Crucible Cast Steel by the Huntsman Process — Remelting Blister Steel into Flawless Ingots

Blister steel was a triumph, but it had a flaw: its carbon was uneven, rich at the surface of each bar and poor in the core. For fine springs, watch parts, and razors, smiths needed steel that was the same all the way through. In 1740 the Sheffield clockmaker Benjamin Huntsman found the answer — melt the steel completely.

No furnace of the day could melt steel, so Huntsman built one that could. He broke blister steel into small pieces, sealed them in a covered clay crucible, and drove a coke fire hot enough — around 1600 degrees Celsius — to turn the solid steel into a clear liquid. Fully molten, the carbon spread perfectly evenly through the metal and the impurities floated off as slag. Poured into a mould, it set into a flawless ingot of cast steel.

Huntsman's crucible steel was the finest in the world and made Sheffield the steel capital of the age. The principle — melt it to make it uniform — is the same one that still underlies steelmaking today, and it sits at the very top of the iron-and-steel chain that runs from ore to coke to pig iron to wrought iron to blister steel to this.