bs_bs_banner Archaeometry ••, •• (2014) ••–•• doi: 10.1111/arcm.12104 T H E C O M POSIT ION AND M ICRO S TR U C TU R A L VA R I ATI O N OF T H E B R ONZ E AGE M E TAL OR N A MEN TS FR O M LO WER S I LE SI A ( SOUT H-W E ST P OL AND): C H EMI C A L A N A LY TI C A L AND ARCHAE OL OGIC A L A S PEC TS * J. PUZIEWICZ,1† J. BARON,2 TH. NTAFLOS3 and B. MIAZGA2 1 Institute of Geological Sciences, University of Wrocław, pl. M. Borna 9, 50-205 Wrocław, Poland 2 Institute of Archaeology, University of Wrocław, ul. Szewska 48, 50-139 Wrocław, Poland 3 Department of Lithospheric Research, University of Vienna, Althanstraße 14, 1090 Wien, Austria Metal ornaments from Únětice (Mierczyce, Tomice, Jordanów and Opatowice) and Urnfield culture (Szprotawa, Żarek and Wrocław Żerniki) sites in south-west Poland are made of bronze of varying composition, with the exception of the early Bronze Age Przecławice site, where the copper items are found in graves from stages III/IV. The combined XRF and electron microprobe study of 37 ornaments (mostly pins) shows that those excavated from Únětice culture graves usually consist of cored dendrites, plus a Sb-rich phase in some. The copper objects from Przecławice correspond in composition to the East Alpine Copper or to the Ösenring copper and were produced from fahlore. Those from the Urnfield culture sites consist of homogeneous bronze. The Únětice culture ornaments were produced with little control of the effect of varying bronze composition on its microstructure. The results of XRF analyses of heterogeneous metal artefacts vary depending on the proportion of phases in the analysed site, and should be combined with micrometre-scale analytical data and microstructural information yielded by electron microprobe methods. The same refers to deeply weathered or corroded objects made of homogeneous metal, which contain irregularly dispersed decomposition products. KEYWORDS: ÚNĚTICE CULTURE, URNFIELD CULTURE, BRONZE AGE, SOUTH-WEST POLAND, BRONZE, COPPER, MICROSTRUCTURE, CHEMICAL COMPOSITION INTRODUCTION Knowledge about the chemical composition and internal microstructure of prehistoric metal artefacts is essential in their characterization. The chemical composition (major and trace elements) as well as the lead isotopic ratios are commonly studied in bronze and copper artefacts in order to gain knowledge about the ore provenance and the applied technology (e.g., Pernicka 1999 and references therein). Methods that allow chemical analyses without destruction of the studied item are obviously preferred during archaeological studies. However, in order to get information on the microstructure of the metal, it is usually necessary to prepare a section of the metal and this requires the cutting of small fragments of the artefacts. We studied Bronze Age metallic ornaments from south-west Poland by means of XRF and electron microprobe methods. The first of these requires minimal action on the studied artefact (it is necessary to clean the analysed spot), whereas the other requires the preparation of metal *Received 21 September 2013; accepted 5 February 2014 †Corresponding author: email jacek.puziewicz@ing.uni.wroc.pl © 2014 University of Oxford 2 J. Puziewicz et al. sections. XRF analysis by machine, as applied by us, yields the composition of a spot the size of which is slightly less than 1 mm2, whereas the electron microprobe method is able to analyse a 1 μm spot and to show the microstructure of the analysed site on the scale of few micrometres. Our intention was (1) to compare the results yielded by the two methods, which operate at different scales, and (2) to obtain microstructural and compositional data on the possibly broad spectrum of artefacts coming from the area of Lower Silesia in south-west Poland. We have studied the artefacts of the Únětice culture, found at five sites in south-west Poland, and those from the younger Urnfield culture (three sites). A significant part of the study was devoted to ornaments coming from the Przecławice cemetery in south-west Poland, 30 km south of Wrocław (Fig. 1). The cemetery is located in a region of very dense early Bronze Age settlements; however, the site is unique because the graves come from all stages of the Únětice culture. The other studied sites are Mierczyce, Tomice, Jordanów and Opatowice (the Únětice culture) plus Figure 1 The studied Bronze Age sites in south-west Poland. © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 3 Żarek, Wrocław Żerniki and Szprotawa (the Urnfield culture). Our study shows that the XRF analyses are representative only for artefacts made of homogeneous metal. If the bronze or copper is heterogeneous and consists of two or more phases, the combination of both XRF and the electron microprobe method is necessary to get reasonable results. ANALYTICAL METHODS Small (1–2 mm) fragments of the studied artefacts were cut off, mounted in resin (Araldite) rings and polished. The polished surfaces were examined using a reflected light petrographic microscope and studied by the electron microprobe method and by X-ray fluorescence. The choice of analytical points for the electron microprobe analyses was done in the BSE (backscattered electron) image, which provided detailed microstructural and compositional information on the studied phases. We used both polished sections and cleaned spots on the artefacts for the XRF analyses. To study the compositional variation in bronze and copper artefacts, we analysed for Cu, Sn, Sb, As, Ni, Fe and Pb. We also included Al, Si, Zn