To clean corroded coins, soak them in a weak, non-detergent cleaning solution mixed with distilled water. Use your fingers to rub the coins, or use a cloth, toothpick or toothbrush to gently clean them. Never use harsh jewelry cleaners or metal polish on coins. Seek professional advice before cleaning valuable or collectible coins because cleaning greatly reduces the value of such coins.
Soak severely corroded coins in white vinegar for 30 minutes or more before cleaning. After cleaning, rinse the coins with hot running water, and then pat coins them dry with a soft towel. Then rinse them again, one at a time, in a container of distilled water, which rinses away the impurities in tap water, resulting in a shiny coin. Allow the coins rinsed in distilled water to air dry. To prevent scratching their surface, never rub the coins dry.
Expert coin collectors strongly discourage any cleaning of collectible coins as the practice damages the surface of the coins. If cleaning is necessary under exceptional circumstances, consult a professional. Hobbyists who do not have valuable coins or do not wish to sell their coins in the future may clean the coins to make them more hygienic or attractive.