Brass castings were traditionally battered into thin plates by hand hammering, but at Baptist Mills the Low Countries' method of water powered mechanical hammers was used. Brass being very malleable it could be beaten into cooking pots and other hollow ware by the same method. There was a large market for these products, in West Africa as part of the evil slave trade, and in the new colonies in the West Indies and America.
The works had a small laboratory, the first metallurgical laboratory in the world, where refinements were made to the smelting and casting processes. Coke had already replaced charcoal in smelting lead and copper in Bristol and Darby introduced coke at Baptist Mills, probably using the brass furnaces to produce the coke from locally mined coal, prior to the brass smelting. John Thomas reported that between 1710 and 1712 the Works was using 250 tons of coal per week. Originally the brass was cast in granite moulds but this was replaced by casting in sand moulds allowing casting of hollow ware in great quantities.
By 1706 Darby had established an iron-making works in Cheese Lane, Bristol where John Thomas eventually succeeded in producing iron pots by casting in a mould of fine sand in a box. Darby patented the process and bound Thomas to keep the secret and work for him alone for 3 years. Darby saw the possibilities of producing hollow ware in iron, equally useful as brass hollow ware, but at much lower cost.
In 1708 Darby leased a derelict furnace at Coalbrookdale in Shropshire where there were local sources of coal and iron ore. The furnace had been constructed by Sir Basil Brooke of Madeley Court in 1638, but he had fallen out of favour in the civil war and died in ther Tower of London
By 1710 Darby had moved all of his interests to Coalbrookdale and was experimenting in smelting iron with various mixtures of fuels. Charcoal was the traditional fuel but this was now in short supply because of deforestation. Using his expertise from the brass trade he eventually succeeded in smelting iron that was not brittle, with coke. The secret was starting with a low sulphur coal and driving off more sulphur by the coking process. He also found that the coke would burn in piles whereas charcoal would only burn in thin layers. By piling the iron ore and coke into a large furnace he could process much greater quantities of ore and a second furnace was built in 1715. His cast iron pots, kettles and bellied cauldrons could be shipped down the Severn to Bristol for export.
The technique of producing cast iron was crucial to the emerging technologies of static steam engines, first developed by Newcomen, and later the railways, so paving the way for the Industrial Revolution.
Darby rented Madeley Court in 1712 whilst having a new home built, but died there in 1717 aged just 39 and was buried in the Quaker graveyard at Broseley. His eldest son Abraham Darby II was just six years old. The Coalbrookdale operations were taken over by other Quaker interests (principally Thomas Goldney of Bristol). Darby's wife died shortly after and the children were educated by their uncle Joshua Sargeant.
At the age of seventeen Abraham Darby II joined the business, in 1738 he became a partner and in 1756 at the age of forty five he was able to buy the whole business. He had improved the quality of pig iron smelted from coke and had expanded the business to national importance before his death in 1763. Control of the business passed to his son in law Richard Reynolds (another Bristolian) because Abraham Darby III was only eleven years old..
Abraham Darby III joined the business in 1768 at the age of eighteen. In addition to his metallurgical interests (he collaborated closely with James Watt and Matthew Boulton) he had farming interests. However he is best remembered for the construction of The Ironbridge opened in 1781.
Back in Bristol, brass making continued at Baptist Mills until 1814. There were other brass works in the area, mostly in the Avon Valley, and production continued into the twentieth century. Zinc smelting was greatly advanced by William Champion and was exploited by John Lysaghts' Iron Works for galvanising. The world's largest zinc smelter was opened at Avonmouth in the 1960s and production continued until recent times.