Plating issue. Zinc Rot issue as stated. Recognized as Post strike damage http://www.error-ref.com/?s=Zinc+rot Not a Mint Error
I disagree, the link provided was informative, but does not explain the shape of the damage. The MM is intact, the damage is mostly separate and forms a shape exactly that of a MM. If it weren’t for the fact that there is a second area doing the exact same thing, I would believe your answers were correct. So the question wasn’t asking what caused the damage but why is it shaped as a MM.
No one can explain the shape of a stain. No two stains are alike. The metal that is affected tones and we have no control over it and it can't be explained. We see what we want to see, usually it's something that's not really there.
What you are seeing is the result of a 8 micron thin copper plating over a zinc planchet. fyi, 8 microns is 0.000314961 of an inch or 0.0080000094 mm. The lower part of the MM, the copper was stretched and created a split plating. Since the zinc is now exposed .... well, it corrodes like steel does under paint when exposed to as simple things as going through a washer/dryer scenario. you can see the split plating if you look closely enough You can see the start of "bubbling" occurring. the "shape of the damage" is directly related to the size of the split plating and the exact handling of the coin over it's lifespan so far. Every coin won't be *exactly* the same because it is corrosion damage, and not a mint error based on a repeatable process. you are seeing the beginning stages of the below images. this is the outcome, sooner or later. more general info https://www.coinworld.com/news/us-coins/2016/08/unexpected-bumps-on-coins-surfaces-vary.all.html
btw, you seem to support that the stain is damage. but as shown, the MM is part of the damage - the lower bottom and right of the MM is damaged from split plating. it looks like it also took a hit on the left part of the D it has a bubble in the middle the split plating is butted right up against it there's a bubble occurring to the left and below going to the right of the MM The MM is not intact. The "shape" of the stain/corrosion is based upon what one convinces oneself that it looks like.
I see what you think is a "D" rotated 90 degrees CW at the bottom of the mint mark. But in the minting process there is no way that would happen. Sorry, it is an illusion and not a mint error.
Yes, what other have said before me is correct. Split plating beneath the mintmark formed into zinc rot. Check this page out: http://www.error-ref.com/split-peeling-plating/
I have read otherwise about Mintmarks being punched incorrectly, even upside down. Seems like the shape of the secondary Mintmarks is not a coincidence. There is also another location below with the same error/damage/illusion or whatever people choose to call it. More than one location means there is something else going on that correlates with the Mintmark somehow. Thanks for noticing the 90° rotation in question. I purposely don’t provide details, so that I don’t influence opinions to much. I don’t believe illusion is the answer here. Thanks for your reply
unfortunately it was the hand punching that probably caused the split plating. A bit too deep, and the thin copper stretched too far and split. I saw the "dangling D" ... but ... you can send it in to attribution. https://www.pcgs.com/submissionguide here's NGC https://www.ngccoin.com/resources/pdf/ngc-ncs-fillable-pdf-instructions.pdf ANACS https://www.anacs.com/PDFFiles/submissionform.pdf ICG https://www.icgcoin.com/submission-form/
