You may have seen this piece of advice on Mullen Coins’ Evaluations page:

The single biggest mistake you can make as a collector: Cleaning your coins. Your collection will likely be worth much less if the coins have been cleaned! An uncirculated coin that has been cleaned is not longer an uncirculated coin! Please do not clean them! The occasional exception to this rule would be a rare coin in heavily circulated condition that has dirt of PVC... in that case professional restoration might be an option.

Have you wondered why that is? Some collectible items such as antique cars can be repaired or restored and can be worth more money if you repair and clean them up. That is not normally the case with coins, though. We’ll go over the reasons here.  

Patina

One reason to avoid cleaning your coins is that natural patina is valuable. Patina is defined as: “a film or incrustation, usually green, produced by oxidation on the surface of old bronze and often esteemed as being of ornamental value.”

Coins oxidize in different ways because the metals they are made of vary. Copper coins typically become light brown to deep chocolate brown over time. Silver coins become light gray to deep brownish gray, darker in the recessed parts of the coin. Nickel coins will turn soft to dark gray, and gold will yellow over time. Of all these metals, gold is the least reactive and will change the least in appearance as it ages and is exposed to air. 

Anyone who has cleaned silverware knows that it’s simple to remove oxidation from metal, but  believe it or not, that simple act can permanently change the appearance of the coin under magnification. This affects its value permanently because serious coin collectors prefer the natural appearance of an old coin over one that’s been artificially restored.  

What Coin Collectors Look For

Coin collectors want pristine, never-been-handled coins or the closest approximation to that that they can get. Uncirculated coins are far preferable to circulated and untouched, uncirculated coins are the most valuable of all. This is because anything that touches a coin has the potential to damage it at the microscopic level. The more abrasive a cleaner is used to clean the coin, the more likely it is to remove the upper surface of the coin - damage that can never be undone.

Luster

When a coin is minted, the metal flows into the recesses of the coin die at extremely high pressure. The result of this is known as mint luster. This is the beautiful shine that a new, untouched coin has. It’s caused by flow lines. Flow lines are microscopic patterns in the metal set by the die. The smaller the coin is, the harder it is to see the flow lines, but they’re there.

When people clean coins, the condition of those flow lines is damaged, and the luster is lost. Put under a magnifying glass, the coin will show scratches marring the surface of the coin. 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.

The bottom line for anyone looking to sell coins from a coin collection: don’t clean your coins. Don’t have them cleaned. A trusted coin expert will know how to value them correctly. If you want the best price for your coins, leave them in the state they are in. Do not to touch them any more than they’ve already been touched. If you would like any other advice about what to do with your coins, please call us at Grand Rapids Coins. We would be more than glad to help you.