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