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Tainted ores and the rise of tin bronzes in Eurasia, c. 6500
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Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago Miljana Radivojević, Thilo Rehren, Julka Kuzmanović-Cvetković, Marija Jovanović and J. Peter Northover Antiquity / Volume 87 / Issue 338 / December 2013, pp 1030 - 1045 DOI: 10.1017/S0003598X0004984X, Published online: 02 January 2015
Link to this article: http://journals.cambridge.org/abstract_S0003598X0004984X How to cite this article: Miljana Radivojević, Thilo Rehren, Julka Kuzmanović-Cvetković, Marija Jovanović and J. Peter Northover (2013). Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago. Antiquity, 87, pp 1030-1045 doi:10.1017/S0003598X0004984X Request Permissions : Click here
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Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago Miljana Radivojevi´c1,2 , Thilo Rehren3 , Julka Kuzmanovi´c-Cvetkovi´c4 , Marija Jovanovi´c5 & J. Peter Northover6 The earliest tin bronze artefacts in Eurasia are generally believed to have appeared in the Near East in the early third millennium BC. Here we present tin bronze artefacts that occur far from the Near East, and in a significantly earlier period. Excavations at Ploˇcnik, a Vinˇca culture site in Serbia, recovered a Belgrade piece of tin bronze foil from an occupation layer dated to the mid fifth millennium BC. The discovery prompted a reassessment of 14 insufficiently contextualised early tin bronze artefacts from the Balkans. They too were found to derive from the smelting of coppertin ores. These tin bronzes extend the record km 100 0 N of bronze making by c. 1500 years, and challenge the conventional narrative of Eurasian metallurgical development. Keywords: Eurasia, Serbia, Bulgaria, Ploˇcnik, Belovode, fifth millennium BC, Vinˇca culture, copper, tin, bronze, metallurgy, compositional analysis Supplementary material is provided online at http://antiquity.ac.uk/projgall/radivojevic338/
Introduction From their earliest appearance in the third millennium BC to their widespread adoption during the second millennium BC, tin bronzes had a significant impact on Bronze Age societies in Eurasia, including major changes in the economic, political and social lives of 1 2 3 4 5 6
UCL Institute of Archaeology, 31–34 Gordon Square, London WC1H 0PY, UK (Email: [email protected]) National Museum in Belgrade, Trg Republike 1a, 11 000 Belgrade, Serbia UCL Qatar, a partner of Hamad bin Khalifa University, PO Box 25256, Doha, Qatar (Email: [email protected]) Museum of Toplica, Ratka Pavlovi´ca 11, 18 400 Prokuplje, Serbia (Email: [email protected]) Museum of Vojvodina, Dunavska 35, 21 000 Novi Sad, Serbia (Email: [email protected]) Department of Materials, University of Oxford, Begbroke Science Park, Oxford OX5 1PF, UK (Email: [email protected])
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consumer communities (e.g. Harding 2000; Anthony 2007; Kuz’mina 2008). Bronze is an alloy of copper and other metals with copper as the major component. Tin is the most common alloying agent but other bronzes may incorporate arsenic, aluminium, silicon or phosphorus (Caron et al. 2004). To avoid ambiguity it has become common practice in archaeology to call the alloy of copper with tin ‘tin bronze’ and the alloy of copper with arsenic ‘arsenical copper’. Extensive scholarship has been devoted to the ‘tin question’ in pursuit of the sources of tin, the evidence for its production and the trade routes by which it travelled across the Old World (Muhly 1973; Pigott 1999; Yener 2000; Giumlia-Mair & Lo Schiavo 2003). The earliest known tin bronze artefacts, mostly pins or flat axes, have been discovered in Mesopotamia and Anatolia, and date to the early third millennium BC (Stech & Pigott 1986; Weeks 1999; Begemann et al. 2003; Helwing 2009). These objects contain up to 10 weight per cent (wt%) tin, and this is commonly thought to be due to the intentional addition of tin ore (cassiterite, SnO2 ) to copper ores (co-smelting) or copper metal (cementation) (e.g. Cleziou & Berthoud 1982). These areas of early tin bronze consumption, however, lack significant tin sources. A quest for the tin source in Anatolia prompted extensive research on archaeological, geological and textual evidence, and likely origins were announced and subsequently dismissed in heated academic debates (Muhly 1993; Yener et al. 1993). More recently, multiple cassiterite sources exploited during the Bronze Age have been identified in modern Iran, Afghanistan, Uzbekistan and Tajikistan (Weisgerber & Cierny 2002; Nezafati et al. 2006, 2011; Pigott 2011; St¨ollner et al. 2011). Alongside the important issue of the sources is the question of how the early production of tin bronze fits into the traditional narrative of the evolution of Eurasian metallurgy. This narrative seeks to follow a relatively simple, unilinear model of the inception and development of metallurgy from a single