One of the main question asked of archaeologists is where an object has come from. In copper metallurgy the use of lead isotopes can reveal information about ore source and therefore the origin of an object.

This has proven more difficult for iron artefacts, which have no lead. For many years there have been very few attempts to trace iron artefacts to their source. But in the last few years researchers are moving closer to a method to provenance iron, utilising slag inclusions. My MSc and subsequent research has shown that it may indeed be possible to use the slag that is trapped in the iron during the bloomery process to provenance iron artefacts to their iron production site.Bulk element studies of slag inclusions using SEM-EDS, can be compared to slag analysed from around the country to identify possible production regions. Trace elemental studies of iron and slag may provide even more elements to identify the production site. This type of analysis works best if a possible

Bulk element studies of slag inclusions using SEM-EDS, can be compared to slag analysed from around the country to identify possible production regions. Trace elemental studies of iron and slag may provide even more elements to identify the production site. This type of analysis works best if a possible smelting site has been identified (and a selection of slag analysed for comparison). Even so there are still many questions and debates on slag inclusion analysis and provenance, some of which I discuss in my research.

Research Questions and Answers

  • Chemical analysis of the inclusions and subsequent comparison to regional data sets will indicate likely production sites.
  • Analysis of the inclusions in complex artefacts will indicate the number of different iron sources for a particular artefact.
  • Comprehensive analysis of slag and the slag inclusions within artefacts from the same site can identify whether the artefacts were made in settlement, and whether it was entirely self-sufficient.
  • Slag inclusion studies can ultimately provide data on the iron industry, the trade of iron and iron artefacts.

Costs

Slag inclusion studies tend to be quite large and require the analysis of at least 5 iron artefacts. This analysis is best carried out on bars, strips or billets, or basic artefact types e.g. nails, as these will be less influenced by the smiting process. If slag is also present on the site a comprehensive study of both the slag and the iron artefacts should be combined for the best results.

The metallography of specific artefacts, carried out prior to slag inclusion analysis, is very labour-intensive, which does increase the cost. For the analysis of the slag inclusions an SEM-EDS analysis is required, which again can be expensive, and multiple inclusions must be analysed. Given this it is best for those interested in slag inclusion analysis to get in touch so that we can discuss the various options, and costs involved. There may be opportunities to apply for external funding for specific projects. As always there may be discounts for charity/amateur groups or assemblages that fit within my research interest.

References

Blakelock, ES, Martinón-Torres, M, Veldhuijzen, HA and Young, T (2009) Slag inclusions in iron objects and the quest for provenance: an experiment and a case study. Journal of Archaeological Science 36: 1745–1757.

Dillmann, P and L’Heritier, M (2007) Slag inclusion analyses for studying ferrous alloys employed in French medieval buildings: supply of materials and diffusion of smelting processes. Journal of Archaeological Science 34(11): 1810-1823.

Hedges, REM and Salter, CJ (1979) Source determination of iron currency bars through analysis of the slag inclusions. Archaeometry 21(2): 161-175.

Paynter, S (2006) Regional Variations in Bloomery Smelting Slag of the Iron Age and Romano-British Periods. Archaeometry 48(2): 271-292.