A possible medieval recycling technique – smelting iron using hammerscale

Abstract

Hammerscale is a common by-product of the forging process of iron and it may appear in a large amount in the ancient smithy workshops as well. Its recycling (i.e. re-smelting) in early bloomery furnaces might have been an economical and reasonable process, although it is not known whether it works or not, and also there is no archaeological evidence for this technique. In our recent investigation, flaky hammerscale was smelted using the copy of the 8-10th century embedded furnaces of the Avars and the conquering Hungarians. The resulting bloom was processed to a billet and its chemical composition was further examined. Hammerscale proved to be an excellent raw material for the early bloomery iron smelting technology: good iron yield could be achieved due to the high reaction surface and iron content. Moreover, the extracted bloomery iron had low carbon content and had a very low amount of undesirable impurities, e.g. P, As. Cu, S. etc.