Abraham's great-grandmother was the sister of Dud Dudley, who was also an illegitimate child of Sutton's, and who had a claim to be the first Englishman to smelt iron using coke as a fuel. Unfortunately, the iron that Dudley produced was not of good quality but knowledge of his (twice removed) cousin's partial success, two generations earlier, is likely to have inspired Darby to perfect this novel method of smelting.
Darby was apprenticed in Birmingham to Jonathan Freeth, a malt mill maker and fellow Quaker. Freeth encouraged Darby to be an active member in the Society of Friends, and he remained so all his life. In 1699, when he completed his apprenticeship, he married Mary Sergeant (1678-1718) and moved to Bristol, where he set himself up as a malt mill maker. Abraham and Mary were to have ten children, of whom four survived into adulthood. The eldest, also named Abraham, was destined to take over his fathers company, when he came of age.
At that time every household would have a brass cooking pot. These were imported from Holland and were so expensive that they were passed down from one generation to another. Darby decided to manufacture these in England, and in 1704 he visited Holland to study production methods and also to recruit some Dutch craftsmen. He returned to establish the Cheese Lane Foundry in Baptist Mills together with his previous partners. He began producing brass pots, but these proved to be too expensive, so he decided to try casting iron pots instead. However the technical difficulties of casting iron pots were too great for Darby. A young Welsh employee, John Thomas, solved the problem by using pure dry sand for the mould, with a special casting box and core. Using this casting method Darby could cast pots of sufficient thinness and lightness. Darby took out a patent on the new casting method in 1707, so that he had a virtual monopoly in the trade.
At this point Darby had a difference of opinion with his partners, who wanted him to concentrate his energies on brass founding. Darby decided to leave the company and pursue his iron founding pursuits elsewhere. In 1708 he left Bristol to establish an ironworks at Coalbrookdale in Shropshire.
During his experiments in iron smelting at the Cheese Lane Foundry, Darby had used charcoal, but it appears that he became convinced that it would be possible to use coke instead. Darby was experienced in the use of coke in malting kilns and he believed that by altering the internal proportions of the blast furnace and providing an adequate blast of air, coke could be successfully used as a fuel. At the time the best coal for coking was that mined in Shropshire, so it was to there that Darby transferred his business.
There had been a blast furnace in Coalbrookdale since 1638, using charcoal as fuel, but it had been partially destroyed by an explosion, and had not been repaired. Darby took up the lease of the blast furnace and rented a house nearby. He also brought workmen with him from the Bristol foundry. They immediately began rebuilding the damaged furnace.
The furnace was used for the first time on 10th January 1709 and the blast appears to have been successful. Darby was probably helped by the fact that the Shropshire coal that he was using was fairly sulphur-free. Another advantage of using coke as fuel was that it did not have to be carefully placed in layers between the iron ore as charcoal had to be, thus saving on time and labour in setting up the blast. Some of the molten iron from the blast was run into pigs to produce ingots for shipment to the Bristol foundry, whilst some was run into moulds to produce pots and other implements. This first blast was followed by others and the furnace continued to churn out implements that were sold locally.
The iron produced by Darby was of good enough quality to be used in forges to make wrought iron, but there was a belief in the trade at that time that iron produced by coke would contain too many impurities. Therefore Darby concentrated on making castings and expanding his business. In 1712 Darby offered to instruct William Rawlinson, a fellow Quaker and ironmaster, in the techniques of smelting with coke. Apparently, Rawlinson, the founder of the Backbarrow Iron Company in Furness, declined the offer.
Production from Darby’s blast furnace increased until, in 1715, he decided to build a second, larger blast furnace. This had a capacity of twelve tons of iron per week compared with five to seven tons for the old furnace. It is not clear whether this furnace began production before Darby’s death.
Darby’s son, Abraham Darby II was only six years old, so until 1745, Darby’s son-in-law and partner, Richard Ford managed the Coalbrookdale works.
Richard Ford, Darby’s son-in-law introduced horse-driven pumps to return water to the furnace pools in dry seasons. Abraham Darby II replaced the horse-driven pumps with a steam, pumping engine. Similarly a steam driven blowing engine was introduced to provide the blast.