and S in the electron microprobe analytical protocol and Ag in the XRF one. This was to verify samples for contamination during polishing (Al) or to analyse the weathering phases and/or sulphide droplets using the same machine set-up. One set of electron microprobe analyses revealed the Al content (up to 0.6 wt%) in the analysed metals that had been polished using Al powder; the use of diamond powder eliminated that effect. The CAMECA SX100 electron microprobe in the laboratory of the Department of Lithospheric Research at the University of Vienna, Austria was used to analyse the major element composition of phases. We used typical conditions for microprobe analyses, with pure metals as standards, except for Pb, Sb and As (standards, respectively, PbO, InSb and GaAs). Counting times of between 20 and 40 s (peak) were used, except for As, for which the peak counting time was 80 s. This assured the following detection limits (approximate values in ppm): Al, Si, 330; S, 380; Sb, 2200; Fe, 360; Ni, 530; Cu, 2000; Zn, 830; As, 900; Sn, 1400; Pb, 1450. The Zn, Fe, Pb and S occur in concentrations <0.09 wt% in the studied artefacts, except for the higher contents of S in sulphide droplets. The ‘bulk’ metal composition was determined by XRF (using a Spectro Midex X-ray fluorescence spectrometer with energy dispersion), equipped with a molybdenum X-ray lamp, with an excitation energy of 44.6 kV, and a Si Drift Detector (SDD) with 150 eV resolution. For calibration, Certified Reference Material BCR 691 of the Institute for Reference Materials and Measurements was used. The analysed spot size was ∼0.7 mm. The detection limits were as follows: Sn, Sb, 500 ppm; Pb, 200 ppm; Fe, 250 ppm; Ni, 150 ppm; Cu, Zn, 100 ppm; As, 50 ppm. CULTURES AND SITES The Únětice culture, with its characteristic pottery and metalwork, existed across large parts of Central Europe (e.g., Machnik 1977; Zich 1996; Bartelheim 1998). Its relative chronological division is based on P. Reinecke’s system (covering early Bronze Age stages A1 and A2) and is composed of several internal stages, with the most developed one called ‘the classical stage’. The earlier stages (between two and four, depending on areas studied) are dated to 2350–1950 bc, while the classical one is dated to 1950–1700 bc. In some areas, a post-classical stage was also identified and dated to 1700–1600 bc (e.g., Vandkilde 1996, 140–2). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 4 J. Puziewicz et al. The most common Únětice site types are small cemeteries, containing only a few graves in the older stages and larger cemeteries in the classical stage. Inhumation graves with bodies placed in the foetal position were a prevalent form of disposal; however, cremation graves (in both pit and urn versions) occur at the same cemeteries (Kadrow 2001, 121–3). All artefacts analysed in this study come from inhumation cemeteries. Cemeteries of cremated burials deposited as urnfields are a pan-European phenomenon starting about 1350–1300 bc; however, cremation graves had been common in many parts of Bronze Age Europe before that date (for more on a cremation rite and the origins of the urnfields, see Mierzwiński 2012). In Poland, urnfields are considered as an essential component of the so-called ‘Lusatian culture’ that lasted up to about 500 bc; however, this term has been subject to criticism (e.g., Gediga 1984). The analysed artefacts come from graves of varying chronology. The sites of Żarek and Szprotawa are older, while Wrocław Żerniki represents the late stages. The sites and sample contexts are briefly presented in what follows. Most of the sites are located on the alluvial plane of Lower Silesia, which is filled with fluvioglacial deposits, overlying Neogene sands and clays with brown coal layers. Isolated sand/gravel hills occur in the southern part of the plane, close to the border with the Fore-Sudetic Block, in which the Variscan crystalline basement is uplifted and covered by thin (tens of metres) younger deposits. The sites of Jordanów and Tomice are situated in the Śle˛ża Massif, in the Fore-Sudetic Block. The Śle˛ża Massif is the uplifted block of crystalline basement, consisting partly of granites and partly of ophiolitic sequences (gabbros, serpentinites and metabasalts). Jordanów and Tomice are located on serpentinites, and the former is known for the occurrence of nephrite. Únětice sites Przecławice The site of Przecławice is located 0.9 km south of a contemporary village of the same name, about 30 km south of Wrocław in Poland (Fig. 1). The cemetery, which lies on a north-western slope of a well-defined hill (Fig. 2), was discovered in 1975, when four skeletons were found in course of gravel exploitation in an elongated ∼200 m long pit. Excavations were initiated in the same year by Irena Lasak from the Institute of Archaeology, University of Wrocław, Poland, to protect the site from further destruction. A total area of 2050 m2, containing 51 graves, was explored in the course of a four-season campaign (Lasak 1988). Although the cemetery is located in a region of very dense early Bronze Age settlement, the site is unique due to its wide chronology and broad spectrum of finds. The excavations provided a jar grave and well-preserved coffin burials. The properties of the graves and the artefacts—mostly pottery and several metal items—allow the site to be dated to the early Bronze Age, thus representing five stages of the Únětice culture. Two 14C dates obtained from two graves at Przecławice (1675 ± 75 and 1545 ± 45 bc) represent the youngest stage of the site use (Lasak 1988). To distinguish between graves of different ages, we follow the chronology defined by Lasak (1988), which was based on the studies of Moucha (1963) and Tichelka (1960). These authors defined the relative chronology based on material remains attributed to the Únětice culture. However, many graves contained grave goods of mixed chronological indicators, hence situating them in the transitional periods. All the sampled artefacts come from variously preserved and furnished skeleton graves dated to various stages of the site use (for details, see Table 1 and Fig. 3). Sampling was not possible from the stage V (the so-called ‘classical’ stage) items. The individuals were buried in a coffin (grave 12) or lain/wrapped in matting made of organic materials (graves 17, 18 and 33). According to © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 5 Figure 2 The morphological situation of the Przecławice site and details of the excavated area. The numbers refer to the graves described in Table 1 (modified from Lasak 1988). early Bronze Age tradition, the bodies were arranged in the foetal position along the north–south axis and this rule most probably also applies to the poorly preserved graves (17 and 18). Since the sample preparation for analyses is destructive, we decided to sample only poorly preserved—that is, already broken—small items (rings and beads) usually located near the skulls © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 6 Sample no. Grave no. An archaeological overview of the studied artefacts from the Przecławice site Sampled artefact Context Relative chronology Grave goods (including sampled ones) Anthropological data Willow leaf shape ring, 2.5 cm in diameter Two tubular beads, 1.2 and 1.3 cm long, 0.6 cm in diameter Northern part of a coffin, between two vessels South-eastern part of layer of dark brown soil—probably remains of a coffin or organic lining of the grave pit Southern part of layer of dark brown soil—probably remains of a coffin or organic lining of the grave pit, by the skull At the skull UC II/III Three vessels, metal ring UC I Two vessels, lump of ochre, four metal beads, two stone beads Two Infantes I (aged 1–2 and 5–6), aligned north–south Infans I (6 months) UC Two fragments of metal rings, piece of worked antler, one vessel Infans I (6 months) UC III/IV Female Maturus (aged 40–45) At and beneath the skull UC III/IV Five small and poorly preserved metal rings, two large metal rings (one incomplete), one metal pin, four vessels (one containing cattle scapula and two ribs) Three vessels, one large and three small metal rings At the skull, in the layer of dark brown soil—probably remains of a coffin or organic lining of the grave pit UC III/IV PZ4 12 PZ3, PZ11 17 PZ2, PZ2a 18 Two fragments of two incomplete rings of various sizes PZ5, PZ6 31 Two small rings, ∼1.5 cm in diameter PZ1, PZ7, PZ8, PZ9 32 PZ10, PZ12 33 One large and three small rings (diameters: 1.2, 1.5, 3 cm) Open ring, 1.3 cm in diameter; ring, 1.8 cm in diameter Four vessels, two bone pins, one metal pin, four poorly preserved metal rings, four vessels Female Iuvenis (aged ∼20) Iuvenis (aged 20–22) J. Puziewicz et al. © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Table 1 Bronze Age metal ornaments from Lower Silesia 7 Figure 3 The archaeological contexts of artefacts from the Przecławice site. The scale bars refer to a grave, pottery and non-pottery artefacts and are common for all graves in the picture (modified from Lasak 1988). The numbers in circles refer those of studied artefacts (cf., Table 1). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 8 J. Puziewicz et al. of the buried individuals (Table 1 and Fig. 3). Owing to their location in the graves, they are believed to be parts of simple head decorations. Jordanów Little is known about this large site, composed of both Neolithic and Bronze Age graves: the results of excavations carried out in the 1930s have never been fully published, and a substantial part of the archaeological evidence was lost during the Second World War. Brief notes mentioned inhumation graves, ceramics and bronze rings (Sarnowska 1969, 267). Some artefacts and bones survived and recently one 14C date was obtained (3505 ± 35 bp; laboratory code Poz-43472, Marta Mozgała pers. comm.). Although it is not from the grave from which the sampled artefact comes, it confirms the late Únětice chronology of the site (1926–1741 bc cal). Tomice This site, which lies on a small hill 550 m north-west of the contemporary village of Tomice, was excavated during two campaigns in 1967–8. In the course of the excavation, Neolithic, Bronze Age and early medieval pits and graves were unearthed. The early Bronze Age cemetery, dated to the classical stage of the Únětice culture, consisted of 36 inhumations and three cremation graves and covered an area of 1200 m2. The complete results, including the archaeological and anthropological data, were published in 1973 (Romanow et al. 1973). All the sampled artefacts—three pins, ring and a fragment of a bracelet—come from five inhumation graves (Fig. 4). Opatowice Human bones and pottery have been unearthed on the Gallow Hill near the village of Opatowice since the late 19th century and professional archaeological excavations in 1895 revealed two complete inhumation graves. Documentation stored in the Wrocław Museum shows that the site comprised about 20 graves. The report on the site has never been published and the documentation