Professional coin collectors advise amateurs not to try cleaning antique coins of significant value at home, because of the damage you can do to the fragile metal surface. Nevertheless, there are good reasons to clean common old coins if you simply want them to look good in your home collection. It's not a difficult job, especially since many of the ingredients for cleaning coins at home are already available on your kitchen shelves.
Baking Soda Solution
This method works especially well with silver coins. Dissolve about a quarter cup each of baking soda, salt and liquid soap in a gallon of water in an aluminum pot. (It must be an aluminum pot for this method to work.) Place your coins in the solution and bring it to a full boil. Take the pot off the stove and allow it to stand for 15 minutes. Rinse the coins in clean water and dry them. If the surface of the coin is discolored, follow this treatment with the baking soda paste treatment.
Baking Soda Paste
Make a paste out of 1 tbsp. baking soda and a few drops of water--the consistency should be like toothpaste. (You can actually use baking soda toothpaste, if you have it.) Rub the paste onto both sides of the coin using your fingers, until the coin is shiny. Then rinse the coin in clean water and dry it. This works with all kinds of coins.
Ketchup or Taco Sauce
Coat the surface of your coin with ketchup or taco sauce and lightly scrub it with a toothbrush. The vinegar and salt in the condiment react with the surface of the coin, taking away the tarnish. Rinse the coin in clean water and dry it. This works best on copper coins.
Salt and Vinegar
Mix ¼ cup white vinegar and 2 tsp. salt in a bowl. Immerse your coin in the solution for about 5 minutes. Remove the coins from the solution, rinse thoroughly in clean water, and dry. This method works best on copper coins.
Perhaps the simplest home remedy for cleaning any type of coin is to gently rub the surface with a common pencil eraser. Keep rubbing the coin until it is shiny.