Iron tapped from the blast furnace is pig iron, and contains significant amounts of carbon and silicon. To produce malleable wrought iron, it needs to undergo a further process. In the early modern period, this was carried out in a finery forge. There were several types of finery forges. The dominant type in Sweden was the German forge, which had a single hearth that was used for all processes. In Uppland north of Stockholm and certain adjacent provinces, another kind known as the Walloon forge was used, mainly for the production of a particularly pure kind of iron known as oregrounds iron, which was exported to England to make blister steel. Its purity depended on the use of ore from the Dannemora mine. The Walloon forge was virtually the only kind used in Great Britain. This had two kinds of hearth, the finery and the chafery. In the finery, the finer remelted pig iron so as to oxidise the carbon (and silicon). This produced a lump of iron (with some slag) known as a bloom. This was consolidated using a water-powered hammer (see trip hammer) and returned to the finery. The next stages were undertaken by the hammerman. His work was to draw the bloom out into a bar to produce what was known as bar iron. In the course of doing so, he had to reheat the iron, for which he used the chafery. The fuel in the finery had to be charcoal, because impurities in any mineral fuel would affect the quality of the iron. This is an obsolete process of making iron. The finery forge process began to be replaced from the late 18th century by others, of which puddling was the most successful. These used mineral fuel (coal or coke), and freed the iron industry from its dependence on the speed of growth of trees. That transition is the industrial revolution for the iron industry.
See also
References
- H. Schubert, History of British iron and steel industry c.450 BC to AD 1775 (1957), 272-291
- A. den Ouden, 'The production of wrought iron in finery hearths' Historical Metallurgy 15(2) (1981), 63-87 and 16(1) (1982), 29-33.
- K-G. Hildebrand, Swedish iron in the seventeenth and eighteenth centuries: export industry before industrialization (Stockholm 1992).
- P. King, 'The cartel in oregrounds iron: trading in the raw material for steel during the 18th century' Journal of Industrial History 6 (2003), 25-48.
