I know this is the US forum but I’d love to hear theories on this maple leaf that’s still in the OGP so heat is out as a cause.
The cause is simplicity itself - air and improper storage. Silver, toning dark and sometimes completely black, is the most common toning there is. And it's almost always caused by air, just the air itself is enough. Improper storage merely adds to it and makes it happen faster. What you have to keep in mind is that plastic is air permeable. In other words, air goes right through the face of the plastic that coin is in - causing the toning.
Thought You Might Be Interested My Grandfathers Dog Tags When He Fought In Africa In The Canadian Army. If anyone as any info or history of coins used as dog tags I would be interested in knowing more.
awwww what the heck, i've got the pictures laying around.... besides severe split plating, No idea what's all wrong with it, all kinds of "strange look" to me, mostly missing L in liberty, weak date, odd rubbing look on all the high points of the obverse except where you'd expect it, the rim except the little spot around 9 o'clock ... oh and yeah, also an odd rim on the obverse, maybe a bit of Misaligned obverse die? BadThad's 1990 a few posts above has a better strike I think! It's somewhat circulated, but not for long, the exposed zinc tells that tale.