Just followed the OP's wording and called it zinc rot without thinking.
Of course it can't be zinc rot as British Coins along with Canadian Coins use steel cores.
But as NumisRob stated it is still corrosion.
What would it have chipped of off if it was a die chip?
I have never seen a die chip that looked like a blob.
Edited by JimmyD
08/29/2018 3:45 pm