Before you attempt cleaning an old coin, it is important that you know its value. If you are unsure, don't clean it. Some coin dealers prefer the coin to be in its original "discovered" state and cleaning them may lessen their value in the eyes of some collectors. Never clean old coins with commercial jewellery cleaners or metal polishes which are too harsh and abrasive. Cleaning your coins is a relatively easy process and should be done the same day they are discovered to prevent further corrosion from building.
Fill a small glass bowl with white vinegar.
Place coins in vinegar and allow to sit for one hour.
Remove the coins from the vinegar. Using a soft-bristle toothbrush, gently brush them removing all rust stains which have been loosened by the vinegar.
Rinse off the coins with distilled water. Using tap water is not recommended since additives may affect the coins and leave spots.
Dry the coins using a lint-free cloth. Allow coins to air-dry without touching each other which can cause hairline scratches.
Repeat process if rust spots still remain.
The process should take between 90 minutes to two hours.
Never clean a proof or uncirculated coin. Doing so will cause minute hairline scratches on the surface and will ruin the mint lustre.