For anyone interested in experimenting, it should be rather easy to make a 1943 copper cent. 1. get a BU 1943 steel cent. 2. harden it 3. get a block of steel 4. heat the block cherry red 5. press the hardened cent into the steel block 6. machine the metal away from the outline of the cent to make a die 7. harden the steel die 8. follow the same procedure with the opposite side of the coin 9. get a "copper" cent blank planchet 10. get a steel plate the thickness of a cent and machine a hole to the diameter of the cent 11. put the planchet in the hole in the steel plate and use a hydraulic press to press the dies you made into the cent planchet. 12. repeat as necessary and wait for the Secret Service to show up
Supposedly Hofmann added mintmarks to coins by covering the entire coin except where the mintmark was to be added. Then he plated the coin layer after layer after layer until he had built up a mintmark. When the material covering the coin leaving a coin with a mintmark.