Is there any safe way to clean a coin?

Answer 1

If you are hoping to improve their numismatic value, cleaning of any kind reduces the value of a coin.

So in some short words, the answer is NO, STOP, DON'T. The best way is not to do so at all. Other than brushing off surface dirt with a very soft brush, or rinsing with distilled water and patting until thoroughly dry, the cleaning of coins (if done at all) should be left to professionals.

Done incorrectly, cleaning a coin can drastically reduce its value. If the coin is very badly crudded up but valuable enough to make it worth the investment, e.g. you found it in an archaeological dig, there are professional cleaning technicians who have the tools and knowledge to restore the coin. Such techniques were used to remove 150 years of ocean calcification from the S.S. Pacific hoard, for example.

If it has any possible value as a collectible, the best advice is DON'T clean it. Any abrasive cleaner, no matter how mild, will cause tiny scratches in the surface which will decrease its value to a collector dramatically. Chemical cleaners will alter the surface and give the coin an un-natural look. Some household cleaners will make a coin shiny-new looking when first cleaned but after a few months or years they look worse than before.

However, any surface dirt SHOULD be removed before storing the coin in an airtight holder for preservation. Do this by letting it soak in soap (not detergent) and distilled water. Detergents and tap water usually contain contaminates that may react with the coin. Then use an artist's camel-hair brush to gently sweep away any loosened dirt and let the coin air dry on a soft cloth. If any additional cleaning is required, it should be done by an experienced professional conservator. In fact, most collectors and dealers will pay far less for a coin that's been cleaned than for one that's in its original condition, even if it's dirty. Think of what happens on Antiques Roadshow where someone proudly shows off the cleaning job they did on an old table. Then one of the Keno brothers tells them that they HAD a $20,000 antique, but their "fixing" with turpentine or whatever took its value down to $1,500....

Here is the best solution: DO NOT USE COIN CLEANERS LIKE BRASSO, TARNX, ETC!!!!!!!!Don't use any abrasive substance, or try to clean it by rubbing, scratching, or scraping! If you soak your coins, use distilled water, and you can add a bit of soap. however, the soap solution can damage proof coins or and upper-grade coins with copper in it. For coins that won't be damaged, rinse them thoroughly and air dry. Another solution is to soak a coin in olive oil for several months. The oil will eventually dissolve the crust. However, badly corroded coins have permanent damage inside. The same goes for ancient coins with patina on it. Acetone is usable, but use it in a well ventilated area. You can also use vinegar and let it soak. That will also clean it.

As for Proof coins and Uncirculated coins, don't try to clean them. Get a replacement, or keep it as it is.

Facts from Coin Collecting 101 (Alan Herbert) "If there is any possibility that these coins have any numismatic value, cleaning them will just reduce that value to the amount of silver they contain. They may look good when first cleaned (if you don't use a magnifier), but almost any coin that has been cleaned will look worse in a few years than it looked before the cleaning. Drying with a paper towel will leave hundreds of tiny scratches, destroying the natural surface."

A Different Answer:

Most of the answers given so far concern themselves with any potential damge that may be done to the surface of the coin. Pristine uncirculated coins, proof coins and the such may suffer somewhat from improper cleaning methods, however, a tarnished silver or copper coin has already been damged even before you clean it. Tarnish is corrosion and even on silver it will leave tiny pits in the surface of the metal. The heavier the tarnish, the worse the pitting. This is why when an older coin is cleaned with chemicals the original luster never returns. So by cleaning a coin you probably do a little damage depending upon how you do it but in the end you are simply exposing the damage the tarnish/corrosion has already done. I don't know why so many collectors do not realize a tarnished coin is , in fact, damaged by the tarnish and thus should be worth less than the untarnished coin.