Smithsonian Pattern Of The Month/Week/Whatever

Galvano for Schoolgirl Dollar Pattern from 1879

"When final approval [of a design] is received, another negative is prepared. They use this to make a copper electrotype or galvano. The negative plaster cast is dried thoroughly and treated with hot beeswax and powdered copper. Finally, they attach a conductor and suspend the treated model in a copper electroplating tank. This process deposits a layer of copper that is at least 1/16th of an inch thick on the negative model. The resulting copper shell, called a galvano, is separated from the plaster and trimmed. After eliminating all defects from the galvano, the engravers add lead to the back to strengthen it."

"They then mount the completed galvano on a Janvier transfer engraving machine. This machine cuts the design in a soft tool steel blank that is the exact size of the finished coin. This produces a positive replica called a hub. The hub is then heat-treated to harden it. It is then placed on a hydraulic press to prepare a master die, which must then harden."



Image courtesy of Smithsonian Institution, Numismatic Collection. Explanation of creation of master dies courtesy of US Department of the Treasury website (http://www.treas.gov/education/fact...dies.shtml).