The evidence and the secrets of ancient bloomery ironworking in Norway

It explains some of the secrets and provides a good overview of the available research. The book also makes a short foray into the history and technology of recent industrial iron production in Norway. However, the main readership will include archaeologists, bloomery experimentalists and people interested in historical metallurgy.

The chapters (with the exception of the last) are thematically linked by the idea that bloomery archaeology makes little sense if it is not illuminated by the insights that metallurgists can provide. This theme is not laboured, but the author has made the point very strongly elsewhere:

‘These problems are beyond the scope of this humanistic discipline… It also appears that many archaeologists do not regard them as being important.’ (in Norbach, L C (Ed)(1999) Prehistoric and Mediaeval direct iron smelting etc).

He chooses example after example to show that excavation alone is not enough, and, by and large, makes the underpinning metallurgy clear and accessible. More generally there is a thoroughgoing commitment to scientific method in bloomery studies and an insistence on reproducibility as the hallmark of valid bloomery experimentation. The flip-side of this belief in modern science is a tremendous admiration for ancient technologists. This admiration is shared my most experimenters who have tried, and usually failed, to match the success of early iron makers. The author has a wide knowledge of Norse literary sources and uses this to provide insights into mediaeval iron production. But there is no hint of cultural relativism in his analysis.

The book provides a typology of Norwegian bloomeries, separating four main types corresponding to the early iron age (types 1a and 1b), Viking and mediaeval. A key example of using laboratory analysis to interpret the archaeology comes in this context: the author shows, quite convincingly, that the hellegryte type furnace was not a stand-alone production process but a preparation stage. He does this by comparing the ratio in ores and slags of the phases (FeO+MnO to SiO2) – a value he calls ‘R’. For a fully processed fayalitic slag this is just over 2. Since Fe (and Mn) flux the process, R provides an indicator of extraction efficiency, with a value of about 2 indicating the best results. The residues found with a hellegryte type had a value of about R = 12, indicating that iron had not been recovered.

A cursory glance at published values for bloomery tap slags suggests that R might be a generally useful number. It might be used to cross-check mass balance calculations (and so help in estimating ancient iron production volumes from extant slag heaps) and perhaps in addressing provenance issues.

There is at least one aspect of this book where the ‘secrets’ in its title are not revealed. Espelund asserts, citing archaeological evidence, that the early iron-age furnaces could have used dry pine wood and induced draught. He cites examples where pine wood was selected in preference to birch, correctly arguing that the resin in the pine wood increases its calorific value. He introduces the concept of a flame induced draught. This makes intuitive good sense since the exhaust gas would be loaded with CO and organic volatiles the energy of which would be released on combusting in air. However, he provides no mathematical model for this effect and no experimental data. It remains an interesting but unsupported conjecture.

The book is well made and nicely presented. The text suffers from the fact the author combines his roles of author, translator, publisher and editor. As a result there are many small typos/spelling mistakes and the English is quirky. However, with one single exception (pp 234-5) the meaning of every sentence is crystal clear. A number of the figures retain the Norwegian language labelling of their originals, which is unhelpful, but there are 171 informative illustrations and photographs and 48 tables mainly of chemical and physical properties. There is an Index of subjects and place names.

Review by J Prus (Wealden Iron Research Group)

‘The evidence and the secrets of ancient bloomery ironworking in Norway – with an extension to the beginning of the industrial period’ by Arne Espelund Arketype Pub by Arketype forlag Trondheim (2013) ISBN 978-82-996953-3-6 Hardback 319 pages 171 illustrations Price £35-00
Books can be ordered via www.arketype.no