How Are Coins Made? Blanking, Striking and Fighting Counterfeiters
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A modern mint turns a coil of metal strip into finished coins at rates above seven hundred pieces a minute per press, with every one identical to within a fraction of a gram. The process has four stages that have not changed conceptually since the invention of the screw press, and the engineering effort goes overwhelmingly into two problems: making the design appear in a single blow, and making the result difficult to fake.
From strip to blank
Modern circulating coins are rarely solid precious metal and are usually alloys or clad sandwiches chosen for cost, wear and, increasingly, for how they behave in a vending machine's sensor. Copper-nickel, nickel-brass, steel with a nickel or copper plating, and multi-ply plated steel are all common, and a bimetallic coin with a ring of one alloy around a centre of another is now standard for higher denominations because it is much harder to counterfeit. The metal arrives as coiled strip of precisely controlled thickness, which is fed into a blanking press that punches out discs at high speed, leaving a webbed skeleton that goes straight back for remelting. The blanks are then annealed by heating to soften the metal, cleaned and, critically, passed through an upsetting mill, a machine that rolls each blank between a grooved wheel and a segment to squeeze a raised rim onto the edge. That rim is why coins stack, why they wear on the rim rather than the design, and why the metal flows correctly when struck.
The dies and the strike
The design begins as a sculpted relief far larger than the coin, historically in plaster and now usually as a digital model, which is reduced mechanically or cut directly into steel by computer-controlled engraving. The result is a master punch, from which working dies are made by hubbing, pressing the punch into softened die steel, so that a single original produces many working dies without re-engraving. A coining press holds a fixed lower die, a moving upper die and a collar surrounding the blank, and the strike happens in a single blow of tens to hundreds of tonnes that squeezes the metal to fill both dies at once while the collar contains it sideways and forms the edge. Because the metal has nowhere else to go, the collar is what produces a perfectly round coin of exact diameter, and a collar carrying grooves produces the milled or reeded edge. Dies wear and are replaced after a few hundred thousand strikes, and the small differences between dies are what die-variety collectors spend their lives cataloguing.
The anti-counterfeiting features
Coin security is a quiet arms race, and a modern coin carries more defences than most people notice:
- •A milled or reeded edge, originally introduced to stop clipping, the shaving of precious metal from the rim, and retained because a missing or crude edge is instantly detectable
- •Edge lettering, struck into the rim either by the collar or in a separate operation, which a simple cast copy cannot reproduce cleanly
- •Bimetallic construction, which requires a counterfeiter to join two alloys accurately
- •Precise electromagnetic signature, since vending and sorting machines measure conductivity and permeability rather than looking at the coin, which is why the exact alloy matters more than the design
- •Latent images, where a finely ridged surface shows one design from one angle and another from a different angle
- •Micro-engraved detail too fine to survive casting, and irregular or multi-sided shapes with constant width so they still roll through mechanisms
Why the metal costs more than the coin
The recurring embarrassment of minting is that low denominations can cost more to make than they are worth, a situation described as negative seigniorage, seigniorage being the profit a state makes from the difference between a coin's face value and its production cost. Rising metal prices have repeatedly forced composition changes, which is why the American cent switched from mostly copper to copper-plated zinc in 1982 and why the British penny went from bronze to copper-plated steel in 1992, a change that made pennies magnetic and rendered some existing machines useless. Several countries have simply withdrawn their smallest coins and rounded cash transactions to the nearest five units, including Canada, Australia, New Zealand and much of Scandinavia, with no observable inflationary effect. The longer trend is that coins matter less every year as electronic payment expands, and mints have responded by diversifying into commemorative and bullion issues, which are sold well above face value and are now the profitable part of the business.
The takeaway
Coins are punched as blanks from coiled strip, softened, cleaned, and given a raised rim in an upsetting mill before being struck in a single blow between two dies inside a collar that forms the edge and fixes the diameter. Designs reach the dies through a sculpted relief reduced into steel, with working dies copied from a master punch. Milled edges, edge lettering, bimetallic construction and a precise electromagnetic signature defeat counterfeiting, and rising metal costs have repeatedly forced composition changes or the withdrawal of small denominations.