Portable XRF on Prehistoric Bronze Artefacts: Limitations and Use for the Detection of Bronze Age Metal Workshops

Bronze Age metal workshops are identifiable through mistakes and traces of the crafting process on metal artefacts (Nørgaard 2018). During a study on bronze artefacts of the Nordic Bronze Age, the question arose if these workshops are also unique in their metal –the trace elemental composition of the artefacts –as the theoretical assumption of a technical fingerprint suggests. A case study tested scientific devices that can be used to collect data for such a study – EDXRF, SEM and pXRF. The investigated material are bronze artefacts of defined workshops between 1500-1100 BC in Denmark and northern Germany. In this presentation, the results of three analytical methods are compared, and the limitations of every method are demonstrated. In order to investigate the use of portable XRF technologies for the detection of crafting-related differences in the alloys, an experiment was conducted on corroded bronze artefacts. Two different scientific analyses—one destructive (sampling and SEM) and one non-destructive (pXRF)—were carried out on two artefact assemblages each related to a specific technological tradition (workshops). Results documented on the thin-sections of the first artefact group highlight a distinct change measured within the elemental composition from the bulk metal to the surface in the corrosion crust of the copper-tin alloy. These documented changes greatly influenced the interpretation of the data obtained by the pXRF. A third artefact assemblage consisting of artefacts of a distinct workshop on Zealand was analysed via EDXRF by using drilled samples. The results obtained here clearly show the assumed similarities in metal use. This study defines the possibilities and limits of non-destructive analytical techniques using a specific example. The elemental changes that can occur on the surface of corroded bronze ornaments change the element composition in such a manner that the original alloy cannot be traced via a non-destructive pXRF method.