The following is an excerpt from an article by Stephanie Meredith
Blank. Planchet. Upsetting. Burnishing. You may have heard these words before, but what do they mean? Learn about these terms and explore the seven steps of how the U.S. Mint produces coins and medals.
To review the parts of a coin and the different coin finishes, such as Proof and Uncirculated, read Anatomy of a Coin.
Step One: Die Making
After a coin or medal design is selected and a digital sculpt finalized as described in part one of this series, die making begins the production process.
In the die making process, the Mint makes several generations of hubs and dies. Hubs show a positive image the way the artist created it. Dies are like a photo negative, displaying the design in reverse.
A computer-controlled milling machine cuts the design into the end of a steel cylinder to make the master hub. The master hub is used to make master dies. To make a master die, a press pushes the master hub into another steel cylinder with a cone-shaped end to transfer the image. The master dies make the working hubs. Working hubs then make the working dies that actually strike the coins.
The Philadelphia Mint makes master hubs and dies for all the coins and medals the U.S. Mint produces. The Denver Mint receives master dies from Philadelphia to produce its own working hubs and dies. Both Denver and Philadelphia make working dies for the San Francisco and West Point Mint facilities.
Step Two: Blanking
After die making, the next step is blanking. Blanks are flat metal discs that will eventually become coins or medals. The Mint makes blanks for nickels, dimes, quarters, half dollars, and dollars. For pennies, numismatic and bullion coins, and medals, the Mint buys blanks.
To make blanks, a long coil of metal is fed into a blanking press that punches out the blanks. They have a slightly different diameter but the same thickness as a finished coin.
The blanks are transported to the annealing furnace for the next stage of the process. The scrap metal from the coil is shredded and recycled.
Step Three: Annealing
Blanks are annealed to prepare them for striking. Annealing changes the physical properties of the metal to make it softer and allow it to be shaped without breaking. The annealed blanks will hold the design better during striking.
The annealing furnace heats the blanks to temperatures up to 1,600 degrees Fahrenheit in an oxygen-free environment. The lack of oxygen prevents tarnishing. They are then dropped into a quench tank filled with “slippery” water to quickly lower the temperature. The slippery water is a mix of water, citric acid powder, and lubricants that keep the blanks from sticking together.
Next, a machine lifts the blanks out of the quench tank to drain. The Philadelphia Mint uses a cylindrical machine called a whirlaway that slowly turns as it lifts the blanks from the water. The Denver Mint uses a large scoop called a skip basket. The blanks travel from the quench tank to the washing area.