Silver in Early Medieval Scotland: technologies and microscopic study

Session

Poster Session Three

Authors

Dr Lore Troalen (1), Dr Janet Lang (2), Dr Jim Tate (1)

Affiliations

1. National Museums Scotland
2. The British Museum

Keywords

 Silver, hacksilver hoards, early medieval Scotland, recycling, analysis, metallography 

Abstract text

While there have been extensive investigations of Roman silver [1-3], much less work has been undertaken on post-Roman silver use. This work considers how the dwindling resources of silver were managed, utilised and supplemented in early Medieval Scotland, focussing on the period c. AD 500-600, based on the investigation of two Pictish hoards of hacksilver from eastern Scotland (Norrie’s Law, Gaulcross) [4]. 

The compositions of the silver items were investigated by Particle-Induced X-ray Emission (PIXE) with a proton beam of 3 MeV and an analytical spot of 50 µm, typically scanning a 300 µm × 300 µm area, at the AGLAE accelerator of the C2RMF laboratory. PIXE analysis was undertaken on polished micro-samples and supplemented by Scanning Electron Microscopy (FEG-SEM-EDX) and metallographic analysis to obtain information on the manufacturing techniques. 

Elemental analysis shows that the Norrie’s Law and Gaulcross silver contain significant levels of copper. While most Pictish silver samples contain 4–10 wt% copper, several of the items analysed display levels of copper between 20–37 wt%. Lead, tin and zinc are also present, ranging from 0.5 to almost 5 wt%. The proportions of the debasing alloys observed in the samples suggest the addition of leaded bronze and / or gunmetal alloys, to conserve limited supplies of silver. 

Metallographic analysis and SEM-EDX mapping revealed that the Pictish samples had been heavily worked and although they showed a few annealed, twinned grains, this treatment was not sufficient to transform the structure. None of the samples had been fully homogenised, resulting in a heavily worked and banded structure apart from one sample which was from a cast object. 

References

[1] Bennett, A., 1994. Chapter 2. ‘Technical examination and conservation’, in: Mango, M. and Bennett, A. The Seuso Treasure, Part I. Ann Arbor: Journal of Roman Archaeology, pp. 21–35.

[2] Doračić, D., Lang, J., Fletcher, P., 2017. Late Roman silver hoard from Vinkovci, Croatia – A preliminary technological overview. Historical Metallurgy 49, 87–95.

[3] Troalen, L., Lang, J., 2022. The technology of the Traprain Treasure, in The Late-Roman Silver Treasure from Traprain Law (eds. F. Hunter, A. Kaufmann-Heinimann and K. Painter). National Museums Scotland, 315–328. 

[4] Blackwell A. and Goldberg M., 2017. Norrie’s Law, Gaulcross and beyond: widening the context of hacksilver hoarding in Scotland, in Scotland in early Medieval Europe (ed. A. Blackwell). Sidestone Press, 67–84.