The blast furnace in earlier times

The furnace top house at Berkinge blast furnace in Forsmark 1792. Oil painting (cropped) by Pehr Hilleström (Jernkontoret's picture collection). 

The blast-furnace technique started being used in Sweden as early as the 12th century. At the beginning of the 1980's a well-preserved ruin of a blast furnace was excavated in Norberg called Lapphyttan which was abandoned in the 14th century. The investigations showed that even older furnaces had been operating at the same site at the end of the 12th century.


The figure above shows what the blast furnace basically looked like from the Middle Ages down to the 1830's. Around 1830 a blast furnace produced 3–4 tonnes of pig iron a day and consumed 100–130 hl charcoal per tonne of pig iron, corresponding to about 1,500–2,000 kg of charcoal per tonne of pig iron. In the mid-17th century Sweden's pig iron production is estimated to have been about 25,000 tonnes a year. The blast furnace was fed from above with iron ore as well as limestone and charcoal. Air-blasts were blown into the lower part of the furnace. This process meant that the iron was reduced from the ore and melted down. The iron that was tapped from the furnace was called crude iron or pig iron and contained 4 per cent carbon. The latter had to be removed from the iron to become forgeable. Initially, this was carried out using one of the so-called wrought iron methods.