Numismatists and serious collectors will tell you to never clean your coins.
At one time it was common practice to clean coins and even use shellac on copper coins to keep their color. Dealers would dip coins in harsh chemicals to remove dirt and grime in order to make the coins more attractive to buyers. But that was in the past. Today, we are more sophisticated collectors and like our coins with as natural of a surface as possible. Because of this, the value of a cleaned coin will drop since it will not be as desirable as a coin with an original surface, regardless of the coin’s overall condition.
In fact, cleaning a coin or altering it to make the coin look better is not only unethical, but it can also be a crime since you would be representing a coin as original and it is not. It is called coin doctoring. This is such a touchy subject for the numismatic community that the Professional Numismatic Guild (PNG), an association of top dealers, spent two years trying to define what coin doctoring really means. In 2012, PNG came out with the following three conditions that indicates coin doctoring (emphasis added):
- Movement, addition to, or otherwise altering of metal, so that a coin appears to be in a better state of preservation, or more valuable than it otherwise would be. A few examples are plugging, whizzing, polishing, engraving, “lasering” and adding or removing mintmarks.
- Addition of any substance to a coin so that it appears to be in a better state of preservation or more valuable than it otherwise would be. The use of solvents and/or commercially available dilute acids, such as Jeweluster, by qualified professionals is not considered coin doctoring.
- Intentional exposure of a coin to any chemicals, substances, or processes which impart toning, such that the coin appears to be in a better state of preservation or more valuable than it otherwise would be. Naturally occurring toning imparted during long-term storage using established/traditional methods, such as coin albums, rolls, flips, or envelopes, does not constitute coin doctoring.
But there may be good reasons to clean collectible coins that may not be considered coin doctoring. Some may have collectibles that could be saved if we could just get the dirt or grime off. Some may have some PVC damage that may not have attacked the surface of the coin and could also be saved.
Another reason to clean coins is if you found the coins with a metal detector buried in the ground. Years of being buried in the dirt probably stored in non-archival materials can take its toll on a coin. These coins can be cleaned to remove the dirt.
The purpose is to remove the foreign substances from the surfaces and not to change the physical properties of the coin.
WARNING: IF YOU ARE UNSURE ABOUT THIS PROCEDURE OR WANT TO CONSERVE A RARE COIN, CONTACT A PROFESSIONAL CONSERVATION SERVICE.
If you want to try to clean your coin, consider using neutral and non-abrasive means, such as soaking your coins in extra-virginolive oil or acetone. Yes, I did say extra-virgin olive oil. Extra-virgin olive oil is as neutral as you can get with a product that has been used to make soaps and other cleaners. In order for olive oil to be branded as “extra-virgin,” it must be made by the natural pressing of olives with no chemical additives and be no more than 0.8 percent acidic. Not only does the purity make for oil that is good for consumption, the natural fats can react with dirt on the coin and naturally loosen it to be easily rinsed away.
When trying to remove PVC or other stubborn dirt, try using acetone. Acetone is a natural solvent, chemically known as an organic compound, that has many uses. Acetone is slightly acidic, no more than two percent by volume, which is not enough to cause damage to coining metals.
If you use acetone you need to use 100-percent pure acetone and not nail polish remover. Although nail polish remover does contain acetone, it also contains perfumes and is diluted to the point that it will not work on your coins. The additives will damage the coin’s surface. Acetone can be purchased at your local hardware store and is sold either by the quart or gallon. While shopping, you should also purchase protective gloves (made from powder-free latex or nitrile), a protective mask for your nose and mouth, and something for your eyes if you do not wear glasses. Always remember your safety when using any chemical!
You should never use vinegar or soap. Vinegar is acidic and could affect the surface of the coin. Using vinegar can cause the small scratches and imperfections from the minting or bagging process to become more pronounced. These small etches can also become rough and allow new dirt to adhere to the coin.
Commerical Coin Cleaners
If you go to any coin supply company, you will find commercial coin cleaners. While there are a few that claim to be pH neutral, they contain elements that could cause damage to coins. For metal detector finds and non-rare coins, these may be fine products to use. Others that will brighten or tone a coin do so by altering the surfaces and are not recommended.
Soap is a salt of a fatty acid. Chemically, a salt is a compound that neutralizes the reaction between the alkaline and acid properties of the chemicals. When fats are combined with other ingredients to reduce its acidity, it creates a soap that can be used for cleaning or lubrication. The problem is that the fatty acids on their own will not damage coins, you never know what the alkaline components are that have been added to balance the pH (potential of Hydrogen) of the acid.
