Quoin: A cornerstone by another name

To most people, a quoin is an architectural term: the external angle of a wall, or a stone or brick that forms that corner. You see quoins on old buildings, often dressed stone that contrasts with the rest of the facade. The word comes from Old French coin, meaning corner, and it has been used in masonry and stonework for centuries.

In letterpress printing, a quoin is something far more urgent and mechanical. It is a tapered metal wedge, usually made of steel, that locks moveable type into a chase (the rectangular steel frame that holds all the type and cuts for a single page). The quoin fits into a groove or space on the chase rim. As the printer tightens it using a quoin key (a long bar that slots into the wedge), the metal is forced outward, pressing the type against the opposite side of the chase with enough force to hold it rigid under the impact of the printing press. Without quoins properly tightened, type would shift mid-print, ruining the impression.

The architectural and printing senses share a visual root: both are about corners or edges, and both involve fitting one piece tightly into another. A quoin in a building is a cornerstone that locks the structure together; a quoin in printing is a wedge that locks type together. But where the mason's quoin is passive and permanent, the printer's quoin is active and temporary. It must be tightened and loosened many times a day, and its grip must be exact.

The printing trade adopted this architectural vocabulary early. By the 16th and 17th centuries, when printing was still a young craft borrowing language from older trades, quoin had already moved from the stonemason's vocabulary into the compositor's. The wedge was seen as serving the same function as a cornerstone: to hold everything in its place. Later printing presses added mechanical quoins and power-driven quoin systems, but the name and the principle remained unchanged.