Before you go to town on that dirty coin with the silver polish, find out more about it. Who knows, it could be one of the dollars George Washington supposedly threw across the Potomac (presumably where the river is about five feet wide). Should the coin have his picture on it, that’s generally (no pun intended) a tip off that he didn’t throw that particular one. But it could still be valuable!
Why You Shouldn’t Clean Your Coins
Before you do anything, assess its value. If you can’t look up the coin yourself in the PCGS coin price guide, take it to a reputable coin dealer and ask him whether it’s worth anything. If it is, don’t even think about cleaning it.
Cleaning affects the value of collectible coins, and definitely doesn’t increase them. The patina a coin builds up over the years is part of its total essence, its history, like the patina on old silverware. Remove it, and you can reduce its value by as much as 90%! Collectors value coins with attractive patinas, which actually protect the coin’s surface.
How are Coins Graded?
The way collectors establish the value of a coin is by grading it, an art rather than a science. Grades run from the top grade, a score of 70: “Mint, un-circulated,” which means there is no sign of wear on the coin. The bottom classification is “Basal,” which means “A lump of metal barely identifiable as a coin”. No amount of cleaning or polishing is going to raise a coin from one grade to another. In fact, the two major companies that grade coins, PCGS (Professional Coin Grading Service) and NGC (Numismatic Guarantee Corporation), refuse to grade coins that have been washed and/or polished. It’s the amount of wear and tear on a coin that counts towards its value, not how “pretty” it is.
Should you be a collector or intend to become one with this very coin, you definitely don’t want to clean or polish it unless you have just discovered it with a metal detector and dug it out of the ground. Once any metal has been exposed to the air, it’s going to oxidize, or tone. If you strip the coin of this toning, not only will you lose any remaining mint luster, the coin will appear harsh and unappealing, and it will suffer microscopic abrasions that lower its grade.
For coins that are not particularly valuable, there are only a couple of reasons for washing them. One is when they are going to be incorporated into jewelry and therefore should look nice. The other is to render them less communicable as reservoirs of disease germs. Otherwise, why bother?
How to Clean a Coin
If you’re going to do it, you might as well do it right:
- Handle the coin by the edges to leave no fingerprints. (Not because you stole it, but because fingerprints transfer caustic oils from your fingers to the coin.)
- Avoid abrasives. Commercial coin polish, however, can be used if the coin is not valuable. Toothpaste may also work.
- Run warm water over the coin for about a minute, preferably using water under some pressure.
- Soak the coin from a few hours to a week or two until any deposits disappear. Soak gold coins in hot soapy water.
- Bronze, silver, copper, or nickel coins go in distilled water or olive oil (but, for some reason, not virgin olive oil) to keep from tainting the coins further.
- Tough stains can be removed with white vinegar. Or try soaking silver coins in lemon juice for a few minutes. Others suggest putting the coin in a cup of cola drink, though this is going to leave a sticky residue.
- Always follow any one of these baths by washing the coin in denatured alcohol.
- When soaking, don’t mix different metals together.
- Rinse the coin under very warm water.
- Lightly brush any remaining dirt off the coin with a soft toothbrush and dish soap. Apply little pressure.
- Pat the coin dry with a soft, lint-free cloth, then lay the coin on a soft, dry cloth to finish drying. Do not rub the coin dry.
- Spot-clean encrusted dirt with a toothpick without scratching the surface of the coin.
- Hot sauce can be used to burn some dirt off coins; cola drinks can make them shiny. (Gives you pause about eating a lot of hot sauce or drinking a lot of Coke, doesn’t it?)
How to Remove Mineralization
There is at least one special case where valuable coins should be cleaned: those that have been fished out of the ocean; in other words, salvage booty.
The standard method for removing coral calcification and mineralization from such coins is to clean them in an electrolysis bath. It’s not simple:
- Buy or build an electrolysis bath.
- Mix calcium carbonate (obtained at pool supply stores) one part to 48 parts of distilled water inside an electrolysis unit.
- Avoid running with a high electric current, which will peel away metal from the coin.
- Fix the distance between the anode and cathode poles to avoid having the current take metal off the coin.
- Never leave the coin unattended.
- When done, rinse the coin in clean distilled water.
- After rinsing, and using distilled water – not the stuff you’ve already used, repeat the electrolysis process without the calcium carbonate to remove all traces of the electrolyte from the coin.