Lead Isotope Provenance

Lead isotope provenance traces metals — copper, silver, lead, and lead-bearing glazes and pigments — back to the ore deposits from which they were extracted, by measuring the ratios of lead's four naturally occurring isotopes. Three of those isotopes (lead-206, -207, -208) are produced by the slow radioactive decay of uranium and thorium, while lead-204 is primordial, so the isotope ratios of an ore depend on the age and the original uranium, thorium, and lead content of the deposit. These ratios are fixed at the geological scale and are not altered by smelting, so they survive into the finished artifact. As Renfrew and Bahn note in their survey of provenance science, comparing an artifact's lead isotope signature to the isotopic fields of candidate ore deposits can identify, or at least constrain, the source of its metal. The method sits within the broader geoarchaeological toolkit of compositional and isotopic sourcing.