Acid Or Corrosive Coin Damage
Coin subjected to acid will obtain a myriad of metal actions, but the most prevalent will be a grainy or etched surface. Acidic substances literally erode away the original surface and how deep the erosion depends on how long the coin was subjected to the substance.

This PMD is often found amongst circulated coins and were just an experiment to see what it would do to coin. Also, the coins used are common and often worth only face value.
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