A question of grey or white: Why Abraham Darby I chose to smelt iron with coke

摘要

The tendency for an iron to solidify white or grey on coming out of a blast furnace in the 17th and 18th centuries is reviewed and quantified. It is demonstrated that iron from a charcoal blastfurnace could not produce the necessary grey iron in a thin-walled cooking pot cast in a cold mould. Charcoal iron masters therefore had to pour their metal into heated moulds, which obliged them to use the costly loam moulding process. Abraham Darby's great breakthrough was realising that iron made with coke could produce a grey iron pot in a cold mould, which allowed him to use the much cheaper green sand process. His patent tells us he realized this several years before moving to Coalbrookdale. Part of the evidence for this assertion involves identifying castings made with each process. A pot in the Ironbridge Gorge Museum is identified as the oldest known coke-iron casting made in the western world.