Bronze disease, also known as copper rot, is not a disease, but a chemical reaction forming on the surface of a coin. It is common on ancient coins, but can also appear on modern coins.
When chloride comes into contact with copper or bronze it can begin a chemical reaction that damages the copper by turning it into green cupric chloride.
How to identify bronze disease?
Bronze disease creates fuzzy green or white colors on the surface of the coin. The green coloration can range from a neon green to a dark forest green.
Bronze disease should come off when scratched with a toothpick or fingernail.
Bronze disease will also likely only appear on a couple places on the coin. If the green does not appear in patches, but all around the coin you may have verdigris.
What is verdigris?
Verdigris looks very similar to bronze disease, however, verdigris is non-damaging and sometimes considered desirable for coins.
To tell if you have verdigris or bronze disease you will check three things:
1.) Does the green coloring come off when scratched?
2.) Is the green color patchy instead of evenly covering the coin?
3.) Are there white spots on the coin as well?
If you answered yes to two or more, then you more likely have bronze disease not verdigris.
What to do if a coin has bronze disease?
First, move your infected copper coin away from your other coins. Bronze disease can be transferred if the coins come in contact with each other.
Unfortunately, there are no easy cures for bronze disease and no way to reverse the damage done. You can help slow the spread by keeping the coin as dry as possible. Try keeping the coin preserved near silica gel or rice to absorb moisture in the air.
This website on ancient coins offers several remedies to slow the spread of bronze disease. You can click here to be redirected.
How to prevent bronze disease on your coins?
The best way to prevent bronze disease it to keep your coins dry. Don’t keep your coins in the bathroom or attic where they may be exposed to high humidity.
If you live in an area with high, year-round humidity, buy some packets of silica gel to keep with your coins. For a quick fix, you could fill teabags with rice to help absorb moisture.
For helpful tips on coin storage and handling, as well as recommended product links check out this article on proper coin storage and handling.
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