Bronze Age Copper Ores of the British Isles: Rethinking the Role of Trace Element Analysis of Artifacts by Karen M. Spence (original) (raw)
Journal of Archaeological Science, 2022
Since the mid-1970s a Bronze Age assemblage of metal objects has been recovered from the seabed off the south Devon coast at Salcombe, southwest England. The assemblage spans two suspected shipwreck events and comprises nearly 400 pieces of raw materials and finished artefacts, primarily in copper, tin, bronze and gold. Among these are 280 copper and 40 tin ingots, by far the largest discovery of Bronze Age ingots in either metal from northwestern Europe. Research in recent years revealed the microstructural and chemical nature of the ingots and enabled some preliminary conclusions on the metals trade in Europe in the Later Bronze Age. The present study aims to extend this knowledge by determining the tin, copper and lead isotopic compositions of the ingots using HR-MC-ICP-MS. In addition, bronze artefacts (swords, rapiers, palstaves and weights) from the Salcombe site are included in the multi-proxy approach in order to investigate their history and the possible relationships between finished products and ingots. In combination with the available chemical data of previous studies, the current results of the tin metal show that most likely two tin sources in southwest Britain supplied the ore for their production. This also sheds light on Late Bronze Age tin ingots from Israel that share the same geochemical characteristics with one group of the finds from Salcombe. Although the tin in the bronzes is similar to the tin in the ingots, it is not certain that the latter were used to make the bronzes. Correlations of copper and tin isotopes and trace elements of the bronzes point to a mixing or even recycling of copper-tin alloys rather than the alloying of individual components of copper and tin. However, the copper ingots from the assemblage could have been an additional component in the mixing process given their impurity pattern and isotopic composition. At the same time, a close relationship between swords of the Rosnoën type and palstaves from the cargo is disclosed. Lead isotope ratios for their part suggest Sardinian and/or south Spanish copper ores as a source for both the copper ingots and the copper of the bronzes. This would mean long-distance metal trade in the Later Bronze Age in both cases and would provide new insights into the interpretation of the prehistoric networks in Europe.
Pollard, A. M., Bray, P., Gosden, C., Wilson, A., and Hamerow, H. (2015). 'Characterising copper-based metals in Britain in the first millennium AD: a preliminary quantification of metal flow and recycling', Antiquity 89.345: 697–713., 2015
For many years, archaeologists and archaeometallurgists have suggested that recycled copper might have constituted a significant component of the metal in circulation in Britain during the first millennium AD. They have generally failed, however, to suggest a way of observing and quantifying this phenomenon. Here the authors propose a new methodology to rectify this. A large new database of chemical analyses of British copper alloys dating from the late Iron Age to the early medieval period demonstrates the potential of their approach; it shows that significant and measureable changes occur in metal circulation at the beginning of the first century AD and in the early Saxon period.
Archaeometry
We present a new methodology for interpreting lead isotope data from archaeological copper alloy objects. It is not based on the conventional isotope ratio biplots, which were originally devised to allow the calculation of the geological age of the lead mineralization, but is derived from isotope mixing models, more often used for presenting strontium isotope data. We illustrate the method by reworking published data on Sardinian Nuragic oxhide ingots and copper alloy artefacts. While we confirm the consensus assumption that the oxhide ingot fragments found on Sardinia are isotopically consistent with Cypriot copper ores (although we see no isotopic reason to favour only Apliki, as originally suggested), we also show that there is evidence for mixing between local and ingot copper in some objects, which was previously not detected. More broadly, we suspect that the apparent mismatch between some source allocations for copper drawn from isotope geochemistry and the rest of the archaeological data in some cases might be due to mixed isotopic signals being incorrectly assigned to a specific source, and suggest that the method presented here will reduce the chances of this happening.
