Contact Verdigris

BadThad · Feb 17, 2010

Just thought I'd share a little section from my upcoming book. I found a beautiful example of contact verdigris today so I've added some pictures to this section:

THE SPREADING OF VERDIGRIS
In some ways verdigris is like a bacterium or virus. It's obvious after looking at the chemistry involved that it can spread from coin to coin by contact. It's a simple matter of the verdigris infected coin being a donor of the corrosive elements. Since verdigris is an active spot on the coins surface that is constantly undergoing change based on composition, hydration and temperature, the chemical equilibriums dictate that some of the counter-ions (acetate, hydroxide, carbonate, etc.) will be present. If that verdigris stays in contact with a fresh copper surface, some of those ions will naturally migrate. Once they have moved to the new surface, cupric compounds will start to form producing new verdigris. As the spot is continually fed by the donor coin and by exposure to air and water, the verdigris will grow. Isolation of coins from the verdigris feed materials is of utmost importance to the numismatist!
Collectors should always separate verdigris infected coins and quarantine them! They will act as a catalyst for the continual formation of verdigris via ion migration.
Here's an example of how verdigris can spread by contact. This "mated-pair" was found inside of an old roll of coins. The coins were literally stuck together. The rest of the coins in the roll were in excellent condition so it is obvious that the verdigris on the problem coin prompted the formation of verdigris on the non-infected coin.
This is a picture from above the mated-pair:
Click to expand...