Stephen Merkel

Carolingian and Ottonian Brass Production in Westphalia Evidence from the Crucibles and Slag of Dortmund and Soest

Introduction

Carolingian and ottonian brass production in westphalia evidence from the crucibles and slag of dortmund and soest. Explore Carolingian and Ottonian brass production in Westphalia. New finds from Dortmund and Soest reveal leaded brass made from calamine ore via microscopy.

Abstract

The abundant new crucible and slag finds from the Thier-Brauerei excavation in the center of medieval Dortmund have provided a  stimulus to revive the discussion of Westphalian brass cementation technology in the Carolingian and Ottonian periods and to explore unanswered questions concerning the process and its potential outcome. A total of sixteen crucibles and slag samples from stratified  deposits in the Dortmund-Thier-Brauerei and Soest-Plettenberg excavations were prepared for optical and scanning electron microscopy to analyze metallic inclusions, slag phases and crucible ceramic. The copper and brass inclusions within the crucibles and  their adhering slag from Dortmund show a relationship between lead and zinc contents and indicate that lead-bearing calamine ore  was heated with charcoal and copper metal to produce leaded brass. Ternary Cu-Zn-Pb alloys are common for contemporary bar-shaped ingots, which supplied casting industries in early medieval Northern European towns like Hedeby and Kaupang. Concerning the zinc-rich black slag lining the interior of some crucible fragments, they regularly showed increases in lime and iron oxides in relation to  the crucible ceramic and thus reflect impurities coming from the zinc ore. The lead-silicate slags often found in association with  crucible finds in Dortmund have yet to have a clear interpretation; although the lead isotope analysis of crucibles and lead-silicate slag  shows they may have the same source of lead, the production of the lead-silicate slag is definitely unrelated to the metallurgical process occurring inside the cementation crucibles themselves.

Review

This paper presents a compelling and detailed investigation into Carolingian and Ottonian brass production in Westphalia, drawing on a wealth of new archaeological evidence from the Thier-Brauerei excavation in Dortmund and additional finds from Soest. The authors aim to revive and deepen the discussion around early medieval brass cementation technology, addressing long-standing questions about its processes and outcomes. Through a rigorous analytical approach utilizing optical and scanning electron microscopy on sixteen crucible and slag samples, the study successfully elucidates key aspects of brass production, offering a significant contribution to the understanding of early medieval metallurgy and industrial practices. The core strength of this work lies in its meticulous material analysis and the precise deductions drawn from it. The findings clearly indicate that a lead-bearing calamine ore was heated with charcoal and copper to produce leaded brass, a composition that aligns with contemporary bar-shaped ingots found in major Northern European trading centers like Hedeby and Kaupang. The detailed examination of zinc-rich black slag lining the crucibles further illuminates the process, revealing impurities like lime and iron oxides originating from the zinc ore. While the precise interpretation of associated lead-silicate slags remains an open question, the authors' honest presentation of this ambiguity, coupled with initial lead isotope analysis, demonstrates a thorough and critical engagement with their data. Overall, this abstract promises a highly valuable and well-executed study. The interdisciplinary approach, combining archaeological excavation with advanced material science, provides a robust foundation for its conclusions. The specific identification of a lead-bearing calamine process, and its connection to broader early medieval trade networks through ingot analysis, significantly enhances our understanding of technological sophistication in the period. While the unresolved nature of the lead-silicate slags presents a minor interpretive gap, it also highlights an intriguing avenue for future research. This work appears to be an exemplary piece of scholarship that will be highly relevant to archaeologists, metallurgists, and historians of technology.

Full Text

Comments

You need to be logged in to post a comment.