FrankN
Regular Member
I have decided to make this new thread to present and discuss a number of recent, primarily archeometalurgical studies that shed more light on long distance bronze-age trade connections across Europe. This thread is meant to complement, not to replace, related threads, especially on the diffusion of metallurgy (which deals with a different, earlier time horizon), and the bell-beakers (which deals with a singular, albeit important aspect of these networks).
Before presenting individual findings, it makes sense to look a bit at archeometalurgical methodology and its limitations. Essentially, the approach is to look for impurities in bronzes, and compare these impurities to various known or supposed sources of bronze-age copper. A specific focus is placed on analysing various lead isotopes, the mix of which is typical for certain ore sources. This approach has several caveats:
In summary, this is still very much work in progress, and it is advisable to treat findings with some care.
Before presenting individual findings, it makes sense to look a bit at archeometalurgical methodology and its limitations. Essentially, the approach is to look for impurities in bronzes, and compare these impurities to various known or supposed sources of bronze-age copper. A specific focus is placed on analysing various lead isotopes, the mix of which is typical for certain ore sources. This approach has several caveats:
- Results depend on the selection of ore sources considered. Some sources appear to have similar signatures (e.g. Crete and Mansfeld/ Harz https://archive-ouverte.unige.ch/unige:15011, or the Massif Central and Sardinia). As such, all links established so far should be considered as possible rather than certain.
- Recycling of material seems probable, if not even likely. As such, copper artefacts may actually contain copper from various sources that may be difficult to distinguish in ex-post analysis.
- If copper ores occur in close proximity to uranium ores, their distribution of lead isotopes will vary widely due to radioactive exposure. Such ores are very difficult to identify. This concerns, among others, ores from Wales, Cornwall, Brittany, the Massif Central, the Erzgebirge and some parts of the Harz mountains (http://www.aditnow.co.uk/documents/personal-album-272/Copper-deposits-in-south-west-England.pdf). Thus, the fact that the a/m places have not been identified as copper sources does not necessarily mean they were not producing and trading copper in ancient times.
- It has been commonly assumed that all impurities stem from the copper, while the tin used for alloying was pure. This relates to the fact that pure tin deteriorates naturally (below 13°C it gradually becomes a powder), while tin with a lead content above 0.5% doesn't. As tin ingots have only been found in exceptional cases, it has thus been assumed that most of the traded tin was so pure that it has deteriorated in the meantime.
However, recently tin ingots with 1.5% lead content have been found in the Tollense river in Mecklenburg (http://www.researchgate.net/publica...om_the_Tollense_valley_in_northeastern_German). Moreover, there is the possibility that, instead of refined tin, Cassiterite (SnO[SUB]2[/SUB]) ore has been used for smelting bronze. Cassiterite is very hard, washed out of the veins and accumulates in streams. Its tin weight content is quite stable around 79%. Thus, producing regions may have refrained from cumbersome refining, and shipped alluvial ore deposits instead. In any case, there is the possibility that bronze impurities did not only result from the copper, but also the tin used. Thus, a good part of the results published so far, especially those on bronzes with high tin content, may require review as concerns the possibility of lead input from tin.
In summary, this is still very much work in progress, and it is advisable to treat findings with some care.