Cleaning products will remove the lustre and will add tiny scratches and fibres that render the coin worthless. Your numismatic treasure may as well be a blank. If you're worried about your coin's condition, contact a professional coin dealer or conservator for advice.
Even touching the coins introduces oil and dirt to the coin's surface. Since oil and dirt cannot be removed without cleaning, a small touch can cut a coin's value in half or even more because, again, numismatists would rather have an oxidized but untouched coin than a shiny but damaged one.
Don't clean your coins
Many people seem to think they should clean their coins to make them “look pretty” before selling them. This is done with the motive of trying to make more money on the sale. Yet this actually makes the coins worth less.
While you may be tempted to polish your coins to make them look shiny and new, proceed with caution. Polishing and/or cleaning coins can reduce their value. Older coins that show deep age coloration are more desirable than coins whose surfaces have been stripped away by improper polishing or cleaning.
Judge the age and consistency of the color, its depth and evenness. The underlying luster should be undisturbed and in a perfect cartwheel pattern, this being especially visible about the obverse stars. Look for hairlines or other imperfections that may indicate the coin was cleaned at some time in its past.
I would personally say that under $500, you can expect anywhere from 25%-50% of the coins value to be lost due to cleaning. Over $500, I think most professionals will take >=50% of the coins value. How do I know what coins are valuable when going through a big jar of coins?
Travers also wrote that the idea of enhancing a coin's value through cleaning is a misconception. Kenneth Bressett and A. Kosoff also wrote opinions on the matter saying that once a coin has been "stripped" of its original surface and luster, it can "never be fully restored or made Uncirculated again".
Never use metal polish or acid dip to clean your coins! Using these chemicals will cause abrasions or chemical reactions with the metal, permanently damaging your coin.
You should never store coins loose in a box or bag. As the coins rub against one another, they create wear. This is damaging to the edges and higher surfaces of coins, and it will reduce the value of your coins. Instead, each coin should be in a dedicated spot in a folder or album or in its own sleeve or box.
Make sure your coins have been cleared of all dirt, debris and other objects prior to visiting the kiosk to ensure a successful transaction. Items like food, screws, dirty or sticky coins and other objects will jam the machine. Click here for a list of unacceptable items.
Silver coins will acquire natural toning over time. In the realm of coin collecting, the general rule of thumb is to simply not clean your coins, period. Cleaning a coin can impair its surface and hamper its appearance, causing the coin to lose a significant amount of its collectible value and monetary worth.
Before cleaning old coins, consider that appraisers and coin experts suggest not cleaning collectible coins yourself because the coins may lose their value.
Contaminated Coin Procedures
The Federal Reserve does not accept deposits of Contaminated Coin. Customers who wish to deposit coin after decontamination should contact their FedCash Services contact.
A Ziploc bag or other plastic bag will most certainly contain some PVC, as do most inferior grade plastic products. A few years down the road, readers of this article who have followed Higdon's advice and used a baggie to store their coins may find their coins irrepairably damaged and much less valuable as a result.
Storing your coins in paper envelopes or in cardboard boxes is a good way to damage them unless you are careful to use acid-free paper materials. Over time, the paper breaks down, releasing acidic chemicals into the air around your coins.
Bedroom/ Den: When storing your coin collection in your home, you must keep them in a room that does not have extreme temperatures or humidity. The bedroom or a den is usually the safest place because these areas tend to have a comfortable temperature and humidity level.
Vinegar and Salt
Mix vinegar with salt. Place pennies in the solution and let them sit for a while, and then use a clean, soft toothbrush to clean any dirty areas. Rinse the coins, and then polish them with baking soda paste.
Soak coins in warm water mixed with liquid dish detergent to clean off light dirt and grime. Wash each coin gently with a soft toothbrush before rinsing and drying it. Scrub low-value coins with baking soda and vinegar, lemon juice and salt, or ketchup to break apart tarnish.
This method involves the use of high-frequency sound waves to remove dirt, grime, and other contaminants from the surface of coins without damaging them. Ultrasonic cleaning is widely used by coin collectors, numismatists, and museums to restore the luster and shine of old and valuable coins.
Cleaning Coins with an Ultrasonic Device
Not infrequently, the actual value of old coins lies in said patina. So if you have extraordinarily old and valuable coins, you should refrain from cleaning them in an ultrasonic bath.