Up to 1709, furnaces could only use charcoal to produce iron. However wood was becoming expensive as the forests were being cleared for farmland and timber. Although cheap and plentiful, coal wasn't a feasible fuel because it contained sulphur that made the iron too brittle to be of any use. However in 1709, Abraham Darby finally succeeded in smelting iron with coke, and bought his workers beer to celebrate.
This technological achievement allowed a major expansion of the iron trade and ultimately, it helped lead to the Industrial Revolution. In the space of forty years, the valley went from being a small village to a major mining site, employing about 500 people. After 1709, Coalbrookdale saw other achievements such as the first cast-iron bridge that was built over the River Severn and the first cast iron framed building that was built in Shrewsbury.
Here is a list of the terms used on the animation:
cams - rotating pieces of machinery, (made of wood in this case) which help translate rotary motion to linear motion. The cams rotate, and its spokes push the bellows down in a linear motion.
coke - coal which has been heated to burn off oils (impurities) to leave carbon.
crucible - a container at the bottom of an iron furnace where the molten metal collects, made of a substance that can resist the great heat required for melting metals.
iron ore - compounds of iron and oxygen.
pig iron - a crude form of iron which still contains some impurities such as sulphur and carbon, despite the smelting process.
pig bed - a sand bed into which molten iron is poured after the smelting process.
slag - the waste product made up of limestone and silica (impurities in the iron ore), ash, and oxides. It is a mixture which is lighter than the molten iron so it forms a layer above it.
tuyere (pipe) - the nozzle through which an air blast is delivered into the furnace.