Lars-Erik Englund lars-erik.englund@swipnet.se

Before the experimental furnaces were built in 1989 the project "Early Iron Making in Kind" had been ongoing for many years. It started in 1982 when the local History Association in the parish of Tranemo, in south-west Sweden, began mapping charcoal pits and slagheaps. This work was intensified during 1984 and 1985 when the state organised survey of ancient monuments came to this region. This survey, organized and carried out by The Central Board of National Antiquities, included all kinds of ancient monuments, but particular attention was given to the bloomery sites. In all we have documented 87 bloomeries in Tranemo and about 190 in all of the jurisdictional district of Kind. This figure can be compared with approximately 7000 bloomeries, and 850 blast furnaces, in the whole of Sweden.

A new method of surveying charcoal pits and slag heaps was invented. Tools were developed to locate these very difficult, hardly visible structures in or on the ground. With a soil-probe, metal-needle, knife, gardening spade and a magnet it was possible to find many slagheaps and sometimes even roasting places, anvil stones, anvil slag and smithing pits in the woods. Questions about technic and site organisation was raised and in 1987 the first excavation started. Until autumn 1993 the local History Association in cooperation with Lars-Erik Englund carried out three excavations, two in the village of Arnås in Tranemo and one in the village of Örsås in Örsås parish, 30 kilometres west of Arnås.

In all three cases we found a pair of furnaces, a technic and organisation which seems to dominate in the region. During the period AD 800-1350 there are, as far as we know, no other technique used. Before this period there are rare examples of a different kind of furnace, with diffrent slag, e.g. no tap slag, and no spatial connection with the charcoal pits. At about AD 1350 it seems that bloomery iron making disappeared but iron smithing did not. Scythe smithing is rather famous in this bloomery region up to the beginning of the 20th century. Twin furnaces are not spread all over Sweden. They are to be found only in the south-west parts, in the counties of Västergötland, Halland and Småland. Halland belonged to Denmark before the middle of the seventeenth century. Furnaces somewhat similar to the twin furnaces, dating back to Viking Age, have been reported from Norway but not from the Danish mainland.

In parts of Europe twin furnaces have been reported from Bellaires and Boécourt in Switzerland and from the neighbourhood of Montpellier in southern France. These European twin furnaces are a few hundred years older than their Swedish counterparts. It is, however, interesting to note that the twin furnace technique was only used by the Vikings facing towards the western parts of Europe. This technique was not used by the Vikings in eastern Sweden. It seems that Viking Age iron making technology in eastern Sweden was, in many ways, traditional and had strong roots back into Roman times.

The twin furnaces are mainly built on flat ground, in a stone casing, about one metre apart. Sometimes they are built in a slope, as in Örsås. The need for stones is less in this case. The furnace shafts were generally about 80-85 cm high, round to oval, 30-40 cm wide, clay lined and they had an arch for tapping slag. Slag tapping channels in front of the furnaces as well as tap slag in the slag heaps confirm this interpretation. Fuel used was certainly charcoal. Small pieces of wood may also have been used, but this is difficult to prove archaeologically. The ore used was red earth, a powdery ochre, dried and roasted before being charged. The way of working the furnaces has given a particular shape to the slag heap, a kind of croissant-like shape, with the furnaces located centrally at the inner bend. Reduction slags are situated at both ends and roasted ore behind the furnaces. In the case of Örsås clay was stored behind the furnaces. Where anvil stones have been located there have also been anvil slags in the form of crushed slag, magnetic spherical prills and flat slag. Hammer scale has not been found, indicating that secondary smithing took place somewhere else.

The excavations gave answers to many questions but also introduced new ones. Next step was to build a set of experimental furnaces. This was realised in 1989 and since then attempts have been made to recreate iron making of the Viking Age. The learning process is very slow and it is very easy to begin to follow a wrong track. But the main point with experimental archaeology is to start asking questions one didn't think of before and to gain a complementary set of data useful when discussing the archeologial record and its interpretaion.

The earliest experiments were tentative. There was no iron produced at all until the sixth try. In all we have got small amounts of iron in four of the first 23 experiments. It was difficult to reproduce a fairly good process, even though keeping all parametres the same. There were no attempts to smith the iron before experiment 25. One of the furnaces was rebuilt during the summer of 1993. For the first time it was given a complet clay lining and the rectangular iron tuyere was changed to a nozzle which went through a clay mouthpiece and ended 4 cm inside the furnace. In experiment 24 the temperature was measured at ten points. The distribution of temperature was not as expected. It had been to low in the reduction zone, between 1100 and 1200oC. In the following experiment the air rate was increased from four blows per minute (300 l/min) to five blows per minute (375 l/min).

Experiment 25 resulted in a bloom better than anyone before. For the first time bloom smithing was carried out by a part-time smith, by using the furnace as a hearth. Five reheatings gave a more consolidated block of iron, though still full of voids and slag, weighing 1,6 kg. A knife was made of loose iron-drops in slag which were not attached to the bloom. The smith used modern steel for the edge but bloomery iron made from red earth for the blade. His comments about smithing this iron was short: this is good iron, soft, strong and easy to smith!

We had another breaktrough in XP 36, performed in August 1995. For the first time we succeded in making steel, and also for the first time, we got more tapslag (5,3 kg) then furnace slag removed through the furnace top (2,5 kg). The temperature in the slag-bath rose to 1300oC during the process. The one-time consolidated bloom, weighing 3,8 kg, was later cut into four pieces (0,45 + 0,4 + 0,4 + 1,9 kg). The 0,45 kg piece was smithed into a bar (15 x 1 x 1 cm) and it did not break during fold-welding. Hardening in cold water showed steel right through the bar. A file did not make marks on the bar surface.

Until now 37 experiments have been carried out. The last thirteen XP:s have all resulted in smithable iron. Iron losses are great. The yield from ore to implement is about 10-15%, but still there is enough iron to smith knifeblades, hooks, nails and other objects.

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