Polishing removes a small amount of the metal. Be especially careful of over polishing plated items. Be sure to rinse off all residue of cleaner and oil. Avoid harsh abrasives such as coarse steel wool on copper and brass. According to some experts, chemical cleaners, especially those with ammonia, are not recommended due to possible damage.
Some cleaners contain acids or chlorides which can start new corrosion.
Remove all traces of cleaners. Residue of cleaners containing ammonia can also cause corrosion. Wash carefully if they are used. Lime deposits can be removed on copper with laundry water softener. Avoid placing items near objects containing sulphur or chlorides.