Cleaning old coins is a topic that often divides coin collectors and numismatists. Generally, experts advise against cleaning coins, as doing so not only removes the patina, it can also scratch their surface and will most likely diminish their value, especially for collectible or antique coins.
Coin collectors and numismatists prefer coins with their original, uncleaned surfaces.
However, if you have circulated 90% junk silver coins that you wish to clean for personal enjoyment and are not concerned about their collectible value, there are a variety of gentle methods you can use.
The simplest and least invasive method is to use soap and warm water. Soak the coins in warm water with a mild dish soap like Dawn and then gently rub them with your fingers or a soft cloth. Avoid using any abrasive materials that can scratch the coin.
For coins with heavy buildup, an olive oil soak can sometimes loosen grime over time. Place the coins in a container filled with olive oil and leave them for a week or longer. This method is very slow and can take quite a while to show results.
Vinegar and Salt can be used for cleaning base metal coins such as common modern pennies. Mix vinegar with a teaspoon of salt and soak the coins in the solution for a few minutes before rinsing them thoroughly with distilled water. Be aware that this can potentially damage the coin’s surface and is not recommended for valuable or antique coins.
Electrolysis is often used by professionals and involves passing an electric current through a solution with the coin as an electrode. It can be effective but also risky, and should not be attempted without proper knowledge and equipment.
There are a variety of commercial products in the form of liquids, foams and creams specifically designed for silver cleaning. For really grimy 90% junk silver, cleaning creams like Wrights Silver Cleaner, available from Amazon, often produce excellent results when used with a soft cloth. If you decide to use one of these, follow the instructions carefully.
Several collectors in the Reddit /r/silverbugs forum prefer to clean their junk silver coins with a rock tumbler with surprising results.
If you have old coins that may collectible value, it’s best to consult a professional before attempting any cleaning. Professional conservation involves techniques and substances that are not readily available to the public and is performed by experts with an understanding of the chemistry of coins and the effects of various cleaning methods.
Always test any cleaning method on a coin of little or no value before attempting it on anything more valuable. And remember, if a coin is valuable or if you’re unsure of its value, it’s best to leave the cleaning to the professionals.
