This can be a very touchy subject when it comes to coins and banknotes too as the general consensus is not to clean coins at all.
So you've found this hoard of coins stashed away for decades and they look a bit grubby. Some are crusty with dirt and green and others are unrecognizable. You'd like to make them look better before you take them to show anyone who may want to buy them.
If any of your coins have a green areas or spots then it is best to remove these coins to a "quarantine" area. This green is called "verdigris" and is like a copper cancer or can develop from pvc residue on coins. It will grow with time and spread to your other coins. Verdigris is very difficult to remove so this is often fatal for the coin.
Coins that are obviously dirty can be run under water (with a very mild detergent) and left to air dry. A short soak in olive oil may remove unwanted gunge. For cleaning corroded coins the damage is already done, they will forever show pitting into the coin surface. This is as far as anyone should go with cleaning. Never rub your coins, this will scratch the surface. If a coin has terminal verdigris it may benefit from a longer soak in olive oil and maybe a gentle prod with a wooden toothpick. This might damage the coin minimally but with the verdigris it's value was limited anyway.
If you came across a valuable coin with verdigris I would always turn to an expert dealer for help. There are many myths including inserting your coin into a potato to clean it which I have never had any success with.
Posted by harrisk at November 1, 2008 1:20 PM
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