Never, never coins should not be cleaned at all as doing so may end up ruining the coin's numismatic value, coins may lose their brightness over time, and you'll be tempted to polish them. The best advice is ... DON'T. Any cleaning will begin to wear the coin surface, and, though it may look brighter for a time, the coin will lose its value to a collector. The wisest course is to leave your coin collection untouched and stored in the proper holders. The natural tarnish of a coin is expected by collectors, and is actually proof of its authenticity. Never clean touch or rub the surface of any coin. If there is dust on the coin simply blow the dust away gently.
If you decide to clean your coins, here are some pointers to keep in mind to avoid or minimize the chances of damaging them. It is a good idea to consult a coin dealer or other coin expert to assist you in deciding whether cleaning a particular coin is a good idea. When in doubt do not clean a coin. If you decide to clean your coins, Some collectors like to use baking soda as a cleaning method to make a worn coin look shiny and new. This is not recommended as it will generally ruin the numismatic value of a coin.Dirt and grime that accumulates on coins can often be safely removed by applying a layer of Vaseline to both surfaces of the coin with a Q-Tip and then gently rubbing these surfaces clean with a very soft lint free cloth. If you decide to clean your coins, Never use abrasive cleaners such as rubbing alcohol or olive oil to clean coins. If you decide to clean your coins, never use jewelry and metal polishes are usually too harsh. Never, for example use silver tarnish remover to clean silver coins as it will adversely affect a coin's natural toning. If you decide to clean your coins, always rinse the coins with distilled water after cleaning. If you decide to clean your coins, Tap water should not be used as it contains minerals which may create spots on the surface of a coin. Let coin air dry after cleaning never rub a coin dry. If you decide to clean your coins, Soaking a coin in olive oil or mild soapy water is another method that can often safely remove dirt or other substances adhering to a coin.Cleaning or polishing your coins will do more harm than good. Once metal has been exposed to the air, it is natural for it to oxidize, or tone.
Cleaning is not recommended, it almost impossible to find older coins that have not been cleaned. It is lack of experience that causes people to ask if a coin has been cleaned. For example, a Morgan silver dollar that is over one hundred years old, has probably had dozens, if not hundreds of different owners. Coins like the GSA CC Dollars are usually uncleaned because they have been sealed in uncirculated condition. The only sure way to know a coin has not been cleaned is to buy it certified by a reputable certification company like, PCGS, NGC, NTC, ANACS or NNC.