region. It begins with copper minerals and the first working of native copper in the Neolithic, which led to small-scale copper smelting from oxidic ores in the Chalcolithic. By the end of this period and well into the Bronze Age, mixing of ores was practiced to produce arsenical copper, followed by the large-scale smelting of sulphidic copper ores. By the Middle to Late Bronze Age, pure copper was alloyed with tin metal to mass-produce tin bronze. Iron production eventually emerged by the end of the Late Bronze Age (e.g. Wertime 1964). While this narrative is sufficient for interpreting broader consumption patterns that did indeed evolve in this order, a higher-resolution regional perspective on metallurgical production and innovation modulates this established sequence considerably, as, for instance, in the Middle East (Thornton 2009), or in the Americas, where the evolutionary trajectory of metallurgy is entirely independent of its development in the Old World (Lechtman 1980; Ehrhardt 2009). Multiple origins must therefore be envisaged. The hypothesis of a single origin for Eurasian metallurgy (most recently Roberts et al. 2009) has been challenged by the discovery of copper smelting evidence some 7000 years old at a location outside the Near East: Belovode, a Vinˇca culture settlement in eastern Serbia (Radivojevi´c et al. 2010). Here, smelting of metal continued for several centuries alongside substantial malachite bead production, exploiting multiple local copper sources. Compositional analyses indicate a clear distinction between the malachite deposits exploited for bead making and those for copper smelting. Pure green malachite was favoured for bead making, while black-and-green ores, a copper and manganese mineral paragenesis, were C
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Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago
used for copper metal extraction. Such consistent selection indicates a good understanding of the technological properties of various raw materials. The manganese content in copper minerals, indicated by the black-and-green colour composite, had a decisive role in selecting the best copper source for making metal. The pure green bead minerals were, on the other hand, sought for the strong symbolism of their colour (cf. Bar-Yosef Mayer & Porat 2008). The colour dichotomy of the black-and-green ores used for smelting and of pure green minerals processed for bead making makes the former appear as stained or ‘tainted’ ores, which is how they are termed in our research. Here we present analyses of a tin bronze foil, from the Vinˇca culture site of Ploˇcnik in southern Serbia, that may have been used for wrapping a ceramic vessel (Figure 1A). The site of Ploˇcnik has been solely occupied by the Vinˇca culture, and no later cultural intrusions have, thus far, been documented (e.g. Sˇ ljivar et al. 2012). The tin bronze foil was excavated from an undisturbed context, on the floor of a dwelling structure next to a copper workshop (Sˇ ljivar & Kuzmanovi´cCvetkovi´c 2009; Sˇ ljivar et al. 2012: 33). It lay approximately 1m from a fireplace, and was found among several late Vinˇca culture pottery vessels (Figure 2). This securely contextualised find comes from a single undisturbed occupation horizon that has been dated to c. 4650 BC (Bori´c 2009: 214). According to the field evidence, the date is a terminus ante quem for the Ploˇcnik Figure 1. Fifth millennium BC tin bronze artefacts from foil. The tin bronze foil from the site of Vinˇca culture sites in Serbia: (A) tin bronze foil from Ploˇcnik, Ploˇcnik is therefore the earliest known tin securely dated to c. 4650 BC; (B) tin bronze ring from bronze artefact anywhere. Gomolava, tentatively dated to the mid fifth millennium BC.
Early tin bronzes in the Balkans: background The Ploˇcnik foil is not the only find of early tin bronze artefacts in the Balkans. Fourteen other early tin bronze artefacts were discovered during the last century, but these were either poorly dated or insufficiently contextualised beyond their broad ‘Chalcolithic’ assignation (Chernykh 1978; Ottaway 1979; Tasi´c 1982; Pernicka et al. 1993). A piece of copper-tin slag deposited in one of the burials in the late fifth millennium BC cemetery of Zeng˝ov´arkony in Hungary (Glumac & Todd 1991) represents further evidence of tin use in this period; however, its context has been questioned (Pernicka et al. 1997). The Ploˇcnik foil thus is the only securely dated artefact among the entire Balkan early tin bronze assemblage. Twelve of the previously analysed Chalcolithic finds originate from Bulgarian sites (Ruse, Karanovo, Gradeshnica, Smjadovo, Zaminec and Bereketska Mogila), and two from Serbian C
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Figure 2. The context of the tin bronze foil from Ploˇcnik. The rectangular outline of the dwelling structure is indicated by the red burnt sediment; the foil was discovered in its south-eastern corner, among a dozen pottery sherds, and close to the oven.
