I have been researching plating issues on Copper Plated Zinc Cents. The information I have found has been both interesting and challenging. My research has resulted in some papers I prepared to organize the information in a way that I can understand. Unfortunately, I have only scratched the surface! It seems that I continue to find significant related aspects that I may yet include in future revisions. I am sharing one of those papers here in .pdf format. Click on the link to read. CONCLUSION The average weight of Copper Plated Zinc (CPZ) Proof Cents, compared to the average weight of CPZ Business Strike Cents, along with a permissive Mint Tolerance for Copper Plating Thickness on Proof Cents, and separate specifications for each of the three planchet types in use, suggest that the copper plating on proof cents is at least twice as thick (or more) as the copper plating on business strike cents.
Wow, you really put some work into your project. Thanks for spotlighting an unknown (at least to me) topic.
I don't quite understand this - "Plating Thickness: 0.008 mm + 0.017 mm/-0.003 mm (0.0003 inches +.0007/-.0001 inches)” quoted from the mint. It's supposed to be 0.008mm but can be as high as 0.025mm and as low as 0.005mm? That doesn't make sense.
Probably reflects the tolerances that it's practical to maintain with the particular process that the particular supplier wants to use. Let's not kid ourselves that the specifications for Zincolns reflect anything but the wishes of the winning lobbyists.
Agree. It is confusing! I have received several communications from the Mint RE: tolerances, and their format is inconsistent! I interpret this to mean that thickness tolerance covers the range of 3µ to 17µ. What they left out of their information is what the tolerance is for each planchet type (if any!). I do think their planchet specifications call for a plating thickness of 8µ for BUSINESS STRIKE and 16µ for PROOF STRIKE. Since Mint Tolerance for cent thickness is about ±33%, it may be that is roughly their tolerance for these values, also. Without the documentation they are withholding (general contract substance and summary is available online, but no additional details), this is the best guess I can make! Their mention of 3µ is a mystery, but may just be an outside limit.
Makes me wonder if they mixed the tolerances for proof and business strikes together. Something like business is .008mm, proof is .017mm, and they're both +/- .003mm. Hundredths of millimeters is really tiny though so I can see where there would be a wide variation.
