Iron Metallographic Analysis

Investigation of artefacts can vary from visual examination, through low-power binocular microscopy and radiography to metallography and full-blown chemical analysis.

Combined visual examination and x-radiography should be used to identify iron artefacts, which often only appear as lumps (Fell et al. 2006). Various typologies have been created for key artefact groups. Examination of the x-radiographs may also reveal some information about methods of manufacture, presence or absence of surface features and/or non-ferrous inlays (Blakelock & McDonnell 2007).

Iron and steel artefacts are best understood through study of their microstructures (Bayley et al. 2001). Metallography shows what types of iron or steel were used, whether it has a composite structure and what treatments it underwent during and after manufacture (Blakelock & McDonnell 2007). An understanding of how metals’ physical properties were manipulated can reveal much about how metals were used and valued in a society.

In an ideal world a proportion of metal artefacts from all excavations should be routinely analysed alongside any production refuse. If this sort of approach is to be adopted, it would be desirable for all developer-funded projects to have funding for analysis of metal-related finds routinely written in (Bayley et al. 2008). The arguments against such a policy are the risk of damage caused by sampling for a quantitative analysis, but the benefits of this analysis outweighs this factor (Blakelock fourthcoming). Analyses of metal artefacts need to be conducted on a sufficiently large scale to be representative; one or two analyses are generally not sufficient to characterize manufacturing practices, an artefact type or culture group (Bayley et al. 2008).

• Analysis can reveal how the object was constructed. Analysis of radiographs can inform on macro-fabrication, e.g weld lines and shape (Fell et al. 2006). Metallography, on the other hand, can reveal far more about how the object was made, what alloys were chosen and what heat-treatments were applied. This can be very informative about an artefact’s intended use and its place in the culture that produced it (Blakelock & McDonnell 2007).
• Metallograpy can reveal the technological choices made when producing artefacts (Blakelock forthcoming). It can reveal culturally specific strategies and how these relate to ideas of ethnicity and belonging.
• A combination of metallography and chemical analysis of the iron can reveal some details about the smelting technology. The presence or absence of phosphoric iron is a possible indicator of bog ores being used (McDonnell 1989). In addition, chemical analysis of slag inclusions can indicate ore type, the efficiency and nature of the smelting process, furnace parameters, whether fluxes were used.

Full x-radiography of all artefacts (even nails) is highly recommended as the identification of some artefacts can be hampered by corrosion products. This should be carried out prior to the assemblage being sent to me, or can be carried out by myself for an extra cost. The cost of examination and identification of iron artefacts is determined by the size of the assemblage. The approximate charge is £300 per day.

For metallography of specific artefacts, the equipment is relatively inexpensive but metallography is very labour-intensive, which does increase cost. Therefore the price per artefact for metallography alone is £200 per artefact. But to be certain of the alloys used SEM-EDS analysis is required therefore for metallography and SEM-EDS analysis it is £350 per artefact. Analysis of individual artefacts is rarely beneficial therefore discounts can be provided for large sample sets. There may be discounts for charity/amateur groups or assemblages that fit within my research interest.

Bayley, J., Crossley, D. and Ponting, M. 2008. Metals and metalworking. A research framework for archaeometallurgy. London: Historical Metallurgy Society

Bayley, J., Dungworth, D. and Paynter, S. 2001. Centre for Archaeology guidelines: archaeometallurgy. London: English Heritage.

Blakelock, E. 2012. Cutting Edge of Technology: How the archaeometallurgical analysis of iron knives provides an understanding of the nature of iron technology in past societies. Archaeological Review from Cambridge 26(2): 66-84.

Blakelock, E. and McDonnell, G. 2007. A review of the metallographic analysis of Early Medieval knives. Historical Metallurgy 41(1): 40-56.

Fell, V., Mould, Q. and White, R. 2006. Guidelines on the X-radiography of archaeological metalwork. Swindon: English Heritage.

McDonnell, G. 1989. Iron and its alloys in the fifth to eleventh centuries AD in England. World Archaeology 20(3): 373-382.