By Stephanie Meredith
August 26, 2020
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.
Step Four: Washing & Drying
The blanks are washed to restore their original color. The cleaning solution is a mix of cleaning and anti-tarnish agents.
The dryer steam dries the cleaned blanks before they move to the upsetting mill.
Step Five: Upsetting
Upsetting means to “upset” the edge of a coin to create a raised rim. The upsetting mill feeds the blank into a groove slightly narrower than its diameter. This pushes the metal up around the edge to form a rim. The rim protects the final coin from wear and makes it stackable.
A blank with a rim is called a planchet. Some people continue to use ‘blank’ as a general term for a coin before it’s struck.
Proof and uncirculated planchets are placed in a drum with cleaning agents and metal pellets that burnish the surface. Burnishing smooths and polishes the surface. They are rinsed and hand-dried with towels.
Most of the blanks that the Mint buys are planchets ready for striking. When the Mint receives a shipment of planchets, inspectors check them carefully to ensure they meet the required specifications. After that, the planchets either get burnished or, in the case of penny planchets, go directly to the presses for striking.
Step Six: Striking
The Mint has several different kinds of presses for striking coins and medals, but they all work the same way. The press forces the obverse and reverse dies together against the planchet to strike both sides of the coin or medal. Circulating coin presses use from 35 to 100 metric tons of pressure to strike the coins, depending on the denomination. Other presses strike with up to 540 tons of force, the pressure used to create the America the Beautiful Quarters Five-Ounce Coins.
When the dies come together, the planchet metal flows into the shape of the design. A collar placed around the planchet prevents the metal from expanding too much. It also forms the edge design, whether smooth, reeded, or lettered. Dollars receive a smooth edge from the collar, but then go through an additional machine that rolls the lettering onto the edge. Once the planchet receives the design, it is called a coin or medal.
Coins are struck differently depending on their finish. Circulating, uncirculated, and bullion coins are struck once. Proof coins are struck at least twice. And medals, including Congressional Gold Medals, are struck at least once. Larger size medals can be struck as many as four times.
Once the press strikes the coins or medals, they drop into either a bin or a tray. An inspector examines samples for errors. If they pass inspection, they move to packaging. If circulating coins don’t meet certain standards, the batch goes to a machine called a waffler. The waffler bends the coins to form wavy lines before they’re sent for recycling.
Step Seven: Bagging & Packaging
After they pass inspection, circulating coins are counted and weighed. Dimes and quarters fall through a counting machine before they are dumped into bulk storage bags. Pennies and nickels are dropped into the bulk bags without being counted. All the bags are weighed and then stored until they travel to Federal Reserve Banks for distribution around the country.
Robots and automated machines package numismatic coins and medals into blister packs, lenses, and other packaging for sale to the public. The Philadelphia and Denver Mint facilities also package some coins and medals by hand. Bullion coins are packaged in 500-coin monster boxes to ship to authorized dealers.
- How Coins Are Made: The Design and Selection Process goes through how coins are designed and a final design chosen.
- How Coins Are Made: Bringing Coins Into Circulation includes the process the Mint and the Federal Reserve use to get coins into circulation.
- Anatomy of a Coin describes the parts of a coin as well as circulating, uncirculated, and proof finishes.
- Coin Production describes how coins were made from the 18th century to today.
See more Inside the Mint articles.