Bryan C. asks: Is there any way to remove green corrosion from a copper coin? The coin in question is an 1861 British farthing. It would probably grade about VF if not for the corrosion.
Verdigris is the green corrosion seen on copper coins that were in the presence of oxidizer. It’s actually a mixture of two different forms of copper acetate and copper carbonate. Your farthing doesn’t warrant the attention that you are giving it. The coin is easily obtainable in all grades including uncirculated condition. If you want to practice removing verdigris and have a desire for a career in coin restoration you can do the following:
Ask your druggist for copper soap. Rub the coin gently with a moist cloth which has passed over the copper soap with your fingers. Do not smack on the soap. The verdigris will be removed and so will part of the surface of the coin.
I usually frown upon any cleaning of coins because it requires the use of potentially harmful (to people) chemicals. Few coins are improved by cleaning and usually the coin is irrevocably altered. Cleaning techniques are most often useful for coins that have been in the ground or under the ocean for a long period of time. Cleaning of these coins require an expert and experienced hand to restore these coins to a semblance of their original condition.