Roman copper metallurgy: the Conimbriga situlae handle attachments

Abstract

The Romans are probably the best-known civilization of the Ancient times in the Western world – from architecture to monumental statuary, from the monetary system to the military strategies and the development of mining on an industrial scale, among many other fields of knowledge, have been widely studied. This vast amount of knowledge has been built largely due to archaeological evidence, but also because of the existence of contemporary written sources. In the Iberian Peninsula context, Conimbriga arises as one of the most important Roman archaeological sites when looking at the quantity, quality and diversity of their heritage. Concerning the Cu-based metallurgical productions, little is known in contrast with other imperial territories. The purpose of this study is the investigation of copper alloys from situlae and their components – handles and attachments – from Conimbriga in order to establish eventual relationships between elemental composition, thermomechanical processes and typology. Additionally, similar artefacts from Bracara Augusta and Corredores were also studied in order to verify eventual correlations with Conimbriga “productions”, and also, to identify the possibility of local productions versus the importing of artefacts by comparing the results with those obtained on similar artefacts recovered from other Roman sites with the aim of providing a better comprehension of the Roman copper-based metallurgy in the Iberian Peninsula. The archaeometallurgical study was performed using non-invasive and micro-analytical techniques, such as micro-energy dispersive X-ray fluorescence spectrometry, optical microscopy and scanning electron microscopy, in order to respect the ethical principles applied to the study of cultural heritage. The main results showed that the Cu-based metallurgy of roman situlae, attachments and handles from the Portuguese territory reveals some conservatism by the singularity of the presence of leaded coppers in some of the attachments and handles in comparison to the italic productions dominated by the presence of significant levels of Sn. In opposition, it also showed the prevalence of the usage of contemporary Roman Cu-based alloys, such as the mixture of Cu with Sn and Zn with or without Pb, besides the consistent usage of leaded bronzes as it was observed in other Roman provinces, namely in Britannia. This particular metallurgical production from Conimbriga also evidences technological versus economic factors as the main vectors for the type of alloy chosen to produce the different type of artefacts and lastly the aesthetical reasons related to the golden colour appearance promoted by the presence of the more expensive alloying elements found in the Roman Cu-based alloys: Sn and Zn. The incursion through the joining processes led to some important results in the particular field of Roman soldering, pointing to the use of Sn or Sn-rich soft solder to join the attachments to the situla.