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sites (Gomolava and Lazareva Cave) (Figure 3). They consist of awls, rings, needles, borers and a rod and have tin concentrations from 1–10wt%, followed consistently by significant levels of lead, arsenic, nickel, cobalt, iron and gold (Table 1). Although the exact concentrations of these elements vary widely from sample to sample, they appear qualitatively similar, which suggests an origin from similar types of ores. They are typologically similar to contemporary copper finds, and some of them directly match counterparts in pure copper from the fifth millennium BC Balkans. All of the objects were discovered in multilayered sites within disturbed Chalcolithic occupations, except a ring from Ruse (ASM 10882) that is reported to come from a child’s burial belonging to an undisturbed Chalcolithic horizon. The cultural and chronological attribution of these tin bronzes was tentatively assumed to be Chalcolithic on the basis of their distinctive composition, different from later bronzes, and their limited quantity (Chernykh 1978: 81). Furthermore, no other tin bronze artefacts are known in the Balkans before the third and second millennia BC (Chernykh 1978; Schickler 1981; Pernicka et al. 1997; Pare 2000), making it very unlikely that these early finds are intrusions from later layers.
Results Two artefacts were newly analysed for this study: the foil from Ploˇcnik (no. 63) and the Gomolava ring (no. 212) (Figure 1B), previously studied by Ottaway (1979); our methodology is reported in the online supplementary material. The Ploˇcnik sample has on average 11.7wt% tin (Table 1), together with lead, nickel, and iron at levels of between one tenth and half of one per cent each. The Gomolava ring has only 8.5wt% tin, but significantly higher levels of lead, arsenic, antimony and nickel, all between a quarter of one per cent and one per cent. Sulphur and selenium concentrations are relatively high in both samples. The high level of metallic iron in the Ploˇcnik foil demonstrates that this is freshly smelted metal, not re-melted during alloying (Craddock & Meeks 1987), while the presence of significant levels of antimony and arsenic in Gomolava 212 is typical of copper smelted from fahlerz ores (or fahlores). Both objects have a completely homogenised structure (Figure 4), which for tin bronzes above 8wt% tin requires annealing temperatures in the range of 500–800◦ C (Scott 1991). The foil is fully recrystallised, with grain sizes of c. 0.2mm (Figure 5). A single annealing twin in the microstructure is probably a result of cold working and prolonged annealing, which left the foil soft enough to be wrapped around a (presumably) ceramic vessel. The Gomolava ring has an incompletely recrystallised structure with much smaller grain size (c. 0.025mm) indicating several cycles of working and annealing (Figure 6). This is consistent with a high degree of cold reduction, estimated at between 60 and 80 per cent (Rostoker & Dvorak 1990) on the basis of elongated sulphur-rich inclusions. The incompletely recrystallised structure may indicate that the last annealing process before final working was not carried through to completion, leaving the metal in a work-hardened state, suitable for use as jewellery. In summary, the samples consist of chemically complex copper metal rich in tin and a range of minor and trace elements. They were made using different working sequences, carefully C
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ASM 12138 ASM 10686 HDM 2733 Average
HDM 2720 ASM 12043 ASM 12103 ASM 12105 ASM 12051 HDM 1330 Ploˇcnik 63 Average Gomolava 212 ASM 10853 HDM 2046 (ASM 10875) ASM 10863 ASM 10882 Average
Smjadovo Karanovo Bereketska Mogila Bereketska Mogila Karanovo Lazareva pe´cina Ploˇcnik First group (stannite) Gomolava Ruse Ruse
Ruse Ruse Second group (high-tin fahlore) Bereketska Mogila Gradeshnica Zaminec Third group (low-tin fahlore) Typical EC/MC (n = 40)
Sample label
Site of origin
rod awl borer
borer ring
ring awl borer
borer ring needle awl needle borer sheet
1.0 4.5 3.1 2.9 0.005
100
10.0 7.0 7.8
8.6 7.0 6.0 10.0 7.0 7.1 11.7 8.2 8.5 6.0 7.3
96.8 94.3 95.9 95.8
88.4 92.1 89.0
90.5 92.5 92.9 89.6 92.1 98.0 87.4 91.8 89.4 89.2 86.0
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0.04
0.06 0.35 0.26 0.22
0.40 0.50 0.44
0.34 0.20 0.35 0.01 0.07 0.02 0.03 0.15 0.35 0.60 0.35
0.04
0.02 0.01 0.04 0.02
0.07 0.07 0.13
0.44 0.05 0.70 0.30 0.20 0.06 0.12 0.27 0.005 0.20 0.31
0.001
nd 0.003 0.002 0.003
0.02 0.04 0.023
0.01 0.02 0.012 0.04 0.01 0.0003 0.07 0.02 0.025 0.015 0.016
0.01
0.008 0.04 0.06 0.036
0.40 0.10 0.25
0.02 0.15 0.02 0.06 0.50 0.004 0.16 0.13 0.25 0.20 0.28
0.04
0.02 0.05 0.108 0.06
0.03 0.03 0.04
0.016 0.004 0.002 0.002 0.0003 0.007 nd 0.005 0.08 0.04 0.03
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0.001
