cleaning coins by tooth pick

Och. You missed my point. ANYTHING you do to take away some of the contaminates may well take away some of the metal of the coin.
An example is a Copper Coin. First all Copper will combine with Oxygen in the air to form CuO. This further combines with Carbon Dioxide and moisture to form Copper Carbonate. The CuO is just a darkening thing. The Copper Carbonate leaves a sometime greenish patina on Copper. Nitrates in the Air attack Silver. Chlorine, Florine and some other substances attack Gold.
By attack I mean combine with. The removal of this new compound takes away some of the original materials. If something like distilled water or Acetone does not remove whatever you want removed, then any additional attempts would surely damage the coins.
Might as well place coins in Walmart Jewelry cleaners. At least better than a toothpick.
I once placed a Dime in vat of acid and ended up with a fantastically shinny coin but now probably could call it a half dime. :hammer:
Great place for pennies is in Sulfuric Acid. Residue is CuSO4, filtered, allowed to evaporate will leave a fantastic, well proportioned crystal, of clear blue.

 

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Great. Thanks Carl, now you have me itching to make crystal pennies...

 

OK - don't hit me no more.
I think I got it.
Thanks!

 

he didnt tell you but one of his teeth is made of metal. he has a theory that there might be verdigris in his metallic teeth