Unfortunately, there is no standard definition of pure soap. Its common use is to define a product whose pH is as close to neutral (pH 7) as chemically possible. Unless the company discloses its formula, it would be impossible to tell if the makeup of the soap will negatively interact with the metals.
One final item you should have is distilled water. Distilled water has all the natural impurities removed and reduced the risk of the rinse damaging your coins. Using a squeeze bottle filled with distilled water is the most effective way to rinse away the olive oil or acetone.
When using either olive oil or acetone, the procedure is similar:
- Start with a clean work area. Wash your hands and work on a clean surface. Cleaning your workspace with anti-bacterial wipes will also help. Make sure your work area is safe and well ventilated, especially if you are using acetone.
- Consider covering your work surface with a lint-free towel folded over several times. If you drop the coin, you will drop it on the padding provided by the towel.
- If you are using acetone, don your safety gear. I cannot stress enough that while using acetone is an effective cleaner, you need to work with it in a well-ventilated area and away from any ignition sources, like your kitchen. If you smoke, you may want to leave your matches and lighter outside your work area.
- Pour your acetone or olive oil into a glass that would cover the coin. The depth should be about one-quarter to one-half inch of your liquid. It is also important to use glass for this. Acetone will react with plastic and olive oil may loosen anything that would be stuck to the plastic. A clean glass jar, drinking glass, or dessert bowl works best.
- If you are using acetone, place the coin in the glass and swirl it around for about 30 seconds. After a few swirls, you should start to see dirt in the acetone. If there is PVC on the coin, hopefully, you can see it begin to loosen. Do not do this for much longer than 30 seconds since the dirt in the acetone could scratch the coin.
- If you are using olive oil, place the coin in the glass with the dirtiest side up. Swirl it a few times to ensure the coin is coated and let it sit. Olive oil is not as strong as acetone and needs time to loosen the dirt. Depending on how dirty the coin is, let it sit for 30 minutes to three hours. Do not touch or swirl the coin. Just let it sit.
- Remove the coin from its bath with tongs or your gloved hand. Then using your squeeze bottle filled with distilled water, rinse the coin. Rinse it well to remove the acetone or olive oil. Olive oil is harder to rinse, so patience is required.
After the rinse, place the coin on a lint-free cloth and let it air dry. DO NOT RUB THE COIN! Even though you are using a lint-free cloth, it will scratch the surface. Wait for the coin to dry naturally before storing it away.
If your cleaning attempt did not work, try again. If you used olive oil and want to try again, let the coin sit longer. You may also try using acetone instead. If you used acetone to try to remove PVC damage and it did not work, there is one more thing you can try using a cotton swab:
- After swirling the coin in the acetone, remove the coin from the liquid and place it on a clean surface. Make sure you are using all of your safety precautions.
- Using a cotton swab with a cardboard handle (do not use once with plastic handles since the acetone will react with the plastic), dip the cotton in the acetone and roll the cotton tip across the problem area of the coin. You can gently nudge at PVC particles that may still be attached to your coin. DO NOT RUB THE COIN! You are trying to remove the PVC without causing any further damage and rubbing it or using any other abrasive motion will damage the coin.
- Keep rolling the cotton tip over the area, changing tips after a few rolls. You may also want to have a little clean acetone nearby to dip the cotton swab.
Most importantly, be patient. It may take a few swabs to see results. If it is not working or you feel anxious doing this, then stop. The last thing you want to do is add damage to your collectible. At this point, if the coin is not “clean” then it may not be cleanable. You can try to contact a professional conservation service for additional help.
When you are done, make sure you clean your work area and dispose of your used materials properly. Acetone is considered hazardous so NEVER POUR ACETONE DOWN THE DRAIN. Do not let it sit out because allowing it to evaporate will add toxic vapors in the air. Many cities and towns have hazardous waste processing rules. Find out what they do in your area to allow for disposal of acetone. You can also ask the sales clerk at the store where you bought the acetone for your area’s acceptable disposal options.
While olive oil is not hazardous, it is not a good idea to pour it down the drain. The natural fat in the olive oil will congeal and may stick to your pipes. After a while, the fat builds up and will cause a clog. In my neighborhood, the water company once had to remove a 25-pound congealed ball of grease that caused a backup in everyone’s drain. It was not a pretty sight. You can dispose of olive oil with the trash since it is a natural product and will not pollute the environment.