Cleaning the tarnish off coins is a fairly simple procedure and there are a variety of ways to accomplish the task. However, it is not always advisable to remove the tarnish. If you are planning on selling the coins, be aware many coin collectors prefer coins in their original, aged state. Additionally, if a coin is old or very valuable or you do not know the value of a coin, have it appraised before you clean it as cleaning solutions can sometimes cause small spots, scratches or pockmarks that can reduce the value of a coin.
Place the coin in enough lemon juice to cover it and leave it sit for a few hours, but no longer than 24 hours. The length of time varies with the amount of tarnish on the coin. Clean the coin with a soft brush. Rinse the coin with water and dry with a soft cloth. Repeat as necessary.
Clean off small amounts of tarnish using an acid fluid like warm vinegar or sour milk. Put the liquid on a soft tissue or raw potato cut in half and rub the coin with it until the tarnish is removed. Rinse with water and dry with a soft cloth. Repeat as necessary.
Purchase a ready-made metal cleaning product (available at most stores) and follow the manufacturer's directions for removing tarnish. This method is very fast but does not allow you to stop and repeat so it leave the coin with an oxidized effect and is more likely to cause damage to the coin. Lemon juice or acid fluid are better choices for more control of the cleaning process.