Why you shouldn't clean your coins

A coin that has never been cleaned still has its original surface. On an unworn coin that surface carries mint luster, the shine left by the way the metal flowed when the coin was struck.

Turn such a coin under a lamp and the light swings around it like the spokes of a wheel. Harsh cleaning smooths the surface, and that shine turns flat.

The darkening on old silver and copper is called toning. It forms naturally over time as the metal reacts with its surroundings, and it is not dirt. Toning runs from pale yellow through blue, gray and brown to black, and copper coins turn from red to brown.

The U.S. Mint tells collectors that older coins with deep age coloration are more desirable than coins whose surfaces have been stripped by improper polishing or cleaning.

NGC and PCGS, another major grading service, both grade coins on a scale from 1 to 70. Major grading services typically give a cleaned coin a “details” grade instead of a regular numeric grade.

The label then describes the amount of wear in words, such as “VF Details” for Very Fine, and notes the problem. On an NGC label the note may read “Cleaned”, or “Improperly Cleaned” on holders from before 2018. PCGS prints a problem code, and 92 means harsh or abrasive cleaning.

Handle your coins as little as you can until someone has looked at them.

• Leave dirt, dark color and spots alone.
• If you need to move a coin, hold it by the edges over a soft towel. Fingerprints on the faces can leave permanent marks, especially on proof and uncirculated coins.
• Leave coins in their albums, flips, holders and Mint packaging, and don't open rolls. Photograph the ends instead.
• Taking coins out can scratch them. The sliding plastic strip in an album can leave a row of fine lines across a coin.
• If a coin was cleaned years ago, leave it as it is now. More cleaning will not bring the surface back.

Leave notes as they are. Don't flatten, press, iron, wash or tape them, and don't try to repair tears.

Pressing takes out the natural wave of the paper and the raised impression left by the serial numbers and seals. Washing fades the colors.

PMG, a grading service for paper money, gives its Exceptional Paper Quality (EPQ) designation only to notes that have not been pressed, washed or repaired. The Library of Congress advises against using self-adhesive tape or glue on paper.