Another major cause of post mint damage (PMD) is cleaning…
Yes, cleaning your coins actually damages them.
While many people think it’s a good thing to clean their “dirty” or old coins, it’s actually one of the worst things you can do.
Cleaning a coin not only alters its natural appearance, but it can also remove a tiny layer of metal from the surface of the coin — forever ruining it. (This is especially true when using abrasives such as toothpaste, baking soda, salt, or even a pencil eraser.)
The bottom line… leave your coins in their natural state. Don’t clean your coins!
What Should You Do With PMD Coins?