Guys Check Out The Mint Mark Of This 1986-D Penny!

Can you get a closer shot on the mint mark?

It's corrosion.The copper plating separated from around the MM allowing the environment to start corroding the zinc core. PMD

100% positive, coop has a some great pictures of the MM going through the corrosion process

mmm.. maybe ill clean it with vinegar and see what happens.

Exploded gas bubble. Common.

This is caused by split plating. The air reaches the zinc and it starts to deteriorate. It starts rising first. Sometimes during circulation the contact with coins/etc can flatten the bubble. Then it starts deteriorating in open air and eventually the area keeps getting wider.

If the strike pressure is to strong hard it will cause split plating on the outer devices and columns.



But we see this most often on the mint mark. I feel this is caused in the mint mark punching when the die is prepared. The punch makes a slight fin on the die on the lower part of the mint mark. In the first coins struck with this (How many who know) this punctures the plating. Eventually this fin flattens. The mint marks on the post 1989 coins won't happen as often as the mint mark is part of the design without the fin. Acid accelerates the process. I remember on poster one time drilled a hole through the cent and added acid and it left a shell of copper plating.

That was hilarious, coop. I love it.