heat the metal as hot as you can, using a remote handle, pour water onto it. This last procedure carries great risk of steam splatter and severe heat burns to the skin, so it must be done with complete body protection from the heat, steam, hot water, and splatter.
