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So do you think there is any difference in the plating between "circulating and un-circulating or is the difference in the strike only, like proofs?
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Is there a possibility that the plating for proofs is just a thicker one layer as opposed to being double plated or is that unreasonable to think there are two different plating thicknesses to keep up with?
I think the plating for Proof Cents is thicker than for Business Strike. It makes no sense to be "double plated" -- as in 2 separate immersions in the plating bath, since that would be more labor intensive. It is a simple matter to adjust thickness by changing plating time in the bath and/or current and/or other elements. I think that the plating on Proof Cents is twice as thick as on Business Strike Cents. I have not studied the third planchet type of Uncirculated, so I cannot comment about them.