Iron

node · earth · Shropshire, the Black Country, south Wales, central Scotland

Ore was never the British constraint; fuel was. Smelting iron with charcoal tied output to woodland, and woodland to acreage, which is why British pig-iron production was small and why the country imported bar iron from Sweden and Russia through the early eighteenth century. Two changes released it. Coke smelting, from Coalbrookdale in 1709, put mineral fuel into the blast furnace and unhooked pig iron from the coppice. Puddling and grooved rolling, patented by Henry Cort in the mid-1780s, did the same for the second stage — converting pig iron to malleable wrought iron using a reverberatory furnace in which the coal fire does not touch the metal, and then rolling the bloom into bar in a fraction of the time hammering took. After that, iron becomes cheap enough to be a structural material rather than a specialist one, and everything downstream — machine frames instead of timber ones, rails, boilers, bridges, ships — follows from that price change rather than from any new idea about iron itself.