|
Beta Analytic
|
Isobar Science
|
This post is sponsored by Beta Analytic.
Isotopic Analyses of Metal Artifacts and Glass
The analysis of strontium (87Sr, 86Sr) and lead (204Pb, 206Pb, 207Pb, and 208Pb) isotopes within metal and glass artifacts can provide important insights into artifact origins. Lead and strontium are naturally occurring elements found within the earth’s crust as well as in bodies of water, soil, and overlaying plants. Because of this, their isotopic signature acts as a conservative tracer and can be pinpointed to the geologic origin of their host rock, particularly as certain processes (e.g. weathering) do not impact isotopic compositions. These are known as provenance studies and have proven adept at tying artifacts to the rock/ore material used in its creation unaffected by metallurgical process. These studies can be direct, if the artifact is made from rocks/ore deposits (e.g., metals), or indirect via overlaying soil, water, plants, or even animals consuming local plants and water. When the local origin of a metal artifact is known, further analysis into trade relationships and the movement of objects through time can be explored.
Pb is particularly useful in estimating the geological origin of the metal within artifacts. The mining of lead and its presence in the archaeological record goes back millennia. Some of the earliest examples dating back to the 5th millennium BCE (Yahalom-Mack et al. 2015), with extensive use beginning in Ancient Egypt (Science, 2010). This was followed by the development of lead mining by the Romans – later expanding into Europe and Britain (Durali-Mueller et al. 2015; Montgomery et al. 2010). As lead does not significantly fractionate during the melting process it is possible to decipher this origin in objects where lead is a major element (e.g., lead pigments, lead bronze) as well as in objects where lead is a minor element (e.g., copper, brass, iron, silver). Lead isotopes undergo a variety of processes from source mining to smelting, to refining and casting – ultimately leading to the development of artifacts where lead is a major (lead pigments and metals) or minor (glass, copper, iron, glaze, silver) element. While evidence varies, it’s been generally accepted that lead isotopes remain unchanged despite these processes (Macfarlane, 1999; Stos-Gale and Gale, 1999). Metals that are made up of more pure elements (e.g., native copper) tend to be more challenging when analyzing source as the isotopic signature tends to overlap with many different potential source regions (Rapp et al. 2000). On the other hand, where metal artifacts are developed from impure sources with unique chemical properties (e.g. pewter), provenancing can be completed with more certainty (Copper and Simonetti, 2021). Recent advances in analytical capabilities have permitted more accurate archaeometallurgy investigation through the improvement of mass spectroscopy analysis certainty – currently approximately ±0.1% – sufficient to allow for the differentiation of lead isotopes from a variety of sources.
Under the same theory, ancient artifacts that include glass elements can be provenanced based on lead isotopes, as well as strontium isotopes. Glass is constructed using a series of different elements – each having distinct origins. The glass “former” is usually developed from silica sources (i.e., quartz), which is abundant in the Earth’s crust and is a common constituent of sand. Quartz has a distinct lead isotopic signature. The glass “stabilizer” is often produced from lime, which has ties to local soil and geology with specific strontium and oxygen isotopic signatures. Early examples of glass include glazed windows and stained glass – with early examples in ancient Rome (Fleming, 1999) and St. Paul’s Monastery in England (681 AD, Historic England 2024), respectively.
Contact Isobar Science to learn more about how isotopic analyses can help you provenance metal and glass artifacts.
Isobar Science, a subsidiary of Beta Analytic, specializes in isotope services for Geochronology, Geochemical Fingerprinting, and Environmental Source-Tracking, providing high-precision research-quality and timely data. Isobar Science performs measurements using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS).
References
Cooper, H.K. and Simonetti, A., 2021. Lead Isotope Analysis of Geological Native Copper: Implications for Archaeological Provenance Research in the North American Arctic and Subarctic. Minerals, 11(7), p.667.
Durali-Mueller, S., Brey, G.P., Wigg-Wolf, D. and Lahaye, Y., 2007. Roman lead mining in Germany: its origin and development through time deduced from lead isotope provenance studies. Journal of Archaeological Science, 34(10), pp.1555-1567.
Fleming, S. J. (1999). Roman Glass; reflections on cultural change. Philadelphia: University of Pennsylvania Museum of Archaeology and Anthropology.
Historic England, 2024. https://www.english-heritage.org.uk/visit/places/st-pauls-monastery-jarrow/history/
Macfarlane, A., 1999. The lead isotope method for tracing the sources of metal in archaeological artefacts: strengths, weaknesses and applications in the western hemisphere. BAR International Series, 792, pp.310-316.
Montgomery, J., Evans, J.A., Chenery, S.R., Pashley, V. and Killgrove, K., 2010. ‘Gleaming, white and deadly’: using lead to track human exposure and geographic origins in the Roman period in Britain. Journal of Roman archaeology; supplementary series., pp.199-226.
Rapp, G.R., Allert, J., Vitali, V., Henrickson, E. and Jing, Z., 2000. Determining geologic sources of artifact copper: Source characterization using trace element patterns. University Press of Amer.
Science, 2010. Egyptian Eyeliner May Have Warded Off Disease. Archaeology News. doi: 10.1126/article.30976
Stos-Gale, Z.A. and Gale, N.H., 2009. Metal provenancing using isotopes and the Oxford archaeological lead isotope database (OXALID). Archaeological and Anthropological Sciences, 1(3), pp.195-213.
Yahalom-Mack, N., Langgut, D., Dvir, O., Tirosh, O., Eliyahu-Behar, A., Erel, Y., Langford, B., Frumkin, A., Ullman, M. and Davidovich, U., 2015. The earliest lead object in the Levant. PLoS One, 10(12), p.e0142948.