Iron production started about 3500 years ago in Asia Minor. In Norway, people have been producing iron for at least 2300 years.
     Arne Espelund, a professor emeritus and a mining engineer at the Norwegian University of Science and Technology, works across multiple disciplines, using chemical analysis to explain how our ancestors produced malleable and cast iron.
     In 1982, Espelund was part of the team that discovered the 2000-year-old iron production facility at Heglesvollen, about 500 kilometres north of Oslo. The researchers found a total of 96 tonnes of slag, spread equally between four furnaces. This suggests that the furnaces operated simultaneously, but in different stages of production. It is quite common to find four ovens beside each other, and there is always water in front of the ovens. "We estimate that teams of about 10 people worked together," says Espelund. "We are talking about a well-planned production process and an industrial enterprise with periodic, batch operation of all the furnaces."
     Ore for iron production was gathered in marshes in the springtime, and smelting took place in autumn. Around 400 places in central Norway alone show traces of early iron production. "Today it's the slag heaps we find first," says Espelund, who has studied slag from Norway, Sweden, Iceland, Austria, and Catalonia, and found similarities.
     People involved in iron-making must have been highly specialised workers, taken out of other useful work to produce iron in the summer months. The iron was important, and of high quality. "A lot of this iron contains about 0.2 percent carbon. That's on par with the best iron a blacksmith can get," says Espelund.
     Iron with a low carbon content is malleable, without becoming brittle. However, various kinds of iron were produced depending on the application. Espelund believes this compares with the technique used in the Roman Empire.
     This first technology was in use in Norway for about 900 years, from around 300 BCE to 600 CE. Some 40 tonnes of iron per year were produced in Trondelag around the year 200 CE - much of it probably exported to Europe, where phosphorus-free welding steel was sought after.
     It seems that the technology for the oldest iron production in Norway originally came from the east, perhaps from Georgia. Georgian furnaces are about 500 years older than the Norwegian ones. The technology may have come to Scandinavia from the Middle East.

Edited from ScienceDaily (8 July 2015)