Rauasulatus kui uurimisteema ja praktilise väärtusega pärandtehnoloogia: tähelepanekud aastatest 2019–2025 / Iron Smelting as a Research Topic and a Heritage Technology of Practical Value: Observations from 2019 to 2025

Abstract

The article explores the direct reduction of iron as an ancient technology where solid bloomery iron is produced from bog ore using charcoal and carbon monoxide both from the perspective of scientific research and as a practically applicable traditional technology. The article draws on my experiences of archaeometallurgical research in Estonia and on my own experiments carried out between 2019 and 2025. The article focuses on the production of iron from bog iron ore, its historical background, contemporary experiments, and the value of iron smelting as a means of self-expression in craft.

Local iron production was widespread in Estonian territories from the Roman Iron Age until the 14th century, when cheaper high-  quality osmund iron imported from Sweden entered the market. The largest historical centres of iron production in Estonia were the Tuiu region of Saaremaa and Virumaa. Despite its historical disappearance, the skill of iron smelting has been revived in recent decades by researchers, reenactors, and metal artists.

Modern interest in historical iron production in Estonia emerged in the 1960s, when archaeologists discovered several ancient iron smelting sites. The first practical experiment using local bog ore was carried out by Arvi Lauringson in 1978, but it was not until the late 1980s that the archaeologist Jüri Peets achieved successful results. His research and experiments laid the foundation for experimental archaeological iron smelting in Estonia and became an important scientific starting point for the entire field. A new wave of activity in this field began in the 2010s, when iron smelting workshops started to be organised at the Estonian Academy of Arts, the Viljandi Culture Academy and at various heritage events. Nils Hint, Karmo Kiivit, Ragnar Saage, Götz Breitenbücher and several other metal artists, researchers and blacksmithing enthusiasts have led workshops that have transformed direct reduction back into an active heritage technology. I began iron smelting in 2019 and have, ever since, organised iron smelting experiments every summer.

Finding suitable ore is essential for successful iron smelting. Historically, bog iron ore – found in fens, river floodplains and on the edges of transition bogs – was used in Estonia. The article describes how ores can be identified in the landscape and offers tips for finding suitable soil types using the Estonian Land Board’s soil maps (Figure 1), where soil codes M and S indicate appropriate bog soils. The ore is roasted in a fire to remove moisture and organic compounds and to make the iron compounds more readily reducible. The ore is then crushed into pieces the size of peas (Photo 2). Charcoal must also be prepared, as it serves both as fuel and as a way to reduce carbon monoxide in the process.

A smelting furnace made of clay, hey and firebricks is built for the direct reduction of iron (Figure 2). The first furnaces used in the experiments were approximately 70 cm high. Over the years, the dimensions of the furnaces have gradually increased up to 90 cm, approaching the medieval Tuiu furnace types found on Saaremaa. Once the furnace has dried out and the ore has been roasted, the stove must be heated. It starts with a small fire, with wood added from time to time. Once about half a furnace-full of charcoal has burnt out, one can refill it with charcoal and start adding ore. During the smelt process ore and charcoal are gradually added in a ratio of one to one. During smelting, liquid slag forms at the bottom of the furnace, which must be drained from time to time to ensure that the flow of air is not interrupted. Air is fed into the furnace using a bellows or a fan, and the temperature must be kept high enough for the reduction process to take place (Photo 6).

Successful production depends on the chemical composition of the ore. Some ores produce abundant slag, while others require mixing to trigger the correct reaction. Ores from different locations in Estonia behave significantly differently in the fire. Once 40–50 kg of ore has been processed, the furnace is dismantled (Photo 7) and the bloom – a mixture of iron and slag – is extracted. The forging of the bloom iron then begins, during which the slag is removed and the structure of the material is compacted. Through repeated heating and forging, usable raw iron is produced, from which tools or weapons can be made. I use the iron produced mainly to craft laminated knives (Photos 11, 12).

The direct reduction of iron (iron smelting) is not merely a historical technology, but a living heritage that connects science, craftsmanship, and creativity. Modern experiments confirm that it is still possible today to produce high-quality, forgeable iron from local bog ore. The value of iron smelting lies not only in the preservation of technical knowledge, but also in community engagement, creativity and the opportunity to reconnect with the skills of ancestors. I hope that an increasing number of enthusiasts will discover the world of historical iron production for themselves.

Keywords: iron smelting, direct reduction of iron, experimental archaeology, ancient metallurgy, bog iron ore, bloom iron