This is a good place to start, “Don’t clean your coins.” If you don’t learn anything else from this section, this rule should be it.
There are two types of cleaning for coins, often confused with each other.
Destructive cleaning uses abrasives or acids to clean (and alter) the coin surfaces. Non-destructive cleaning uses solvents that are harmless to the coin’s metal, whether that coin be silver, gold, or modern clad composition.
Destructive coin cleaning will reduce the collector value as much as 50 percent or even more. An expert can, in some cases, improve the value of an old coin by cleaning, but for the average collector the risk of damage is too great, as almost anything you do is going to cut the value. Unless you are an experienced specialist, the answer to “how do I clean my coins?” is, quite simply, “don’t clean them.” The typical response from people who don’t take advice kindly is “I’ll do as I please with my coins and you can go jump in the lake!” Have a nice swim.
Some collectors insist on cleaning their coins. One such collector had thousands of silver dollars. Every coin had been scrubbed with a harsh abrasive, every coin he bought got the same treatment, despite warnings from friends and dealers he did business with. The result, after he was done cleaning the silver coins, the only value left was the silver content, less than an ounce in each coin.
The metal cleaners you see offered for sale on TV and elsewhere all are acid-based cleaners. They remove some of the surface metal in the process of cleaning a coin. Avoid such coin cleaning products at all costs. Even a modern clad coin cleaned with one of these products will lose value. Ancient coins, or gold and silver coins will lose collector’s value, and precious metal content through use of such cleaners.
A weak soap (not detergent) solution in distilled water will remove dirt and grease from an encrusted coin without damaging it, even if the coin is one of those grimy specimens found at the beach.
City tap water has chlorine in it, which will discolor the coin. Use distilled water, and rinse with distilled water. Acetone is another commonly used solvent, but there is a fire hazard that you should be aware of when using it as a coin cleaning material. Fingernail polish remover contains acetone, but it has other chemicals that may cause damage to upper grade coins.
Also this warning: There is no safe method available to clean your upper grade uncirculated or proof coins or copper alloy coins. Always seek professional help and advice concerning these valuable coins.
After using solvents, it’s important to rinse the coins with distilled water, and then either allow them to air dry, or pat them dry. Never rub, even with the softest cloth.
Heavily encrusted coins can be soaked for several months in olive oil. The oil won’t damage the coin further, but it will eventually dissolve the crust. Generally speaking though, trying to restore badly corroded coins is a waste of time. Even if you successfully remove the corrosion, there is usually permanent damage underneath, leaving you with a near worthless coin. The same applies to the patina on ancient coins, which in some cases can actually contribute to a coin’s value.
Guide to Coin Collecting – Index