Green Cover On Coins

to the community.

What you are seeing is called "Bronze Disease". Here is a web site that will explain what it is and give you some methods to correct it. http://www.classicalcoins.com/bronze_disease.html

Yes, if not treated it will destroy the coin.

Patina is caused on bronze of or copper coins, etc by oxidation over long periods of time. This is stable and should not be removed.

Welcome to CC!

The green is not oxidation, it is VERDIGRIS. Plain and simple, you can call it "bronze disease" or whatever you like, it is in fact verdigris. My definition of verdigris:




When you have heavy verdigris, such as on ancient coins, you usually don't want to remove it. Doing so will leave behind significant surface damage and you'll often lose detail in the coin. The verdigris salts will actually follow the coin design, especially when it's heavy.

The best thing to do, if you don't want to attempt conservation, is to protect the coins from the verdigris feed materials. This includes contact with other coins that have verdigris. First, neutralize the verdigris acids. I recommend a very slightly alkaline mixture of deionized water with a very tiny bit of baking soda. One third of a teaspoon in a gallon of water is sufficient. Soak the coins in that for a day then allow the coins to fully dry. Next, rinse them with a high-quality acetone to completely dehydrate the verdigris. Finally, store the coins in completely air tight holders, such as Air-Tite brand, so that the verdigris feed materials are no longer able to get to the coin.

With all due respect Mr. Thad, patina and verdigris are NOT the same thing. Verdigris is not an oxidation process. The formation of a patina (or a tarnish if you prefer)is. Oxidation (patina)on bronze helps preserve the metal beneath it whereas verdigris, like rust on iron, corrodes it. Read the article on "bronze disease" the link for which was posted earlier in this thread by echizento, to clarify what this conversation was about. And please temper your overconfidence; you're not the only one who knows what he's talking about.

I agree, a green patina on ancient coins is not Verdigris. I am not a chemist so I can not explain the chemical process that causes this effect. But ancients coins that have been buried in certain types of soil for a two thousand years or more will develop a beautiful green patina. This effect is desirable and can increase the value of the coin.

On the other hand Verdigris or Bronze disease can also form on these coins that have been buried in a damp environment. I have found that these coins have lost most if not all of their patina and the metal has also suffered damage.

Thanks for the welcome jbuck...I'm glad to be here it is a great forum...and I'll stop splitting hairs on this...I just took umbrage to the tone of his post but I can also learn to thicken my skin...

to the Forum of argumentations.
Not meaning to continue possible discrepancies about what is on your coins but withoug actually knowing how those coins were and are stored, how long they were there, etc., it is not to easy to say what is on those coins. If those are in fact a Copper based coin such as Brass or Bronze which are mixtures of Copper and other materials, it is really difficult to say what is the nature of that greenish patina. For all anyone knows it could even be a greenish paint applied by someone in the past as a preservative.
However, if it is rather lumpy, the chances of it being something that combined with the original material of the coin is much greater than just paint of some form of substance applied to the coin. In the past some have actually applied Varnishes, Lacquers, etc. to coins for such prservationing.

Basically what has been noted already as far as not removing the greenish stuff if you don't know what your doing is the smartest procedure. Encapsulating those coins as much as possible in something that is air tight would be the smartest procedure.

Ever watch the Antique Road Show? If so you'll hear them say many, many times that if you had left that alone and not tried to clean it, it would have been worth much, much more. That could well be your coins. Removing that substance may well leave massive potting, scratches, dents, etc all over the place where some metal has been lost.

Amd as far as Oxidation of coins goes. In most instances Copper coins are attacked by Oxygen only slightly. Same with Copper piping in and around houses. The Copper darkens as it becomes Cu2O. However, this readily combines with Carbon Dioxide and moisture in the air to form that greenish patina called Copper Carbonate.

The worst thing about Copper is in some areas where Sulfur rich Coal is burned, power plants and steel mills, the Sulfur is pumped into the air as SO or SO2, which mixes with the moisture in the are to form an acid. This is what is called Acid Rain and it ruins statues, household piping, your Copper coins and almost anything else.

In some areas, such as Illinois, the electric companies have gone to Lead Covered Copper wires and Stainless Steel rods for their grounding systems due to this. Even Copper grounding systems in the ground have vanished into Copper Sulfate due to the Acid Rain.

Actually if you do get a chance to visit a power station in Illinois, you would see that all the exposed grounding systems appear to be Aluminum. Those are not Aluminum. Those are all Lead Covered Copper cables.