Up to 1709, furnaces could only use charcoal to produce iron. However, wood (which is what charcoal is made from) was becoming more expensive, as forests were being cleared for farmland and timber.
Coal was a possible alternative to wood, but although it was cheap and plentiful, it wasn't a feasible fuel for making iron, because it contained sulphur, and this made the iron too brittle to be of any use.
However, in 1709, a man called Abraham Darby finally succeeded in smelting iron using coke (see list of terms below) as fuel, and he bought all his workers beer, in celebration of his discovery.
This technological achievement allowed a major expansion of the iron trade, and ultimately it helped lead to the Industrial Revolution. In the space of 40 years, the small village of Coalbrookdale, in Shropshire, where Darby made his discovery, became a major mining site, employing about 500 people.
After 1709, Coalbrookdale saw other achievements, such as the first cast-iron bridge - built over the River Severn - and the first cast-iron framed building - built in Shrewsbury.
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