Lead Isotopes in Archaeology

Silver items, however, are also relatively rare in the archaeological record. The most common metal found is either copper, usually alloyed with either tin (bronze) or, in the later periods, zinc (brass), or iron. The latter contains very little lead and, because of severe corrosion problems, its survival rate is often low (but see Degryse et al., 2007). Fortunately, copper can also be characterized from its lead isotope signature, since the primary ore of copper is chalcopyrite (CuFeS2), which often co-occurs with galena (PbS) and sphalerite (ZnS). Even if the ore used is a secondary mineral formed by the oxidation of the primary deposit, the copper smelted from such a deposit would normally be expected to 

The second of these assumptions has been the subject of some debate (Budd et al., 1995a), and is discussed further below. Despite these possible complications, the method of lead isotope provenancing was applied enthusiastically to copper alloy artefacts, especially those from the Late Bronze Age of the Aegean (e.g., Gale and Stos-Gale, 1992, and references therein) up until the late 1990s, when this activity virtually ceased, in part because of the contradictory interpretations which were being proposed. 

Although the technique of lead isotope analysis for archaeological provenancing has been in use for more than 40 years, it is only in the past 15 years or so that some of the fundamental assumptions have been seriously reconsidered. The major areas that have been questioned can be classified under three headings  

Although this is theoretically convincing, the key question to be answered is whether any of the ancient processes for the production of lead and silver might be expected to give such a large non-equilibrium loss. The most likely contender for a process with such losses seems to be cupellation, in which a melt of around 99% Pb with less than 1% silver is converted via preferential oxidation into an alloy with greater than 95% silver - a total loss in excess of 99% of lead (Budd 

It is clearly important to have a good knowledge of the ore geology of the area before isotopic provenancing is undertaken. Unfortunately, ancient mining is often in regions no longer considered economically viable, and the 

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Dayton, J. A. and A. Dayton (1986), Uses and limitations of lead isotopes in archaeology, Proc. 24th Int. Archaeometry Symp., pp. 13-41. 

Pollard, A. M. (in press a). What a long strange trip it s been lead isotopes in archaeology. In From Mine to Microscope - analysing ancient technology, eds. Shortland, A., Freestone, I., and Rehren, T. 

Barnes, I. L., Shields, W. R. S., Murphy, T. J., and Brill, R. H. (1974). Isotopic analysis of Laurion lead ores. In Archaeological Chemistry, ed. Beck, C. W., Advances in Chemistry Series 138, Washington, DC, American Chemical Society, pp. 1-10. 

Farquar, R. M. and V. Vitali (1989), Lead isotope measurements and their application to Roman artifacts from Carthage, Museum Applied Science Center for Archaeology Papers in Science and Archaeology, Vol. 6, pp. 39-45. 

Gale, N. and Z. Stos-Gale (2000), Lead isotope analysis applied to provenance studies, in Ciliberto, E. and G. Spoto (eds.), Modern Analytical Methods in Art and Archaeology, Chemical Analysis Series, Vol. 155, Wiley, New York, pp. 503-584. 

Stos-Gale, Z. A. (1989), Lead isotope studies, in Henderson, J. (ed.), Scientific Analysis in Archaeology, Oxford Univ. Committee for Archaeology, Monograph 19, Oxford, UK, pp. 274-301. 

Figure 9.9 Bivariate lead isotope ratio diagram for copper ores from some Aegean and Anatolian deposits, as defined by the Oxford group (Gale and Stos-Gale, 1992 Figure 13). (Reproduced with permission from Proceedings of the British Academy, vol. 77, New Developments in Archaeological Science. The British Academy 1992.)...

Barnes, I.L., Gramlich, J.W., Diaz, M.G. and Brill, R.H. (1978). The possible change of lead isotope ratios in the manufacture of pigments a fractionation experiment. In Archaeological Chemistry II, ed. Carter, G.F., American Chemical Society Advances in Chemistry Series 171, Washington D.C., pp. 273-277. 

Gale, N.H. and Stos-Gale, Z.A. (1992). Lead isotope studies in the Aegean (The British Academy Project). In New Developments in Archaeological Science, ed. Pollard, A.M., Proceedings of the British Academy 77, Oxford University Press, Oxford, pp. 63-108. 

Scaife, B., Budd, P., McDonnell, J.G. and Pollard, A.M. (1999). Lead isotope analysis, oxhide ingots and the presentation of scientific data in archaeology. In Metals in Antiquity, ed. Young, S.M.M., Pollard, A.M., Budd, P. and Ixer, R.A., BAR International Series 792, Archaeopress, Oxford, pp. 122-133. 

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