That’s a really nice rim to rim die crack. At least that’s my opinion. For some reason it just doesn’t have the look of a plating blister to me.
However, isn't it strange that all the minor lines in the plating are running parallel to the suspected die crack. That would make me question it.
I call it a rim to rim die crack but I do wonder as it’s copper plated zinc. It just looks more like an die crack to me than a plating blister.
Die cracks are found rarely but they are out there. I searched cuds on coins and did not find any evidence to support my earlier post but I still think I was right. Maybe the die was changed before an actual cud coin was struck.
The ‘crack’ extends through the rim on both sides. This would suggest to me that we are looking at something else.
I read your article and it does seem to fit the description, however I need better pictures to be certain if it is raised or not.
I suspect if it was subsurface corrosion, the linear line would have more more right angle protrusion. The line does seem to go to the edge, but photos do not show enough of the thickness edge of the coin to say it is subsurface or not to me. I still think "crack" at this point. Jim