Coke is formed by heating suitable coal under partially reducing conditions to drive off the volatile components and reduce the sulphur content. Initially, coke was produced in clamps in manner a very similar to that of charcoal, but later retorts were used so that the gas evolved could be used to heat other parts of the processes involved.
The change from the use of charcoal to coke in iron smelting, pioneered by Abraham Darby at Coalbrookdale after possible experimental work in the Bristol brass industry, was important one of the essential steps of the industrial revolution.