how to clean a nickle coin?

Nestor Klan: You're not supposed to clean them because it ruins them and lowers its value Tarnished coins are worth more than cleaned

Lionel Tanen: If it's got loose "stuff" (dirt, etc.), you can try soaking it in olive oil for a couple of days to see if it works loose.If the olive oil doesn't float the junk off, then it's actually part of the surface of the coin, and anything you do to remove it would hurt any collector value it might have.