The isotopic composition of tin, copper and lead in archaeological tin and bronze objects can be used to answer questions regarding origin of the source material, production techniques (e.g. recycling) or the relationships between artefacts and can also be helpful for questions concerning geological material (e.g. ores).
The isotope ratios of elements in rocks and cultural-historical objects varies often. One reason for these variations is the radioactive decay of so-called unstable isotopes, for example of Rb, U or Re, which affects the isotope compositions of Sr, Pb or Os. On the other hand, stable isotopes which do not decay any further, but can be radiogenic, e.g. produced by radioactive decay, are also separated from other Isotopes of the same element owing to their mass differences. This may happen in the course of physical (e.g. diffusion, evaporation), chemical (e.g. smelting, oxidation, reduction) and biological processes, which is called isotope fractionation. Such processes are great tools to study both the production of cultural-historical objects (metals, alloys, slags, ceramics, glass) and the formation of their starting materials (ores, minerals). These tools provide the reaction products with a specific isotopic fingerprint, which offers information: one on the nature of the source of the element in question and the other on the transfer process from the source to the reaction product.
However, for the determination of origin of the source materials it can be estimated that a single isotope system, as for example Sn, can only be used to a limited extent due to large variations in the isotope compositions of the ore deposits. Therefore, it is not possible to determine the exact origin of the source material, but we are able narrowing down the possible origin. This is primarily owing to the isotopic overlapping of the different tin deposits, which means that it is only possible to exclude specific deposits. Thus, if the isotope ratios are mismatching, deposits can be excluded, but a positive correlation and therefore allocation is not possible. For testing these hypotheses of provenance, the integration of additional data from other isotope systems, geochemistry (chemical composition) or even from the archaeological sciences are useful. In addition, this so-called multi-parameter approach also holds great potential with regard to the specific interrelationships of artefacts with each other. By combining Sn, Cu and Pb isotopes with the chemical composition, for example, questions regarding material mixtures or recycling can be investigated. For the determination of the origin, it is important to formulate a precise question, because a suspected link of origin between object and deposit can be answered unambiguously negative if there is no match. However, a positive assignment is not mandatory as long as all other possible areas of origin cannot be excluded. Therefore, a comparison with a database of deposits is necessary. It must be noted that the Pb content in tin ores is noticeably low and thus the lead isotope ratio is overprinted in archaeological artefacts by the higher Pb content of the copper ores, thefore the lead isotope ratio of an archaeological artefacts gives us information of the provenance of the copper ore, but not from the tin ore.
The isotopic composition can be used in different materials, on the one hand, for classification and on the other hand for determining the origin of the raw materials. In the case of a group of objects, it can be checked whether they consist of the same material or of different materials with possibly different origins. For the determination of the origin, it is important to formulate a precise question, because a suspected link of origin between object and deposit can be answered unambiguously negative if there is no match. However, a positive assignment is not feasible as long as all other possible areas of origin cannot be excluded. Therefore, a comparison with a database of deposits is necessary.