was mostly lost during the Second World War. The analysed artefact comes from one of the graves, but any precise context remains unknown. Mierczyce The cemetery was discovered by chance and excavated in 1967. In total, 18 inhumation graves were unearthed in a small area (Kaletyn 1975). The bone materials are gone but the artefacts represent typical inventories of the classical stage of the Únětice culture. For this study, five artefacts from three graves were sampled (Fig. 5). Urnfield sites Wrocław Żerniki The site at Wrocław Żerniki was discovered by chance in 1925 but excavated in 2009 in advance of constructing the Wrocław motorway bypass. In total, 59 cremation graves were unearthed in the investigated area (Baron et al. 2010). A general chronology of the cemetery based on artefact studies covers late stages of the Bronze Age and early Iron Age (1100–700/600 bc). No absolute dating was possible due to poor preservation of the cremated bones and low collagen content. One artefact from this site, from an urn in grave 18, was analysed and dated to 900–700 bc. Żarek This site was investigated in the 1970s as a rescue excavation and the results have never been fully published; thus the total number of excavated graves is unknown and part of the materials are lost. Both a settlement and a cemetery were discovered and their chronology covers both various stages of the Bronze Age and early Iron Age (∼1300–700 bc). The sampled items © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 9 Figure 4 The archaeological contexts of artefacts from the Tomice site. The numbers in circles refer to those of studied artefacts (cf., Table 2). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 10 J. Puziewicz et al. Figure 5 The archaeological contexts of artefacts from the Mierczyce site. The numbers in circles refer to those of studied artefacts (cf., Table 2). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 11 come from three cremation graves excavated in 1977 and dated to early stages of the Urnfield culture (1300–1100 bc). Szprotawa Five urn graves were excavated in during a rescue survey in 2012. Several stray finds of fragmented vessels and cremated bones accompanied the graves. Two of the graves were furnished with four metal items, one in grave 2 and three in grave 4 (Fig. 6). The bones from these graves gave two similar 14C dates; that is, 2970 ± 35 bp for grave 2 and 2935 ± 30 bp for grave 4 (Table 2). These results correspond with the traditional, artefact-based chronology covering early stages of the Urnfield culture which, in this area, is dated to 1300–1100 bc (Lasak 2001, 30–3; Kaczmarek 2002, 290–1). THE MICROSTRUCTURE AND COMPOSITION OF THE ARTEFACTS Most of the studied artefacts are pins made of bronze. Besides copper and tin, some of them contain significant antimony, arsenic and nickel (see Tables 3–5 below). The silver content is <1 wt%, in many cases <0.1 wt%. The description presented in the following is based on the electron microprobe analyses. The XRF analyses are not used in the description but are included in Figures 8–12 below. Únětice culture, stages I and II/III The oldest ornaments (Únětice culture, stages I and II/III) available for this study come from the Przecławice site. Five small beads come from grave 17 in Przecławice, dated to stage I. They are covered by carapace of weathering products (Fig. 7 (a)) and consist of dendritic aggregates (cored dendrites) of composition B containing ∼10–15 wt% of Sn (Table 3) embedded in a ∼20–25 wt% Sn host A (Table 3, samples PZ3 and PZ11). The host is one of the most tin-rich compositions found in all of the analysed artefacts of the Únětice culture (cf., Figs 8– 11). In the first analysed bead, alloy A contains significant amounts of As and Sb, whereas alloy B is impoverished in those elements (Table 3 and Fig. 8). The metal forming the second analysed bead is very pure and contains practically no other elements except for Cu and Sn (Table 3, sample PZ11). The artefact coming from the Przecławice grave 12, dated to Únětice stage II/III, is homogeneous metal with small voids (Fig. 7 (b)), containing ∼10 wt% of Sn. The metal is pure and contains no significant amounts of Sb, As or other elements (Table 3, sample PZ4). Únětice culture, stages III/IV The artefacts coming from the graves in the Przecławice site dated to Únětice stage III/IV consist of copper (>95 wt% Cu) and contain no tin (Table 3, samples PZ1, PZ2, PZ4, PZ5, PZ7, PZ8, PZ9, PZ10 and PZ12). They differ in their Sb, As and Ni contents (Fig. 5). In most of them the metal is homogeneous: some of the ornaments contain scarce, micrometresize droplets of apparently immiscible Sb or Sn. Because of their small size, only qualitative analyses of these droplets by the EDS method were possible. Only one of the studied items exhibits a well-defined parallel arrangement of voids and intergrowths, suggestive of forging (Fig. 7 (c)). That one, plus another of stage III/IV, contain fine grains of copper sulphide (Cu2S; Table 3, sample PZ2). The following compositional types can be defined in those artefacts: © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 12 J. Puziewicz et al. Figure 6 The archaeological contexts of artefacts from the Szprotawa site. The numbers in circles refer to those of studied artefacts (cf., Table 2). