Bronze Rot on Ancient Coin

What To Do If A Coin Has Bronze Disease?

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.

Image Courtesy of Wikipedia.

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.

The Statue of Liberty’s coloring comes from Verdigris!

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.


Share any questions or comments below!

Nickel with Soap, Lemon, Baking Soda

Cleaning Coins is Actually Bad For Them (with pictures!)

Post on any coin forum asking how to clean your coins and you will be accosted with angry coin collectors tell you to absolutely not try to clean them. There is good reason for this.

Although a cleaned coin may look better to the human eye, it actually damages the coin.

After being exposed to oxygen, water, and other elements in circulation, coins develop a patina. The patina is a thin layer of green or brown film caused by oxidation on the surface of the metal.

Cleaning a coin involves removing the thin layer of patina on the top of the coin to expose the shiny metal below. From afar, the coin would be shinier and look newer.

In reality, the cleaned coin now has very small scratched called micro-abrasions. These small scratches hurt the coins value for most collectors. Plus, by giving the coin a more scratched surface, the coin is now more prone to oxidation.

Here are the coins I will be using to show the different cleaning methods sometimes prescribed.

1.) 196(?)D Nickel – Dish Soap, Sponge, Lemon, and Baking Soda

This coin was the worst of the bunch. I could only barely make out the first part of the year (maybe 1968 or 1969?).

Since this coin was the worst of the bunch, I decided to use the most abrasive cleaning methods on it.

First I used a sponge with Dawn Dish soap aggressively on the surface of the coin. As I ran hot water over the coin I continued to rub in circular motions.

After this, it looked a bit cleaner, but I decided to get some chemistry involved and let the coin sit in lemon and baking soda before I rubbed it with a Q-tip.

The obverse of the coin after cleaning.

The coins look ever so slightly better after being cleaned. However, the amount of long term-damage done is not worth the small increase in eye-appeal. The date was still illegible after cleaning.

2.) 1986D Penny – Lemon and Baking Soda

For the 1986D, I put the penny in a small glass ramequin with fresh lemon juice and added about half a tablespoon of baking soda. I could tell something was happening as the concoction began to fizz!

Penny soaked in lemon juice and baking soda.

After letting the coin sit in the mixture a minute, I flipped it over so it could effect the coin evenly. Once that side was done I took the coin out to rub it with a Q-tip.

The coin certainly came out much shinier! If I had been more aggressive with the Q-tip, I could have gotten it much cleaner.

The obverse before (left) and after (right).
The reverse before (left) and after (right).

Much shinier of course, but you can still see small sections where the q-tip scratched the surface of the coin.

3.) 2000D New Hampshire Quarter – Acetone and a Q-tip

This coin was pretty clean already. Just a few blemishes keeping it from looking like new. For this quarter, I decided to go for a gentler cleaning method.

I took a Q-tip, dipped it in acetone, and used gentle circular motions on the surface of the coin.

Gunky!

This worked effectively and quickly, removing dark spots in the corners of the coin. Here is the before and after comparison:

(Sorry! The before image is not very clear.)
Again, not very clear image. Sorry!

4.) 1995D Penny – Acetone ONLY

If I had to recommend a way to “clean” a coin, this would be it. Acetone, also known as propanone, only dissolves organic materials. It can help dissolve glue, wax, and plastic.

This penny looks to be experiencing copper rot, more formally known as bronze disease. This occurs when copper comes into contact with chloride. You can tell by the green and white spots on the surface of the coin.

(Coins can also be affected by verdigris which is very similar, but I suspect this is bronze disease because of the white spots along with the green.)

To use acetone and minimize damage to the coin, you need to use 100% pure acetone. Don’t use nail polish remover as it includes coloring and fragrances that could affect your coin.

Keep pour the acetone into a glass jar or bowl. Put the coin into the acetone and try to move the coin as little as possible. You do not want the coin to scratch across the glass.

Penny in acetone in a glass bowl.

I would lightly swish the acetone around, but not enough to move the coin. After about 5 minutes I flipped the coin over and let it soak for another 5 minutes.

When taking the coin out of the acetone make sure to let it AIR DRY. Do not pat the coin dry with any material as this can also cause small abrasions. Acetone dries very quickly.

Obverse before (left) and after (right).
Reverse before (left) and after (right).

The obverse of our 1995D penny actually looks slightly worse after the acetone bath. The acetone ate away organic material on the top layer of the coin to help reveal the zinc below.

Even acetone cannot save a damaged coin, but it doesn’t hurt the metal when done properly. (Some people claim that leaving copper in acetone for too long can damage the coin, I don’t recommend leaving a penny in acetone for longer than a half hour.)

Conclusion

I know that by showing coins going from dirty to clean it may look like I am promoting for people to clean their coins. On the contrary, I think it is important for collectors to know that a cleaner coin is not necessarily better.

If a coin looks suspiciously clean for its age, then look carefully! Check for small scratches on the surface that could indicate cleaning. Get a magnifying glass of some kind to check for tiny abrasions that follow similar circular patterns.

Look at all the small scratches on this quarter!

If you have a coin that is both dirty and valuable, you can submit it to a professional coin service like PCGS or NGC to have it professionally cleaned (also referred to as restoration or conservation).

Have you ever cleaned a coin? Vote in our poll or comment below!

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