Why Some Coins Have Ridged Edges

Pull a 2-euro coin out of your pocket and run your nail along the edge. Feel those tiny, evenly spaced grooves? They're called reeding, or milling. Now grab a 5-cent piece: the rim is smooth as a river stone. That difference is no engraver's whim. Behind those grooves hides an old war against thieves, and one of the greatest minds who ever lived got mixed up in it.

When shaving a coin paid handsomely

Go back to the days when coins were made of real gold and silver. A coin was worth something not because a state said so, but because it genuinely held its weight in precious metal. The obvious snag: if you quietly scrape a little metal off the edge of a perfectly round, smooth coin, nobody notices a thing. You pass it along as though nothing happened, collect the filings, and melt them down. Repeat across thousands of coins and you grow rich one file-stroke at a time.

This little racket had a name, clipping, and it rotted economies from the inside. The coins in circulation all ended up thin and wasted away, so nobody could tell what a handful of change was actually worth. Merchants weighed coins one by one to avoid being cheated. A nightmare.

Yet the counter-move was elegant: mark the edge. Cut regular grooves or an inscription into the rim, and the faintest touch of a file becomes visible to the naked eye. A clipped coin loses its grooves, so it gives itself away. In England, some coins even carried a motto engraved on the edge, DECUS ET TUTAMEN, "an ornament and a safeguard." The whole policy was spelled out on the very rim of the money.

Newton, Warden of the Mint

Here enters a figure you'd never expect in the numismatics aisle. In 1696, Isaac Newton, already crowned in glory for his theory of gravitation, took the post of Warden of the Royal Mint in London, and became its Master a few years later. You'd picture a quiet sinecure for a tired genius. Wrong.

Newton walked straight into monetary chaos. The Great Recoinage of 1696 aimed to pull the old clipped coins out of circulation and replace them with machine-struck pieces, edges worked and therefore far harder to mutilate. And Newton took the job seriously, to the point of obsession. He hunted counterfeiters like a detective, worked the shady taverns, squeezed his informants, built his case files. His arch-enemy, a forger named William Chaloner, ended up at the end of a rope at Tyburn. The father of modern physics really did send men to the gallows over tampered coins.

Mechanical striking and marked edges won the day. Clipping a machine-made coin without getting caught became nearly impossible, and the game was no longer worth the candle.

Why it survives, even though our coins are worth nothing

Here's the amusing paradox. Today not a single coin in your change holds any gold or silver. They're ordinary alloys, and the number stamped on them has little to do with the metal itself. Clipping makes no sense anymore. And yet the reeding is still there. Why cling to an answer whose question has vanished?

First out of habit and tradition, because a ridged edge remains a reassuring mark of authenticity and one more small hurdle for forgers. Then for the machines: vending machines and coin sorters recognise a coin by its size, its weight and its edge.

But the truly lovely reason lies elsewhere. The grooves help visually impaired people identify coins by touch. Modern currencies deliberately play with edges to make coins distinct. On the euro, each value gets its own rim: the 2-euro coin combines fine reeding with an inscription, the 1-euro alternates smooth and grooved segments, and others carry broad grooves or plain edges. Enough to tell one coin from another without even looking.

The clearest example comes from the United States. The dime and the quarter, once struck in silver, keep their ridged edges. The penny and the nickel never held any precious metal, so their rims stayed smooth. Seventeenth-century logic living on, on coins still rattling around in pockets today.

Next time you're fiddling with your change in a checkout queue, remember that these tiny grooves have crossed three centuries, one scientist obsessed with hunting down forgers, and that today they do a favour for people who read the world with their fingertips. Not bad, for a detail nobody ever notices.