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Table 2 Sample no. Grave no. Tomice site 14 34 15 31 16 28 17 21 18 22 Sampled artefact Context Relative chronology Absolute chronology Grave goods (including sampled ones) Anthropological data Pin Ring Pin Pin Pin Skeleton grave Classical stage of the Únětice culture 1950–1700 bc Two ceramic vessels, two metal pins Two ceramic vessels, six amber beads, metal rings, two metal pins, one flint arrowhead Male, adultus Maturus/senilis Two ceramic vessels, three amber beads, metal pin Infans I (7 years) Pin Ring Pin Bracelet Pin Skeleton grave Classical stage of the Únětice culture 1950–1700 bc Three ceramic vessels, metal pin Two ceramic vessels, metal pin, two hand stones Three ceramic vessels, metal pin, cow scapula Two ceramic vessels, metal pin, two metal bracelets Three ceramic vessels, metal pin, metal ring Infans I Adultus/maturus Adultus Infans II Female, maturus Pin Únětice culture 2350–7600 bc No data available No data available 20 Pin Classical stage of the Únětice culture 1950–1700 bc No data available No data available Żarek site 8 2 6 13 7 36 21 2 Pin Pin? Pin? Pin Cremation grave Early stage of the Urnfield culture 1300–1100 bc No data available Cremation grave Early stage of the Urnfield culture 2970 ± 35 bp (Poz-51497) 1312–1055 bc Three ceramic vessels, three pieces of metal pin Two ceramic vessels, metal item (pin?) No data available Four ceramic vessels, three pieces of metal pin 19 Jordanów site 163 Opatowice site Szprotawa site 4 23 24 4 4 Pin 2935 ± 30 bp (Poz-51500) 1261–1041 bc Four ceramic vessels, turned pin, piece of a pendant, head of a pin Adultus? c.900–800 bc Eight ceramic vessels Male, adultus Pin Piece of a pendant Wrocław Żerniki site 1Z 18 Pin Cremation grave Late stage of the Urnfield culture 13 © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 22 Adultus? Bronze Age metal ornaments from Lower Silesia Mierczyce site 5 7 7 7 10 3 1 2 5 4 An archaeological overview of the studied artefacts from Lower Silesia 14 J. Puziewicz et al. Table 3 Representative electron microprobe analyses of the studied Przecławice artefacts (wt%) Sample Description PZ3 Grave 17, bead A, dendrite composition A Grave 17, bead A, dendrite composition B Grave 17, bead B, dendrite composition A Grave 17, bead B, dendrite composition B Grave 12, ring Grave 31, ring Grave 32, ring A Grave 32, ring B Grave 32, ring C Grave 32, ring D Grave 33, ring A Grave 33, ring B Grave 18, ring Grave 18, ring, droplet of Cu2S PZ3 PZ11 PZ11 PZ4 PZ5 PZ1 PZ7 PZ8 PZ9 PZ10 PZ12 PZ2 PZ2 Cu Sn Sb As Ni 77.22 20.45 1.24 1.47 0.01 87.59 12.05 0.20 0.64 75.37 25.29 0.05 85.86 14.86 90.86 95.85 98.51 96.16 97.37 95.85 96.60 91.71 87.15 78.83 9.47 0 0.05 0.68 0 0.63 0.04 0.13 10.02 0.04 Pb S Total 0 0.04 100.43 0 0 0.01 100.49 0 0 0 0 100.71 0.04 0 0 0 0.01 100.77 0 0.52 0.32 1.22 1.19 0.98 0.82 2.17 1.37 0 0 2.75 0.53 0.36 1.11 0.68 0.25 1.24 0.28 0 0.05 0.45 0 1.13 0 1.56 1.20 4.40 1.62 0.02 0 0 0.08 0.09 0 0 0.02 0 0.05 0.17 0.02 0 0.02 0.01 0.02 0.01 0 0.01 0.03 20.39 100.40 99.57 99.51 99.65 99.69 99.71 98.93 99.66 100.52 99.45 (1) (Sb + Ni)-enriched—ring ‘B’ from grave 33; (2) As-enriched, Ni-poor—the ring from grave 31; (3) As-bearing, Ni-free—ring ‘C’ from grave 32; (4) mixed 1, containing small amounts of As, Sb and Ni—rings ‘B’ and ‘D’ from grave 32 and ring ‘A’ from grave 33; and (5) mixed 2, containing small amounts of As and Sb, but no Ni—rings ‘A’ and ‘C’ from grave 32. Únětice culture, classical stage The studied set of ornaments comprises those from Tomice (three pins, one ring and one bracelet), Mierczyce (four pins and one ring) and two pins from Jordanów and Opatowice. They consist mainly of copper and all except one contain significant amounts of tin (cf., Figs 10 and 11). The studied set of ornaments from Tomice contains two pins (graves 28 and 32) made of metal consisting of cored dendrites and Sn-rich eutectoid (Fig. 7 (d)). The end compositions of the cored dendrites contain approximately 11 and 6 wt% of tin, whereas the eutectoid contains 24 wt%; the Sn-richer compositions are also richer in Sb and As (Table 4, sample 16, and Fig. 10). They contain small amounts of Ni (∼0.10–0.20 wt%). Two ornaments—the ring from grave 31 and the pin from grave 22—are made of homogeneous metal containing ∼96 wt% of Cu and only 1 wt% of Sn, with small amounts of Sb and As (<1 wt% each) and traces of Ni (∼0.10 wt%, Table 4, analysis samples 15 and 18). The bracelet from grave 21 is made of homogeneous metal containing ∼93 wt% of Cu and 5 wt% of Sn plus some Sb and As (<1 wt% of each; Table 4, sample 17, and Fig. 10). The homogeneous metals contain sparse, small droplets of Ag-, (Ag + Bi)- or Sn-rich alloys. The pins from Mierczyce exhibit a dendritic microstructure formed of the Sn-enriched (Sn ∼ 9–11 wt%) and Sn-impoverished (Sn ∼ 6 wt%; Table 4, samples 4 and 2) compositions, © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 15 Bronze Age metal ornaments from Lower Silesia Table 4 Representative electron microprobe analyses of the studied artefacts from classical-stage Únětice culture sites and Urnfield culture sites (wt%) Sample Description 16 16 Tomice, grave 31, pin, eutectoid Tomice, grave 31, pin, Sn-rich dendrite composition Tomice, grave 31, pin, Sn-poor dendrite composition Tomice, grave 31, ring Tomice, grave 22, pin Tomice, grave 21, bracelet Mierczyce, grave 10, pin, Sn-rich dendrite composition Mierczyce, grave 10, pin, Sn-poor dendrite composition Mierczyce, grave 7, pin, Sn-rich dendrite composition Mierczyce, grave 7, pin, Sn-rich dendrite composition Mierczyce, grave 5, pin, eutectoid Mierczyce, grave 7, pin, eutectoid Mierczyce, grave 7, homogeneous ring Jordanów, pin Opatowice, pin, eutectoid