How Coins Are Made
From artist's design to struck coin: hubs and dies, blanks and planchets, annealing and upsetting, striking, mintmarks, and how worn dies set the stage for errors and varieties.
From design to die: hubs and dies
In plain English
A coin starts as an artist's design. That design is turned into a 'hub' (a steel tool with the design raised up, like the finished coin), which is pressed into soft steel to create a 'die' (the stamp that strikes coins, with the design sunk in and reversed).
Going deeper
The U.S. Mint uses a multi-step chain, master hub to master die to working hub to working die, so the original design is preserved as working dies wear out. Because a hub is a positive image and a die is a negative one, a misalignment while making a die can impress the design twice, slightly offset: the origin of a doubled die.
Sources: United States Mint · Numismatic Guaranty Company (NGC)
Evidence pages
From metal to planchet
In plain English
Coins are struck on round metal discs. A disc punched from a metal strip is first a 'blank'; it's softened by heat, then rolled through a mill that raises a rim, and only then, with its rim, is it called a 'planchet,' ready to be struck.
Going deeper
The blank is annealed (heated to soften the metal so it strikes cleanly) and run through the upsetting mill, which raises the rim that aids metal flow during striking and protects the design from wear. Flaws in the planchet metal cause errors like laminations and clips.
Sources: United States Mint
Striking the coin: business strikes and proofs
In plain English
Most coins are 'business strikes', struck once on an ordinary planchet for everyday use. 'Proof' coins are made differently: polished blanks struck more than once with polished dies, for collectors. Proof is a method of manufacture, not a grade.
Going deeper
A single blow at production speed makes a circulation coin; proofs are struck at least twice at higher pressure and slower speed with specially prepared dies, yielding sharper detail and mirror-like fields (often with frosted, cameo devices).
Sources: United States Mint · Professional Coin Grading Service (PCGS)
Mintmarks: where a coin was made
In plain English
A small letter on a coin tells you which Mint made it: D for Denver, S for San Francisco, P for Philadelphia, W for West Point, and the historic CC for Carson City. Philadelphia left many coins with no mintmark at all.
Going deeper
Mintmark style and position are central to attribution and to spotting added- or removed-mintmark fakes and repunched mintmarks. How and where mintmarks were applied changed over the Mint's history.
Sources: United States Mint
Evidence pages
Dies wear out, and leave clues
In plain English
Dies don't last forever. As they age they can crack, clash (when two dies strike each other with no blank between them), and get polished to clean them up. These leave tell-tale raised lines and marks on the coins they strike.
Going deeper
Die state, the point in a die's life, lets specialists sequence coins and attribute varieties. Polishing imparts fine raised lines; cracks print as raised lines; clashes transfer ghost images of the opposite die. None of these is post-mint damage.
Sources: United States Mint · Numismatic Guaranty Company (NGC)
Evidence pages
Errors versus varieties (a bridge to the next lesson)
In plain English
Two different things can make a coin unusual: a one-time machine mistake (an 'error') or a repeatable quirk cut into the die itself (a 'variety') that appears on every coin that die strikes.
Going deeper
Errors are manufacturing/striking malfunctions affecting individual coins; varieties are die features reproduced across many coins. A doubled die is a variety; a misfed, off-center strike is an error. The next lesson covers both in depth.
Sources: Professional Coin Grading Service (PCGS) · Numismatic Guaranty Company (NGC)
Key terms in this lesson
Hub · Die · Planchet · Annealing · Upsetting Mill · Mintmark · Proof · Business Strike (Circulation Strike) · Die State · Die Polishing · Doubled Die · Mint Error vs. Variety