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FORVM`s Classical Numismatics Discussion Board  |  Numismatic and History Discussions  |  Coin Photography, Conservation and Storage  |  Topic: Bronze Disease query... 0 Members and 1 Guest are viewing this topic. « previous next »
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E1776
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« on: May 15, 2018, 06:13:30 am »

I am new to collecting Roman bronze and was wondering how much of a worry Verdigris/Bronze disease really is. I have seen several coins with an attractive green patina, but I am concerned that it may eventually change over time. Am I being overly cautious or should I just stick to silver?

Any input would be great. 
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shanxi
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« Reply #1 on: May 15, 2018, 06:29:46 am »

Attractive green patina is not the same as bonze disease. The attractive patina is quite hard and stable. It is mainly  Malachite, a copper carbonate. It's no danger, on the contrary, it protects the coin.

Bronze disease (copperchloride) is light green, powdery, and dangerous. Click on "Bronze disease" for more information (numiswiki).


Fortunately bronze disease is easy to remove, but you have to treat the coin after removal. There are several recipes. Personally I use a 3wt% BTA (1H-Benzotriazol) solution in pure (99.9%) Ethanol after manualy removing the  bronze disease, and it never came back. Some people use wax, but I don't like it. It often gives the coin an "unnatural" shiny appearance.

For Benzotriazol you can read the section "Corrosion inhibitor" in Wikipedia.

https://en.wikipedia.org/wiki/Benzotriazole
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Joe Sermarini
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« Reply #2 on: May 15, 2018, 02:45:28 pm »

Bronze disease is not a significant problem if you keep your coins in a climate controlled space. It can be a problem in high humidity. Even then, it is only an issue for the few coins that actually have bronze disease, which is not patina. Years ago I set aside a couple dozen coins (many different types) that I suspected had bronze disease. I intended to treat them but never did. They have been in a climate controlled space and have not changed at all. If I had left them in my garage, it would probably be a different story.   
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Joseph Sermarini
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« Reply #3 on: May 17, 2018, 07:17:02 am »

Thanks for the input guys, much appreciated.
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