The U.S. Mint makes the nation’s circulating coins, as well as bullion and numismatic (collector) coins. The Mint’s four production facilities in Philadelphia, Denver, San Francisco, and West Point use a variety of machines and processes. Explore the steps of how the Mint makes coins.
To review the parts of a coin and the different coin finishes, such as proof and uncirculated, read Anatomy of a Coin.
Once the Secretary of the Treasury approves a design, Mint medallic artists transform a line drawing into a three-dimensional sculpt. Once the sculpt is finalized and digitized, the Mint makes coin dies to stamp the design onto the coins.
Step One: Blanking
Blanks are flat metal discs that will eventually become coins. The Mint makes blanks for:
- Half dollars
For pennies, numismatic coins, and bullion coins, the Mint buys blanks.
To make blanks, the Mint buys coils of metal 1,500 feet long made to the correct specifications of each denomination. The coil is fed through a machine that straightens out the curves and then into a blanking press, which punches out the blanks like a cookie cutter. 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, called webbing, is shredded and recycled.
Step Two: 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 Three: 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 Four: 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.
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, penny planchets go directly to the presses for striking.
Special proof and uncirculated planchets go through a cleaning process called burnishing. They are placed in a drum with cleaning agents and small metal pellets to smooth and polish the surface. They are then rinsed and hand-dried with towels.
Step Five: Striking
The planchets travel to the coin presses for striking the design. The Mint has several different kinds of presses, 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 at once. 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 Five Ounce Silver 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 becomes a coin.
Coins are struck differently depending on their finish. Circulating, uncirculated, and bullion coins are struck once. Proof coins are struck at least twice.
Once the press strikes the coins, 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 Six: 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 into blister packs, lenses, and other packaging for sale to the public. The Philadelphia and Denver Mint facilities also package some coins by hand. Bullion coins are packaged in 500-coin monster boxes to ship to authorized dealers.