They look like plating blisters to me but can they be in a perfect uniform pattern?Or this is something done outside of the mint.
Maybe feom the electroplating process. Looks like moisture may be involved. Hope someone with more knowledge ways in.
Agreed. There was probably just a tiny bend in the plating or maybe a touch of grease or something that weakened or change the bonding process across that path of blisters...clearly this planchet for whatever reason was prone to blistering.