0.0029 0.0030 0.0014 0.002
0.030 0.003 0.008
0.002 0.001 0.003 0.003 0.003 0.004 0.016 0.004 0.002 0.001 0.003
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0.01
0.07 0.50 0.33 0.30
0.50 0.06 0.30
0.020 0.005 0.010 nd nd 0.013 nd 0.01 0.45 0.20 0.30
0.013
2.0 0.2 0.14 0.78
0.18 0.05 0.92
0.05 0.02 0.005 0.004 0.15 0.006 0.40 0.09 0.82 3.5 0.05
Object Cu wt% Sn wt% As wt% Fe wt% Co wt% Ni wt% Ag wt% Sb wt% Au wt% Pb wt%
Table 1. Compositional data for early tin bronze artefacts from the Balkans, given in wt%. Data for artefacts other than Ploˇcnik (63) and Gomolava (212) taken from Chernykh (1978: 112, 339–52) and Pernicka et al. (1993: 10, tab. 3; 1997: 121–26, tab. A1). Compositional patterns distinguished three separate groups, based on the potential ores used for their production: predominant stannite; fahlore with stannite (high-tin fahlore); and fahlore with some stannite (low-tin fahlore). The bottom row represents an average of 40 contemporary copper metal artefacts from the Early (EC) and Middle Chalcolithic (MC), based on data from Pernicka et al. (1993: 190, tab. 3; 1997: 147–48, tab. A1), demonstrating that the trace element signature of the bronzes is unlikely to originate from the copper.
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Tainted ores and the rise of tin bronzes in Eurasia, c. 6500 years ago
Figure 3. The fifth millennium BC ‘polymetallic’ map of the Balkans, showing locations of sites mentioned here. Symbols indicate the type of metal in artefacts discovered at these sites. Base map courtesy of M. Milinkovi´c, Faculty of Philosophy, Belgrade; adapted by Lj. Radivojevi´c.
adjusted to the different properties required by the two objects, and with considerably higher annealing temperatures than those used for pure copper. This demonstrates that the metal smiths understood clearly the specific properties and requirements of tin bronze, as opposed to the more commonly used copper.
Tin bronzes in the Balkans: comparative analysis The Ploˇcnik and Gomolava objects are similar in composition to 13 previously analysed early tin bronzes from Bulgaria and Serbia. Compared to contemporary Early and Middle Chalcolithic (EC/MC) Bulgarian copper artefacts, levels of iron, cobalt, nickel and arsenic C
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are on average about one order of magnitude higher, and those of antimony and lead up to two orders of magnitude higher (Table 1). Such a trace element pattern is not found in later tin bronzes, and is unlikely to originate from the addition of tin metal or cassiterite to ordinary copper; most cassiterite deposits and the tin smelted from them are very low in these base metals. Instead, the trace element pattern indicates the use of other, more complex ores for the production of these objects. The analyses fall into three groups (Table 1). Traditionally, copper with significant impurities of arsenic, antimony, silver and nickel is thought to originate from fahlore smelting (Otto & Witter 1952; Merkl 2010). Fahlore copper, however, does not normally contain more than a few tens of ppm tin. Instead, Figure 4. Photomicrographs of unetched sections of Vinˇca the tin in these early bronzes is thought culture tin bronzes: (A) the Ploˇcnik foil; (B) the Gomolava to originate from stannite, Cu2 FeSnS4 , a ring. Both samples show a homogenised structure with grey sulphur-rich inclusions. copper-tin mineral structurally similar to chalcopyrite, and visually a dark metallicgrey like fahlore. The three compositional groups presumably originate from a copper ore containing varying amounts of fahlore and stannite, probably mixed with other metal-rich minerals. The association of primary copper deposits, such as chalcopyrite, with both stannite and fahlore is not uncommon in sulphidic ore bodies in tin-rich provinces (Ramdohr 1980: 549–62; see also online supplementary material), and tin deposits are widespread throughout the Balkans (Glumac & Todd 1991). Ore batches used as a charge in the smelting process, retrieved from such ore deposits, would inevitably vary in their relative proportions of chalcopyrite, stannite and fahlore, resulting in the variable composition of the alloys seen here. The high sulphur content in both of the samples that were studied microscopically further indicates the sulphidic nature of the primary ore source, even if the smelted charge may have been dominated by secondary minerals formed from these sulphides. Thus, the three groups are tentatively labelled stannite bronze, high-tin fahlore bronze and lowtin fahlore bronze, indicating the possible ore types that could have underpinned their production. The next horizon of bronzes in Serbia, dated to the third millennium BC, is characterised by significant arsenic (As) content (on average c. 1wt%, and reaching up to 4wt%), alongside traces of tin (Sn) (