Opatowice, pin, Sn-rich dendrite composition Opatowice, pin, Sn-poor dendrite composition 16 15 18 17 4 4 2 2 3 5 1 19 20 20 20 Table 5 Cu Sn Sb As Ni Pb S Total 71.38 88.76 24.66 10.13 2.55 0.62 0.65 0.52 0.20 0.12 0.01 0 0 0 99.45 100.15 93.63 5.72 0.11 0.15 0.14 0 0 99.75 96.81 96.79 93.05 86.35 0.95 1.19 5.01 11.41 0.66 0.78 0.72 1.10 0.55 0.67 0.81 0.57 0.13 0.11 0.05 0.03 0.04 0 0 0.03 0 0.01 0 0.01 99.14 99.55 99.64 99.50 92.94 6.49 0.51 0.38 0.06 0.05 0.02 100.45 88.48 9.62 0.79 0.65 0.04 0 0.01 99.59 93.29 6.06 0.59 0.68 0 0.03 0.01 100.66 69.46 65.47 90.74 88.88 74.52 86.99 91.89 24.55 16.90 9.90 10.62 21.91 11.05 6.72 6.06 13.83 0.02 0 2.04 0.80 0.34 0.26 2.33 0 0 0.75 0.51 0.30 0.16 0.07 0.04 0.25 0.06 0.04 0.05 0 0 0 0.01 0 0 0.05 0 0 0.01 0 0 0 0.01 100.49 98.60 100.71 99.76 99.28 99.39 99.36 Representative electron microprobe analyses of the studied Urnfield culture artefacts (wt%) Sample Description 21 22 23 24 7 8 6 6 1Z Szprotawa, grave 2, pin Szprotawa, grave 4, pin 22 Szprotawa, grave 4, pin 23 Szprotawa, grave 4, pendant fragment Żarek, grave 36, pin? Żarek, grave 2, pin Żarek, grave 13, pin? Żarek, grave 13, pin?, inclusion of Cu–Sn Żerniki, grave 18, pin Cu Sn Sb As Ni Pb S Total 91.15 90.57 91.31 92.53 96.35 93.71 87.94 66.10 93.94 5.82 8.08 6.90 6.58 3.18 4.95 12.61 33.32 3.61 0.76 0.12 0.10 0.11 0 0 0.09 0.03 1.03 0.30 0.25 0.37 0.02 0.15 0.29 0 0 0.29 0.95 0.58 0.53 0.11 0.37 0.41 0.05 0.37 0.42 0.11 0.03 0.04 0 0.03 0 0 0.03 0.12 0 0 0.01 0 0 0 0 0 0.01 99.09 99.63 99.26 99.35 100.08 99.36 100.69 99.85 99.42 containing small amounts of Sb and As, and no Ni (Fig. 10). The Sn-enriched composition is also richer in Sb and As (cf., Table 4 and Fig. 10). The metal of the pins contains common small (typically a few micrometres) angular to rounded droplets of Cu–Sn–Sb–As eutectoid (Table 4, analyses 5 and 6) and those of pure Ag, or Bi–Ag, alloy. The ring is made of strongly weathered homogeneous bronze metal containing ∼10 wt% of Sn and practically no Sb, As or Ni (Fig. 7 (e) and Table 4, sample 1). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 16 J. Puziewicz et al. Figure 7 Representative microstructures of the studied ornaments (BSE images). (a) Przecławice: the heavily weathered bead ‘B’ from grave 17 (Únětice stage I). The weathering products (grey, dark grey) surround the metallic core of the bead, which consists of dendrites (sample PZ11 in Table 1). (b) Przecławice: the homogeneous microstructure of the ring from grave 12 (Únětice stage II/III). This kind of microstructure occurs in all Únětice stage III/IV samples (sample PZ4 in Table 1). (c) Przecławice: the directional microstructure of the ring from grave 32 (Únětice stage III/IV), suggesting forging. The elongated black lamellae are voids (sample PZ8 in Table 1). (d) Tomice: an enlarged view of cored dendrites with Sn–Sb rich eutectoid (sample 16 in Table 2). (e) Mierczyce: the deeply weathered, homogeneous bronze ring. The inset shows an enlarged part of the ring, with fine intergrowths of weathering products in the bronze (sample 1 in Table 2). (f) Szprotawa: the weathered pin made of homogeneous bronze (sample 23 in Table 2). © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 17 Bronze Age metal ornaments from Lower Silesia 5 60 50 4 40 Sb Sn 3 30 2 20 stage I, grave 17, bead A stage I, grave 17, bead B stage II/III, grave 12, ring 10 1 0 0 20 30 40 50 60 70 80 90 100 20 30 40 50 Cu 60 70 80 90 100 70 80 90 100 Cu 1.0 4 0.8 3 0.6 Ni As 5 2 0.4 1 0.2 0.0 0 20 30 40 50 60 Cu 70 80 90 100 20 30 40 50 60 Cu Figure 8 Cu versus Sn, Sb, As and Ni variation diagrams (in wt%) for the artefacts from Przecławice, stages I and II/III. The solid symbols are for electron microprobe analyses, and the open ones are for XRF analyses. The composition of the metal forming the dendritic microstructure changes gradually, showing that these are cored dendrites. The changing composition results in a spread of the analytical results: those analyses that yield maximal values for each phase are supposedly the end-members of the cored dendrites. The pin from Jordanów is made of homogeneous metal containing ∼90 wt% of Cu, 10 wt% of Sn, no Sb or As and some (∼0.3 wt%) Ni (Table 4, sample 19). The pin from Opatowice is made of dendritic-microstructure metal with characteristics similar to those of the dendritic metal of the pins from graves 28 and 32 at Tomice (Table 4, analyses 15–17). Urnfield culture, early stages The studied artefacts are made of homogeneous metal, exhibiting granular microstructure upon weathering (Fig. 7 (f)). The ornaments from Szprotawa (three pins and one fragment of pendant) contain ∼6–8 wt% of Sn and 91–92 wt% of Cu plus small (<1 wt% each) amounts of Sb, As, Ni © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 18 J. Puziewicz et al. 5 5 grave 32, ring A grave 32, ring B grave 32, ring C grave 32, ring D grave 33, ring A grave 33, ring B 2 grave 31, ring Sn 3 4 3 Sb 4 2 1 1 0 0 80 85 90 95 100 80 85 Cu 90 95 100 95 100 Cu 5 4 4 3 3 Ni As 5 2 2 1 1 0 0 80 85 90 95 100 80 85 90 Cu Cu Figure 9 Cu versus Sn, Sb, As and Ni variation diagrams (in wt%) for the artefacts from Przecławice, stage III/IV. The solid symbols are for electron microprobe analyses, and the open ones are for XRF analyses. and (the pin from grave 2) Ag (Fig. 12 and Table 5, samples 21–24). Two pins from Żarek contain 3–5 wt% of Sn and 93–96 wt% of Cu, some Ni (∼0.4 wt%) and practically no other elements (Fig. 12 and Table 5, samples 7 and 8). The third one is much richer in Sn (∼12 