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Copper isotope analysis


The isotope ratios of chemical elements in natural rocks and cultural-historical artefacts can vary. One reason for this is the radioactive decay of unstable isotopes, for example rubidium, uranium or rhenium, which leads to variable isotope compositions of strontium, lead or osmium. On the other hand, stable isotopes are also separated from each other due to their mass differences in the course of physical (diffusion, vaporisation), chemical (smelting, oxidation, reduction) and biological processes. Such processes are of great importance both in the production of cultural-historical objects (metals, alloys, slags, ceramics, glass) and during the formation of their source materials (ores, minerals).

They give the reaction products a specific isotopic fingerprint. This may contain two pieces of information: firstly about the nature of the element source and secondly about the transfer process from the source to the reaction product. The isotopic fingerprint in the respective materials can then be used to answer questions regarding origin, production technique or authenticity.

The measurement of stable isotope ratios to answer archaeological questions is in its infancy, and details of isotope systematics have yet to be explored. A single isotope system often does not provide a clear fingerprint for the determination of origin, as deposits themselves can have large variations in isotopic compositions. Hypotheses can be tested by integrating additional data from other isotope systems, other geochemical methods or from the historical sciences. CEZA has state-of-the-art analytical equipment, extensive databases and natural scientists at its disposal to advise on and interpret the analytical data.


Copper has only two isotopes and the materials studied are characterised by the isotope ratio 65Cu/63Cu. The behaviour of this element is controlled by its siderophile and chalcophile properties in both geological and archaeometric contexts. In archaeology, the use of copper has been known since the Neolithic period, when it was initially used in its pure form, i.e. as a naturally occurring metal (natural copper). Since the Chalcolithic period, copper ores have also been smelted and used to produce copper alloys such as arsenic or tin bronzes. With the help of the isotopic fingerprint in the respective materials, questions regarding origin or production technique can then be answered.

The element can take on several oxidation states, with the result that its mineralogy and isotopic composition is very complex and depends heavily on the processes and environmental conditions. Copper deposits form over a wide temperature range from magmatic, hydrothermal to sedimentary and under reducing to oxidising conditions. This complexity is reflected in the great variability of the isotopic composition of copper deposits. Individual deposits can therefore not always be significantly differentiated and the copper isotope ratio can often not be used as the sole criterion for determining the origin.

However, there are clearly measurable differences in the copper isotope composition of various archaeological objects. These indicate the use of different raw material sources. The isotopic fingerprints can then be used to confirm or rule out the affiliation of individual objects or object groups, which in turn would help to interpret cultural relationships. Furthermore, in combination with elemental analysis, it is possible to distinguish between intentional and accidental alloys or to recognise mixtures of different types of metal.

CEZA offers to determine the isotope ratios of copper in minerals, copper ores and smelting products such as copper metal, bronzes and slags.

Sample composition

The sample size depends on the element concentrations in the sample, which can be very variable! For metal samples (bronze, silver, gold, tin) or cassiterite, we recommend a sample size of 50 mg. From a purely technical point of view, 1 mg or less may be sufficient. However, this small quantity raises the question of the extent to which it is representative of the total sample and whether the analysis results can be interpreted meaningfully. Representative sample quantities of copper, tin and silver ores should be at least 0.5 g, as such materials are very heterogeneous by nature.