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The Iron Industry
This page introduces a series of articles about the local iron industry
Introduction to iron
This shows a bloomery furnace reconstructed by GeoArch for the Four Parishes Heritage Group. It was fired in July 2007 at the Severn Valley Country Park
Ironstone is found locally, both in the Wyre Forest Coalfield (especially in the parishes of Billingsley and Neen Savage) and also on the Titterstone and Brown Clees. There is evidence for iron production from medieval times to the 19th Century.
Ironstone contains iron chemically combined with other elements, normally carbon and oxygen in the form of iron carbonate (the mineral form is known as siderite). It occurs in bands in the local coal measures between coal, clay and shale. To produce metallic iron, the ironstone was first heated in heaps to drive off carbon dioxide, a process known as roasting. It was then heated with carbon; the carbon reacted with the remaining oxygen to form ultimately carbon dioxide to leave behind iron.
Iron was first made in furnaces known as bloomeries. The roasted iron would be mixed with charcoal and put in a cylindrical clay furnace, a few feet high and one or two feet in diameter. The charcoal would be lit and hand operated bellows would provide a blast of air to encourage burning. The temperature would reach around 1100 C. This was hot enough to allow the charcoal to react with the ore to liberate iron; any impurities in the ore would melt at this temperature and form a liquid slag which could be run off. However, the iron remained as a solid, spongy mass. It would be removed as a lump from the furnace, reheated and hammered to consolidate the lump into a bar which was then ready for use by blacksmiths. In the later medieval period the process was mechanised; water wheels were used to power both bellows and the hammers.
In the early 1490s the blast furnace was introduced into south-east England from the continent. This was a much larger, taller structure than the bloomery. As a consequence, with large, water-powered bellows, it was possible to reach a temperature of around 1600 C. This was sufficient to melt the iron. The larger size of the blast furnace meant that it could produce far more iron than could be made in a bloomery; the liquid iron could also be poured into moulds to produce objects made from cast iron. Unfortunately cast iron is very brittle due to dissolved carbon. As a consequence, the iron bars made in a blast furnace (pig iron) needed to be remelted in a furnace where it was refined to reduce the carbon content. This gave wrought iron. Initially the refining involved two stages, conducted at forges known as fineries and chafferies.
In the 17th Century there were various experiments to use coal or coke rather than charcoal in the blast furnace. The first commercially successful use of coke was by Abraham Darby in 1709. However, it was not until the middle of the 18th Century that it became possible to make iron from coke that could be converted to wrought iron, the most useful form of the material. Throughout the 18th Century there were also developments in furnace technology, allowing use of coal. In potting and stamping the pig iron was heated in clay pots to keep it separate from the coal. This process was superseded by puddling, in which the iron was melted in hearth separate from the coal fire and stirred, to burn out the excess carbon. However, for some uses, charcoal-made wrought iron remained the material of choice well into the 19th Century.
The availability of large quantities of cast iron encouraged the growth of specialist foundries, where it was remelted to make castings for machines or domestic objects such as cauldrons or irons. The foundries were often found in towns.
Further Reading
The links below will take you to two recent PhD theses which have much information on the iron industry in Shropshire.
"The Iron Trade in England and Wales 1500-1815: the charcoal iron industry and its transition to coke" is the work of Dr Peter King (University of Wolverhampton, 2003).
"The Shropshire wrought-iron industry c1600-1900: a study of technological change" is by Dr Richard Hayman (University of Birmingham, 2004)
Related Links on other Websites
- The Iron Trade in England and Wales 1500-1815: the charcoal iron industry and its transition to coke
- The Shropshire wrought-iron industry c1600-1900: a study of technological change