•For gold coins, soaking in very hot soapy water works the best.
•For old pennies, soak the coin in vinegar for at least 24 hours.
•For bronze coins — usually ancient coins — soak in distilled water (the minerals in tap water can further taint the coin’s surface if soaking for a long time) or olive oil — olive oil is a very gentle way to clean coins, but you may need to soak them for several weeks.
•Silver, copper, and nickel-clad coins can be soaked in distilled water or, to remove tough stains, white vinegar. A 6-minute soak in lemon juice may also be used on silver coins. This will not only protect the coin but it will help give the coin a finish at the end of the cleaning.