If you are not a professionally trained conservator, cleaning ancient coins can be detrimental to their value. Chemicals, residue, water, and physical deterioration can wreak havoc on the surface of a coin. Improper cleaning methods can wash away the details and value that those details impart to the coin.
It is best not to clean rare coins as removing the patina can significantly reduce the value of them. For this reason, most coin hobbyists almost never clean their coins. In fact, 99% of coins do not increase in value after you clean them, but many will be greatly devalued.
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.
To be safe, after cleaning with vinegar or lemon juice, it is best to soak the coin in distilled water with a little baking soda added for a week. (Never use vinegar or lemon juice to clean bronze coins.) Silver coins can also be cleaned by placing them in an aluminum can filled with a baking soda and water mix.
Collectors like coins with eye appeal, which means maintaining an original surface, unhampered by cleaning. It does not mean bright and shiny. Most coins tone or tarnish over time. Patina and oxidation are normal and should not be tampered with.
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.
The abrasive product can leave scratches or hairlines on the coin, as well as destroy the luster of the coin; in many cases a coin that has lost its luster will rarely be worth more than half its original uncleaned value. 3. When a coin is cleaned, it takes on an unnatural color.
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.
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.
So while one may believe it's better to clean up that seemingly filthy, chocolate brown penny or the now rainbow tinted silver coin before listing it for sale, think again. That tarnish is actually increasing the coins' value.
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.
As mentioned before, mechanical cleaning is all about scraping and brushing to clean coins. This is the preferred method to clean any ancient coin and preserve it's patina. In any occasion that you clean an ancient coin, this way is the best way; but there are other methods, as well.
Ultrasonic Cleaners
These coins are cleaned by using distilled water with a small amount of detergent in a special vibrating container. Acid based cleaners will eat away at a coin's surface diminishing its value.
When the copper oxide (the pennies) and the phosphoric acid (the cola) get together in the bath, the acid reacts with the copper oxide on the pennies and dissolves it. That's why the pennies get shiny.
It is primarily the result of oxygen and/or sulfur reacting with the coin's metal. However, the toning process can be accelerated by heat, moisture, and various chemicals in the environment. Some of the most harmful chemicals to coins can be found in cheap coin holders and coin folders.
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.
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.
Add a small amount of water to a tablespoon of baking soda to form a paste. Apply the paste to each coin using an old toothbrush and scrub gently. Rinse the coins to reveal the now-shiny surfaces.
However coins will often have on them built up dirt and grease. This may get into the nooks and crannies of the coin. To remove this type of build up you can use a weak detergent solution with a soft cloth (Clux Wipe or similar will do the trick) to take this material off.
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.