How was zinc processed into brass in the early Middle Ages?

The Greek word kαδμεία (kadmeia), the equivalent Latin cadmea and their many synonyms such as tutty, cadmia fornacum or Ofengalmei, to mention a few, are technical terms used in textual sources from Classical and Medieval times until the early Modern period to indicate different types of natural and artificial zinc-rich compounds. They were used for the production of the early orichalcum alloy, in its many definitions, and brass, a copper-zinc alloy in use from the Roman time on. This product category had its particular place in the plethora of metallurgical constituents, and for a long time was considered as a sort of tincture, a colouring agent that could give to copper the beautiful hue of gold, rather than a compound containing an alloying metal, the zinc. The problem in recognising cadmea as a source of zinc lies in the very nature of this volatile metal that evaporates at around 900 °C, a temperature considerably lower than the operational ranges of smelting furnaces. Despite its vague attribution, brass was a widespread metallurgical product whose use spans over a large period and whose history is rooted in the textual sources within important mining districts such as the Cypriot Troodos Mountains, that has been the scene of early large-scale mining and metallurgical activities, and the German Harz mountain range, which was a very important mining district for Medieval copper production in Europe. 

In late August 2024, a series of smelting experiments with polymetallic ores coming from the Harz, aimed at the study of the formation and extraction of artificial cadmea, will be conducted in the Viking Museum Haithabu, using ancient apparatuses and processes as described in the sources. These trials are aimed at understanding metallurgical uses not yet covered in research, with a broader goal to better identify zinc sources used for brass production, and with an eye also on the enigmatic appearing of this alloy in early Scandinavian and Viking contexts.

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