Clean old coins with vinegar.
To clean an old coin with vinegar, pour a cup of vinegar into a glass or bowl, and then gently set the coin at the bottom. Let the coin soak for a few minutes. Then grasp the coin by its edges, pull it out of the vinegar, and rinse it clean with distilled water and dry.
Again use with CAUTION, Vinegar is corrosive and has the possibilty of damaging a coin surface