The seabed site of a probable Bronze Age shipwreck off the coast of Salcombe in southwest England was explored between 1977 and 1982 and from 2004 onwards. Nearly 400 objects including copper and tin ingots, bronze artefacts/fragments and gold ornaments were found, typologically dating either to c. 1300–1150 BC or 1000–800 BC. The 280 copper and 40 tin plano-convex ingots and ingot fragments represent the largest discovery , measured by total weight as well as by quantity, of plano-convex or bun ingots in northwest Europe. The Salcombe copper ingots provided a wonderful opportunity for the technical study of copper ingots in a probable shipwreck context, as opposed to terrestrial contexts of deliberate deposition. The chemical composition of 25 plano-convex copper ingots was determined using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Two artefacts from the site were also analysed for comparison with the ingots. Following the compositional analysis, a microstructural study was carried out on ten Salcombe copper ingots selected to cover those with different sizes, shapes and variable impurity levels using metallography and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS). All the analysed copper ingots are of unalloyed copper with low levels of impurities. Sulphide inclusions are present in all samples and bulk sulphur contents are of 0.32–0.79% in the ingots but lower in the artefacts. The Salcombe ingots were found to have a quite similar impurity pattern to the Hertford Heath (England) ingots (except for iron content). They are distinctly different from the Uluburun ingots, and, to a lesser degree, from Sardinian ingots. The results are inconclusive as to how the Salcombe ingots were made. On the one hand, the very low concentration of iron and the absence of cuprite inclusions suggest that the ingots were primary smelting products of the primitive smelting process rather than produced from re-melting or refining of primary smelting lumps. On the other hand, the dense metal with very low porosity suggests the product of refining and re-casting operations under reducing conditions. However, the small ingots are not likely to have resulted from breaking of large ingots. The chemical compositions of the Salcombe ingots point to British or Western European sources although the connection with other regions cannot be excluded for some of the ingots. Further studies including lead isotope analysis are needed to address the question of provenance of the copper ingots, which would contribute to the re-emerging debates surrounding the European Bronze Age metal trade.
In: The origins of metallurgy in Europe. Historical Metallurgy 47(1) pp.93-110.
Linking the Great Orme Bronze Age copper mine to British metalwork by analysing ores, copper prills from Pentrwyn and particles of bronze found in the mine is an ongoing project. This paper focuses on the smelting slags and prills recovered during the 2011 excavations from the Pentrwyn site, the only smelting site known from the British Bronze Age. They indicate the use of a simple smelting process which used secondary carbonate ores with only residual sulphides. The unusual slags are low in silica, like the ores, and lack any additives which resulted in only a small amount of glassy phase being produced. Hence, the copper prills must have been recovered by crushing, which matches the small size of the slag pieces. Lead isotope results link the slags to the Great Orme ores. The analyses of the copper prills show variable trace a proportion of British Bronze Age metalwork.
Prehistoric Copper Extraction in Britain: Ecton Hill, Staffordshire
Proceedings of the Prehistoric Society, 2013
Major investigations were undertaken of the Ecton Copper Mines, Staffordshire, following the discovery of hammerstones and a red deer antler tool dating to the Early Bronze Age during surface and underground exploration in the 1990s. Ecton Hill was surveyed, the distribution of hammerstone tools examined, and two identified sites of potential prehistoric mining close to the summit of the hill excavated in 2008 & 2009. Excavations at Stone Quarry Mine revealed no in situ prehistoric mining activity, but hammerstones and Early Bronze Age bone mining tools from upcast suggest that an historic mine shaft had intersected Bronze Age workings at around 10-25 m depth. On The Lumb one trench revealed evidence for medieval lead mining, while another examined the lowest of four primitive mines associated with cave-like mine entrances along the base of a small cliff. Evidence for prehistoric mining was recorded within a shallow opencut formed by during extraction of malachite from a layer of mineralised dolomite. Traces of the imprint of at least 18 bone and stone tools could be seen and seven different types of working were identified. Most prehistoric mining debris appears to have been cleared out during the course of later, medieval-post-medieval prospection; some bone and stone tools were recovered from this spoil. The tip of a worn and worked (cut) antler tine point was the only such mining tool found in situ at this site but nine tools were radiocarbon dated to c. 1880-1640 cal BC. Bayesian modelling of the dates from both sites probably indicates mining over a much briefer period (perhaps 20-50 years) at 1800-1700 cal BC, with mining at Stone Quarry possibly beginning earlier and lasting longer than on The Lumb. A single date from The Lumb suggests possible renewed mining activity (or prospection?) during the Middle Bronze Age. The dating of this mining activity is consistent with the idea that mining and prospection moved eastwards from Ireland to Wales, then to central England, at the beginning of the 2nd millennium BC. At Ecton the extraction of secondary ores may have produced only a very small tonnage of copper metal. The mine workers may have been Early Bronze Age farmers who occupied this part of the Peak District seasonally in a transhumant or sustained way.