Beyond tools and weapons: A study of iron supply and nail manufacture in Roman Aldborough, Britain

• Insights into Roman manufacturing of common iron objects. • Provenance of iron using slag inclusion analysis and multivariate statistics. • Diverse origins of metal suggest complex trade networks in Roman Britain. • Investigation of possible evidence of smithing using coal instead of charcoal. Our understanding of Romano-British iron metallurgy is mainly based on smelting remains and the analysis of bladed tools and weapons. Complementing previous research, this study examines iron nails from the Roman town of Aldborough, Yorkshire ( Isurium Brigantum), where a blacksmith’s workshop featuring extensive remains of coal, a fuel not commonly documented in Roman metallurgy, was excavated. The research investigates the manufacturing technology of the nails, contextualized within broader Roman ironworking, along with potential sources of metal and possible alterations attributable to the use of coal as smithing fuel. The manufacturing technology is explored via metallography while scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) is employed for elemental analysis of the slag inclusions. The study reveals that the nails from Aldborough are examples of typical Roman nail production with no advanced techniques such as quenching or piling being used. Carbon content shows no discernible pattern across the dataset, varying from zero to 0.8% C in spots, suggesting a lack of deliberate metal selection. Attempts to determine the origin of the metal through multivariate statistical methods (HCA, PCA, and LDA) applied to slag inclusion compositions suggest a very diverse origin of the metal spanning various regions of Roman Britain. While there is no conclusive evidence indicating the utilization of coal in the smithing process, we suggest the elevated sulfur content in slag inclusions may provide an indirect indicator, which should be further investigated in future work.