To retain the value and look of your coin collection, proper care and storing is essential.
Cleaning
While you may be tempted to clean your coins to make them look shiny and new - proceed with caution. Most of the time, cleaning coins reduces their value.
If you absolutely must clean a coin to remove dirt, use good-quality mild soap and water. Once you've washed the coin, pat it dry with a soft towel. Don't brush or rub it, which can scratch the coin's delicate surface. Believe it or not, older coins that show the deep coloration of age are far more desirable than coins whose surfaces have been stripped away by improper cleaning.
Handling Your Collection
To preserve the value and natural condition of your coins, it is important that you handle them carefully. A coin should be held by its edges between the thumb and forefinger. This protects the coin's surface and design from fingerprints and the natural oils on your skin that can be corrosive. Never hold a coin so that your fingers touch the obverse or reverse surface. Doing so can leave fingerprints, which are difficult to remove.
Some experienced coin collectors use soft cotton gloves when handling their uncirculated or proof coins. If you choose not to wear gloves, make sure your hands are clean before handling your coins. Also, hold coins over a soft towel or other soft surface in case you drop them. Finally, don't talk directly over your coins because tiny, almost invisible droplets of saliva can drop onto the coin and show up later as spots. Just like fingerprints, those marks are difficult, if not impossible, to remove.
Storing and Displaying Coins
To keep the value of your collection safe, here are four standards you should follow:
Always store your coins in a place that is consistently cool and dry. Sharp changes in temperature and moisture promote tarnish and spots that will devalue your coins. For instance, don't store your coins in the attic or basement where the temperature can fluctuate significantly.
Keep your coins in their original holders, if at all possible. All modern proof sets and commemoratives should be bought and sold in their original cases and capsules.
Save the Certificate of Authenticity and the information card that comes with United States Mint proof, uncirculated set, and commemorative sets. These items are considered to be part of the set, and if they are missing, your coins will be harder to sell.
As your collection becomes more valuable, you may want to store it in a safe-deposit box. Or, if you choose to keep your collection at home, check with your insurance company to make sure it's covered for the full replacement cost.
Storage Options
Flips are clear plastic holders with two pockets - one for the coin, the other for a label. Some flips, such as those made of Mylar, are good for storing coins but can be a little stiff and brittle. When you put a coin into a flip or take it out, "bow" the flip to avoid scratching the coin - press both edges gently to make a wide opening for the coin.
Soft plastic holders aren't always a better alternative. You definitely want to avoid them if they contain polyvinyl chloride (PVC). This chemical, used to make plastics softer, will take a valuable coin and turn it into a sticky, worthless mess. How? Over time, the sticky film spreads from the container to your coin, eating into its surface. For this reason, it's been nicknamed "green slime."
Other good storage choices include:
2"x2" cardboard holders.
Plastic tubes (ideal for rolls of coins).
Hard plastic holders (preferable for more valuable coins). They are available for individual coins and small sets.
Polyethylene sleeves (good for short-term storage).
Paper envelopes (for circulating coins). Be sure to use envelopes especially made for holding coins, or your coins may change color over time due to reaction with sulfur or other chemicals present in the paper.
Foldout albums, when properly used, offer some protection from wear and handling. However, over several years, coins may tone due to reaction with sulfur or other chemicals in the air. Therefore, these albums are not a good choice for long-term storage of higher-grade coins. Slabs (sonically sealed hard plastic holders for individual coins). They offer good protection, but slabbing coins is an expensive process. For that reason, slabs are generally suitable only for more valuable coins.
