Abraham Darby and Coke Smelting (1709): Iron at Coalbrookdale

Abraham Darby and coke smelting refers to the breakthrough of 1709, when the Quaker ironmaster Abraham Darby I successfully smelted iron with coke instead of charcoal at Coalbrookdale in Shropshire, England. Coke is a fuel made by heating coal to drive off impurities. By showing that it could replace scarce wood charcoal in the blast furnace, Darby removed a major limit on iron production and laid one of the foundations of the Industrial Revolution.

Background: iron and charcoal

Before the eighteenth century, iron in Europe was smelted in blast furnaces fuelled by charcoal. Charcoal was made by slowly burning wood, so ironworks needed large areas of managed woodland. Fuel was expensive, supplies were uncertain, and furnaces had to be sited near forests. Charcoal is also fragile, which limited how tall a furnace could be before the fuel was crushed under the weight of ore.

Britain had abundant coal, but raw coal contains sulphur and other impurities that make iron brittle. Coal had been coked for brewing malt, and earlier experimenters, including Dud Dudley in the 1620s, had claimed success with coal in iron furnaces, but none established a lasting commercial process.

Abraham Darby I

Abraham Darby was born in 1678 near Dudley, in the West Midlands, into a Quaker family. He served an apprenticeship with a maker of malt mills in Birmingham, where he would have become familiar with coke used for drying malt. Around 1700 he moved to Bristol, where he became involved in brass making and in casting.

In 1707 he took out a patent for casting iron pots in sand moulds, a cheaper way of making the thin-walled cooking pots that were in great demand. To supply his foundry with iron, in 1708 he leased a disused blast furnace at Coalbrookdale, a narrow valley running down to the River Severn.

The breakthrough of 1709

Darby began smelting at Coalbrookdale in 1709 using coke. Local factors helped him. The coal of the area, especially the so-called clod coal, was relatively low in sulphur, and the local iron ore suited the process. The fuel was coked in open heaps before being charged into the furnace with ore and limestone.

The resulting pig iron was well suited to casting, and Darby used it to make pots, kettles and other cast-iron goods. His business prospered, although he did not live to see its full impact: he died at Madeley Court in 1717, aged 38.

Slow spread and the later Darbys

For several decades coke smelting remained rare. Early coke-smelted iron contained more silicon and was less suitable than charcoal iron for conversion into wrought iron at the forge, which was the larger market. The process was therefore mainly used for castings.

Abraham Darby II, the founder’s son, improved the method in the 1750s and produced coke pig iron that forges could use. From then on coke smelting spread rapidly, helped by steam-powered blowing engines and the growth of coal mining. By the late eighteenth century, coke furnaces produced the large majority of British pig iron.

The Coalbrookdale works also cast cylinders and other parts for steam engines, including the Newcomen engine that pumped water from mines. Abraham Darby III, the founder’s grandson, used Coalbrookdale iron to build the Iron Bridge across the Severn, completed in 1779.

Coalbrookdale and the Quaker network

Darby’s success owed much to his religious community. Fellow Quakers in Bristol and elsewhere provided capital and business contacts, and Quaker families such as the Darbys and Reynoldses ran the Coalbrookdale works for generations. Their reputation for honest dealing helped them build trust with customers and partners.

The site itself was well chosen. The Severn Gorge offered coal, iron ore, limestone and clay close together, while the river provided a route for shipping goods to Bristol and beyond. The Old Furnace survives today, enlarged in 1777, inside a protective shelter that forms part of the Ironbridge Gorge Museums.

Myths and facts

Darby invented coke. He did not. Coke was already known and used in malting; his achievement was making it work commercially for smelting iron ore.

Coke smelting transformed industry overnight. In fact it took about half a century to spread widely, and charcoal furnaces continued in use well into the second half of the eighteenth century.

Timeline

• 1678: Abraham Darby I is born near Dudley.
• 1707: Darby patents a method of casting iron pots in sand.
• 1708: He leases the old furnace at Coalbrookdale.
• 1709: Darby smelts iron with coke at Coalbrookdale.
• 1717: Abraham Darby I dies at Madeley Court.
• 1750s: Abraham Darby II produces coke pig iron suitable for forges.
• 1779: The Iron Bridge, built under Abraham Darby III, is completed.
• 1986: Ironbridge Gorge is inscribed as a UNESCO World Heritage Site.

Why it matters

Darby’s success at Coalbrookdale linked iron to coal, Britain’s most abundant energy source. That link made cheap iron possible in quantities that charcoal could never have supplied, enabling the machines, bridges, rails and engines of the Industrial Revolution.