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Archaeometric studies on early medieval silver jewellery from Central and Eastern Europe

Archaeometric studies on early medieval silver jewellery from Central and Eastern Europe Scanning electron microscopy with X-ray microanalyses (SEM-EDX) was used for a technological study of silver jewellery from three hoards found in Poland. The assemblage consists of 26 artefacts from the period of formation of the first Polish state (900– 1039 AD) and can be divided into three groups: West Slavic, post-Moravian and Scandinavian. Research results provide information concerning techniques used for granulation ornament and the provenance of raw silver. Elemental composition changes are manifested mainly by different Cu contents. A higher Cu content was found in solder. The higher Cu content in relation to the morphology of the joining region with visibly spilled granulation demonstrates that the West Slavic beads were produced with the use of metallic soldering. On the other hand, other studied jewelleries are characterised by Cu, Sn, Sb and Zn enrichments in oxidised soldering regions, which implies that they were manufactured with the use of non-metallic soldering. In addition, studies on the provenance of the raw material were made based on the analysis of lead isotopic ratios. For this purpose, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used, and the obtained lead isotopic ratios were processed using linear discriminant analysis (LDA). The isotope study demonstrates that all examined artefacts were made using re-melted metal from multiple sources. The most probable sources of silver were ores from Uzbekistan, Afghanistan and Freiberg (Germany). . . . . Keywords SEM-EDX LA-ICP-MS Lead isotope ratios Medieval jewellery Silver hoards Introduction Poland (Dekówna 1974; Zoll-Adamikowa et al. 1999). Assemblages consisting of coins and other kinds of silver arte- The aim of this paper is to discuss the results of recent research facts are important historical source materials from which it is conducted on female ornaments from early medieval hoards in possible to obtain data about economic, political and social conditions of people who were depositing silver. These issues are crucial for understanding the relations between early states Electronic supplementary material The online version of this article in Central Europe, mainly between the first Polish state created (https://doi.org/10.1007/s12520-019-00935-z) contains supplementary by the Piast Dynasty, the Czech state and Scandinavian coun- material, which is available to authorized users. tries. The custom of deposition of silver and gold artefacts in the form of hoards was of Scandinavian origin and went into use in * Ewelina Miśta-Jakubowska Ewelina.Mista@ncbj.gov.pl Piast Poland, but not in the Czech lands ruled by the Přemyslid Dynasty. The hoards, consisting of coins and ornaments, usu- 1 ally hacked into pieces, appear in the realm of the Piasts for the National Centre for Nuclear Research, A. Sołtana 7, first time in the mid-tenth century, and their number gradually 05-400 Otwock, Poland 2 increases until the custom of hoard deposition disappears in the Institute of Archaeology and Ethnology, Polish Academy of beginnings of the twelfth century (Jakimowicz 1933; Sciences, Al. Solidarności 105, 00-140 Warsaw, Poland Kostrzewski 1962). The ornaments from these hoards are cov- Institute of Nuclear Chemistry and Technology, Dorodna 16, ered with granulation, which was a decoration with ancient 03-195 Warsaw, Poland traditions (see, e.g. Duczko 1985 Eilbracht 1999; Pliny 1929; Institute of History, Jan Długosz University in Częstochowa, Al. Theophilus 1979; Ogden 1982). Granulation was a favourite Armii Krajowej 36a, 42-200 Częstochowa, Poland 6706 Archaeol Anthropol Sci (2019) 11:6705–6723 ornamentation technique among craftsmen working for social 1980s (research on finds from Birka in Sweden) and did not elites in the first state of the West Slavs, that is, Great Moravia, contain detailed analyses of physico-chemical traits of in the ninth century AD. The origins of ornaments are to be discussed finds (Duczko 1972, 1984, 1985, 1986). This issue, searched in the traditions of Late Roman Art which survived in on a larger scale, is currently being researched by the authors the Byzantine Empire. Moravian ornaments, which are known as part of two grants in collaboration with the University of only from burials, are of very high quality and represent a Stockholm and the National Museum in Stockholm. special phenomenon in early medieval European art (Čáp et al. 2011;Galuška 2013). After the destruction of the Moravian state inthe earlytenthcenturybythe Hungarians, Material and methods Moravian goldsmiths moved in two directions: westward to the Czech state, and eastward to Kievan Rus, created and ruled by Archaeological material the Scandinavians. Each group of these craftsmen created their own repertoire of types characteristic only for them. In the This paper discusses the results of research on 26 ornaments hoards found in the territory of the Piasts, there is a prevalence from three early medieval silver hoards discovered in of ornaments typical