wt%) and contains 88 wt% of Cu and practically no other elements (Fig. 12 and Table 5, sample 6). It contains small (a few micrometres) inclusions of Sn-rich alloy (Table 5). The pin from Żerniki comes from the late stage of the Urnfield culture. It contains ∼4 wt% of Sn and 94 wt% of Cu, significant Sb (∼1 wt%) and some As, Ni and Pb (Fig. 12 and Table 5, sample 1Z). DISCUSSION The effect of the analytical method The standard analytical approach to the composition of prehistoric metal artefacts comprises the analyses of elements the content of which in individual phases forming the metal exceeds © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 19 Bronze Age metal ornaments from Lower Silesia 5 20 4 15 3 Sn Sb 25 grave 7, ring grave 7, pin no 2 10 2 grave 7, pin no 5 grave 5, pin no 3 grave 10, pin no 4 5 0 1 0 65 70 75 80 85 90 95 100 65 Cu 70 75 80 85 90 95 100 85 90 95 100 Cu 2.0 5 4 1.5 As 3 Ni 1.0 2 0.5 1 0,.0 0 65 70 75 80 85 Cu 90 95 100 65 70 75 80 Cu Figure 10 Cu versus Sn, Sb, As and Ni variation diagrams (in wt%) for the artefacts from Mierczyce, stage III/IV. The solid symbols are for electron microprobe analyses, and the open ones for the XRF analyses. ∼0.1 wt%. It is relatively easy to analyse them by both XRF and the electron microprobe method, or (semi-quantitatively) using EDS systems connected to a electron scanning microscope, and they typically comprise Cu, Sn, S, Pb, As, Sb, Ag, Ni, Co and Fe (e.g., Kienlin 2008). The contents of these elements are shaped by the nature of the ore (oxide versus sulphide) and the content and relative proportions of the metals in it and can help to assess the ore provenance (Pernicka 1999). The lead isotopes are also commonly used to indicate the possible ore source (Gale and Stos-Gale 1982; see also, e.g., Ling et al. 2014). Other elements are rarely analysed; for example, besides the listed elements and lead isotopes, Cooper et al. (2008) also analysed Cr, Se, Cd and Au, which have been used to show the potential provenance of artefacts produced from native copper in the northern part of North America. The XRF method applied by us is expected to yield reasonable results for homogeneous metals, where the size of the analysed spot is of little importance (cf., for example, the XRF and © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 20 J. Puziewicz et al. 5 20 4 15 3 Sb Sn 25 10 2 5 1 0 0 65 70 75 80 85 90 95 100 65 70 75 80 Cu 85 90 95 100 Cu 5 2,0 Tomice, grave 34, pin Tomice, grave 28, pin 4 1,5 Tomice, grave 31, ring Tomice, grave 22, pin As 3 Tomice, grave 21, bracelet Jordanów, grave 163, pin Opatowice, pin Ni 1,0 2 0,5 1 0 0,0 65 70 75 80 85 90 95 Cu 100 65 70 75 80 85 90 95 100 Cu Figure 11 Cu versus Sn, Sb, As and Ni variation diagrams (in wt%) for the artefacts from Tomice, Jordanów and Opatowice, stage III/IV. The solid symbols are for electron microprobe analyses, and the empty ones are for XRF analyses. microprobe data for homogeneous items from Tomice, Fig. 11: the ring from grave 31, the pin from grave 22 and the bracelet from grave 21). However, the ring from grave 7 at Mierczyce exhibits a significant spread of XRF data relative to the microprobe results (cf., Fig. 10), despite being made of homogeneous metal. The ring is, however, strongly weathered (cf., Fig. 7 (e)) and in our opinion the XRF analyses are affected by small intergrowths of decomposition products. This example shows that the XRF method alone may yield spurious results even if the analysed artefacts are composed of homogeneous metal. The XRF analyses of polyphase metal show ‘average’ compositions, whereas those made using the electron microprobe yield information on the composition of single phases. Commonly, the XRF analyses show an element content that is intermediate between the extremes defined by the electron microprobe—compare, for example, the pins from Mierczyce, which are all dendritic (Fig. 10), or the dendritic pins from graves 28 and 34 in Tomice (Fig. 11). This effect is disturbed © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 21 Figure 12 Cu versus Sn, Sb, As and Ni variation diagrams (in wt%) for the artefacts from Urnfield sites, stage III/IV. The solid symbols are for electron microprobe analyses, and the empty ones are for XRF analyses. when the metal is deeply weathered and contains decomposition products, such as in the case of the beads from grave 17 in Przecławice (cf., Fig. 8). The chemical variation of ornaments The Únětice culture stage I and II/III ornaments from Przecławice are made of bronze and thus contain significant amounts of tin, whereas the artefacts from stage III/IV graves were produced from copper devoid of tin. The Únětice culture classical stage ornaments from neighbouring sites (Mierczyce, Tomice and Opatowice) are made of bronzes, except for the pin from grave 22 in Tomice, which is compositionally similar to the stage III/IV copper ornaments from Przecławice. Thus, the oldest Únětice culture ornaments in the studied set were made of bronze, stage III/IV is marked by the copper ornaments from Przecławice, and the younger ‘classical’ stage of the Únětice culture is characterized by bronze metal ornaments. Bronze is also used for the Urnfield © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• 22 J. Puziewicz et al. culture products from Szprotawa, Żarek and Wrocław-Żerniki. The Únětice culture bronzes are typically dendritic and consist of cored dendrites plus Sn–Sb-rich eutectoid; they contain significant amounts of Sb and As and little Ni. The Urnfield