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Introduction to the archaeometallurgy of iron
Donald B. Wagner

Direct iron smelting in Scandinavia in recent centuries

Bloomery smelting was practised in Denmark until about 1600, in Norway and Sweden until rather later, perhaps the early 19th century. The ore used was bog ore, a mineral that precipitates from iron-rich waters under certain specific pedological conditions. It is often found in bogs, but also in other soils. It can be in the form of clumps that resemble roots, or in larger blocks, or as a crumbly red, brown, or yellow soil (Buchwald 1998). It is usually said that bog ore was not much used in iron production outside of northern Europe, but it may have been used in China, as a passage and illustration in Song Yingxing’s Tian gong kai wu 天工开物 (1637) seems to indicate.

Sweden

There are numerous early Swedish accounts of bloomery smelting, and these have been studied by Lars-Erik Englund (2002: 52–54; 89–168). Of these, Lars Schultze’s from 1732 seems the most useful for our purposes. Here are his illustrations:

Lars Schultze’s diagrams of a Swedish bloomery furnace, 1732 (reproduced here from Björklund 1982: 522, 523, 527). A redrawing of no. 3 from 1845 is here.

A scientific study of the operation of a bloomery which was very similar to Schultze’s took place in 1851. Four smelts, performed by men who remembered how it had been done in the past, were observed by professional metallurgists from the Swedish Ironmasters’ Association. Their report was published in Swedish in 1946 and later translated into English (Busch 1972). The following depends very heavily on a discussion by V. F. Buchwald (1991: 271–273).

The furnace was filled with dry wood and ignited from below. After 30 minutes, after the wood was charred and had descended, a few shovelfuls of roasted and pulverised ore were added. Blast (in this case from a water-driven bellows) was blown in near the bottom, and this was increased as the process continued and more wood and ore were added. At a certain point charcoal began to be added instead of wood; it burned more quietly and allowed the furnace operator to see what was happening.

After 2–2½ hours the furnace burden had sunk down into the rectangular bottom of the furnace, and now the operator’s skill came to the test. He worked with a hook, a pointed rod, and a spade, manipulating the remaining furnace contents to separate the metallic iron from the slag and gather it together into a compact bloom. During this operation the blast was carefully regulated to avoid oxidising the iron.

Finally the blast was stopped and the bloom, typically weighing 8 kg, was fished out with tongs and taken quickly to an anvil, where it was cloven with an axe but not further hammered. Later it would be reheated and hammered to squeeze out the slag, producing 4–5 kg of wrought iron.

Lars Schultze’s illustration shows a young boy cleaving the bloom with an axe. The drawing is unrealistic, for this was hard work, as can be seen in this video from an American demonstration smelt. (The video comes from Guss Bort’s Facebook page.)

This particular furnace had no taphole for slag. It was cleaned out from the top, then immediately charged for the next heat. The operations continued day and night for a week or more, until the stock of ore, wood, and charcoal were used up.

This type of bloomery is unusual: it appears to be a solidly built permanent installation, rather than one that is abandoned after a few smelts. The continual operation for a week or more must give a considerable saving of fuel, since in most bloomeries a great deal of fuel is used for the initial heating of the furnace before smelting begins.

Norway

Ole Evenstad in 1790 described a a bloomery similar to Schultze’s, but smaller, used by Norwegian peasants. Here are his diagrams:

Reproduced from Evenstad 1790.

Niels L. Jensen (1968) has given a summary English translation of Evenstad’s Dano-Norwegian description.

The Norwegian Forest Museum regularly holds demonstrations of bloomery smelting according to Ole Evenstad’s description. In this short film we follow a school class attending such a demonstration. Don’t worry about the Norwegian commentary, just watch.

The schoolchildren first go out to find bog ore, and what they find is a red earth. They are asked to test it on the tongue. The ore is roasted. They pump the bellows as the ore and charcoal are charged into the furnace. They watch as the bloom of iron is removed and cloven. (The film does not show the bloom being hammered to compact it and remove slag.) Finally they see a blacksmith hammering the iron.

Denmark

In Denmark, bloomery smelting was dead by 1600, so we have very little information about Medieval and late Danish bloomeries. (We know a great deal about earlier bloomeries from archaeology.) My teacher Vagn Buchwald has considered the available material and concluded that the furnaces used resembled pit furnaces like the one excavated in Guangxi. He drew this explanation of the process:

Reproduced from Buchwald & Voss 1992.

References

Björklund, Stig, ed. 1982–1987. Lima och Transtrand: Ur två socknars historia. 2 vols. Malung: Malungs Kommune. Vol. 1: Myrjärn och smide, 1982. Vol. 2, 1987. In Swedish.

Buchwald, V. F. 1992. ‘Jernfremstilling i Danmark i middelalderen – lidt om bondeovne og kloder / Eisenverhüttung in Dänemark im Mittelalter: Etwas von Herdgrubenöfen und gespaltenen Eisenluppen (“Klode”)’. Aarbøger for nordisk oldkyndighed og historie, 1991: 265–86. In Danish with German abstract and tr. of figure captions.

Buchwald, Vagn Fabritius. 1998. ‘Myremalm’. Geologisk tidsskrift 1998.1: 1–26. In Danish.

Buchwald, V. F., and Olfert Voss. 1992. ‘Iron production in Denmark in Viking and Medieval times’. In Bloomery ironmaking during 2000 years. Vol. II: Iron in the West Nordic region during the Middle Ages, edited by A. Espelund, pp. 31–43. Trondheim: Budalseminariet.

Busch, J. A. W. 1972. ‘Iron by the bloomery process at Nornäs, Sweden, in 1851’. Journal of the Historical Metallurgy Society 6.1: 28–33. Translation from Solders 1946: III–X.

Englund, Lars-Erik. 2002. Blästbruk: Myrjärnshanteringens förändringar i ett långtidsperspektiv. (Jernkontorets Bergshistoriska Skriftserie 40). Stockholm: Jernkontoret. In Swedish.

Espelund, A., ed. 1991–2. Bloomery ironmaking during 2000 years. Seminar in Budalen, Sør-Trøndelag, Norway, August 26th – 30th 1991. “In honorem Ole Evenstad”. 2 vols. Trondheim, Norway: Budalseminaret.

Evenstad, Ole. 1790. ‘Afhandling om Jern-Malm, som findes i Myrer og Moradser i Norge, og Omgangsmaaden med at forvandle den til Jern og Staal. Et Priisskrift, som vandt det Kongelige Landhuusholdnings-Selskabs 2den Guldmedaille, i Aaret 1782’. Det Kongelige Danske Landhuusholdningsselskabs Skrifter D.3: 387–449 + Tab. I–II. In Danish. Partial English translation Jensen (1968). Annotated ed. Espelund (1992).

Jensen, Niels L. (tr.). 1968. ‘Ole Evenstad, “A treatise on iron ore as found in the bogs and swamps of Norway and the process of turning it into iron and steel”’. Bulletin of the Historical Metallurgy Group 2.2: 61–65. Abridged translation of Evenstad (1790).

Solders, Severin. 1946. Älvdalens Sockens historia. Del III: Myrjärn – hemsmide – liebruk. (Dalarnes Fornminnes och Hembygds Förbunds skrifter 9). Facs. repr. Grycksbo: Strålins, 1994. In Swedish.

Last edited by DBW 28 February 2023