culture bronzes are homogeneous, and contain little Sb and As and significant amounts of Ni (cf., Figs 8 and 10–12). This reveals the technological improvements, leading to the production of homogeneous metal. The flat distribution of points in the Cu/Sb and Cu/As diagrams that show the composition of the Urnfield culture ornaments suggests that the metal was multiply recycled or deliberately oxidized during smelting, which lowered the Sb and As contents, which are volatile in the form of oxides during smelting. The As and Sb contents suggest that the studied ornaments of the Únětice culture have been produced from fahlore, which is a mixture of the metal sulphides with the prevailing tetrahedrite (ideally (Cu,Fe)12Sb4S13) – tennanite (ideally (Cu,Fe)12As4S13; for details of possible chemical composition variation, see Krismer et al. 2011) solid solution. The major element composition of the copper Przecławice ornaments makes them similar to the East Alpine Copper, produced from fahlore with Ni [Przecławice compositional types (1), (2) and (4)] or to Ösenring copper, produced from fahlore without Ni [compositional types (3) and (5)] (Krause 2003). The occurrences of tin in Europe are much less numerous than those of copper. The area of Lower Silesia is located between the Erzgebirge tin deposits to the west and the Slovakian (West Carpathians) deposits to the east. The Erzgebirge deposits are closer but, instead, the Slovakian deposits are considered to be the source of the tin used in the Bronze Age in Central Europe (Krause 2003 and references therein). Archaeological comments Silesia is considered to be the area that, compared to other parts of Poland, has provided the greatest amount of archaeological evidence on early copper and bronze metallurgy. Although evidence of local production is rather scarce, the distribution of local types of certain artefacts indirectly indicates its beginnings in the late stages of the Únětice culture (e.g., Gediga 1982, 110). Urnfield period sites have produced abundant data on stable and advanced local metalworking, with hundreds of casting moulds, semi-finished and completed products and workshop remains (Gediga 1982, 111–28). The early Bronze Age ornaments have rarely been the subject of detailed material studies, which have focused rather more on later, massive artefacts such as axes or necklaces. Small simple beads and rings made of wire or sheet are the most common type of early Bronze Age metal products in south-western Poland prior to the classical (V) stage of the Únětice culture, when pins become more frequent (Butent-Stefaniak 1997, 234; Kadrow 2001, 92). The compositions of ornaments varies broadly and shows no well-defined time-composition trend (Sarnowska 1975, 97–9), as opposed to the composition of axes from several early Bronze Age Polish sites, which shows gradual change from older low-Sn alloys to the younger, Sn-richer ones (Sarnowska 1975, 101; Rassmann 2004). However, a simple axe-based model of evolving metal composition is commonly, although not generally, accepted (Kienlin 2010, 168, 171–2 and references therein). The Przecławice ornaments do not fit this model (early stages, Cu–Sn alloys; later stages, Cu alloys). This may be due to completely different properties sought by early metalworkers and, in consequence, different working strategies. In the case of tools, the hardness (obtained both by control of temperature and cold working; e.g., Kienlin 2007, 8) was the most desired property, while for ornaments it could have been of little interest, and colour or ductility were of greater importance (Kienlin 2010, 171). Unlike at Przecławice, the bronze ornaments © 2014 University of Oxford, Archaeometry ••, •• (2014) ••–•• Bronze Age metal ornaments from Lower Silesia 23 dated to the classical stage of the Únětice culture from the other sites represent an advanced level of metalworking skills and probably the same strategies both in ornament and tool production. Data obtained from the ornaments dated to the Urnfield period prove that this model had been continued from the late early Bronze Age onwards. CONCLUSIONS Our data show that the best choice for the characterization of metal artefacts is the combination of methods yielding averaged chemical compositions with methods enabling micrometre-scale imaging of the metal microstructure, plus chemical analyses. These methods allow reasonable characterization of metal items that consist of dendrites or are polyphase, as well as of those that are weathered or corroded and contain micrometre-scale decomposition products dispersed in the host. We used XRF analyses plus electron microprobe BSE imaging and spot analyses, but other choices of analytical equipment can provide similar information (e.g., a scanning electron microscope equipped with an EDS module can be used instead of the electron microprobe). The ornaments coming from Únětice culture sites in Lower Silesia are made of bronzes of varying Cu/Sn ratios. The chemical variation of their composition and their typically dendritic metal microstructure suggests rather poor control of the smelting and solidification process. The exception is the Przecławice site. The metal composition evolution in Przecławice ornaments (from bronze of the older Únětice culture to copper of the young stage) is the opposite of that accepted on the basis of axe composition studies, probably due to different working strategies used to produce tools/weapons and ornaments. 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