for the Czech art, while ornaments of the Słuszków, Rajsków and Stojkowo in Poland (see Fig. 1). eastern group are known from hoards deposited by the Rus, i.e. The hoard from Słuszków (Kalisz District, Poland) is one of the Scandinavians living in Eastern Europe (Ukraine, Belarus the largest ones of such kind in Poland (see Fig. 2). It was and the European part of the Russian Federation). In the eastern discovered in 1935 during land adjustment. Today, the hoard hoards, post-Great Moravian ornaments were mixed with typ- is in the collection of the District Museum of the Kalisz Region. ical Norse jewellery, in which the techniques of filigree and The assemblage contains 13,061 finds, most of which being granulation were also employed. Post-Great Moravian orna- cross denars. The latest issues come from the end of the elev- ments hold a special place in the European history of art, be- enth and the beginning of the twelfth century. The most numer- cause of their own unique nature. As all jewellery, also those ous group in the hoard consists of cross denars of types I, II, IV, had religious and social functions (Duczko 2015, 2016, 2018). V, VI, VII and VIII. It includes 12,829 items, which is over 98% A few experimental technological studies were done of artefacts in the assemblage. In addition, the Słuszków hoard (Thouvenin 1971, 1973;Baines 2005) however, they did not also contains 32 granulated silver beads decorated with filigree cover physico-chemical properties of jewellery of such type. (25 items with bosses, 4 oval ones and 3 small fragments of Published results of contemporary studies on ornaments made silver sheet with traces of granulation), 7 silver ingots and 71 with the use of granulation and filigree techniques are mainly foreign coins: Arabic, English, Danish, German, Czech and focused on gold artefacts (e.g. Scrivano et al. 2013, 2017a, b; Hungarian, mostly preserved in fragments. However, the most Ontalba Salamanca et al. 1998; Šmit et al. 2000, Šmit and spectacular group in the hoard are Palatine Sieciech’s denars: Šemrov 2006). 120 items with a cross pattée and 1 + 2 with a monogram. It is A recent study by Ashkenazi et al. (2017, 2018)concerns the largest known assemblage of coins of this magnate. results of research on silver treasures whose chronology The second of the examined hoards was accidentally dis- strongly precedes the finds discussed in this article. In recent covered in 1992, when a residential building in the Kalisz- years, Czech researchers have commenced to fill this gap. Rajsków quarter was extended (see Fig. 3). Part of the hoard What can be mentioned here is a series of archaeological ex- is kept in the Kalisz Museum and it includes 636 finds with a periments on the technology of manufacture of early medieval total weight of 281.2 g. In this part of the hoard, 146 entirely ornaments from Great Moravia, with a special focus on fili- preserved oriental coins and their fragments (a fragment of an gree and granulation (Čáp et al. 2011). Another important Arab-Sasanian drachma from the end of the seventh century, work deals with the composition of metal, construction and and dirhams dated to the period between the end of the sev- technology of goldsmith decorations discovered at the enth and the end of the tenth century) were distinguished. BLumbe Garden^ cemetery at Prague Castle (Ottenwelter Furthermore, German denars and their fragments, including et al. 2014). Ornament analyses were carried out by scanning the earliest type I cross denars, Czech and Scandinavian coins, electron microscopy using X-ray dispersion spectrometry. Yet as well as issues of Bolesław Chrobry (type CNP 47) from the another valuable study is a monograph with a detailed discus- initial period of this ruler’s reign were present in the assem- sion on finds from Břeclav - Pohansko VII, including scan- blage. There are 490 fragments of ornaments in the hoard, of ning electron microscopy of Great Moravian jewellery from which 16 specimens were selected for archaeometric research. the Pohansko site (Macháček et al. 2016). The third early medieval silver hoard discussed in this pa- However, the early appearance of Czech ornaments in per was discovered in 1926 in a village of Stojkowo (Fig. 4), Europe did not attract enough attention from researchers. W. 10 km to the east of Kołobrzeg (Kolberg) and is deposited Duczko studied Danish Viking ornaments, including Slavic now in the National Museum in Warsaw. Only a part of it weighting about 740 g has survived, while the rest weighting artefacts. His first works were published in the 1970s and Archaeol Anthropol Sci (2019) 11:6705–6723 6707 Fig. 1 Map of finds of the silver hoards discussed in this paper about 400 g and a covered clay vessel in which the hoard far from adequate and precise (Kiersnowska and was buried were lost during the Second World War. The Kiersnowski 1955). preserved part consists of 102 coins (chiefly from German mints and 28 cross denars of types I, II, III, V, VI and Structural and elemental composition analyses VII), 9 lumps of cast silver or their fragments, 39 frag- ments of silver bars and silver sheets, 159 fragments of Before laboratory analyses, the artefacts were cleaned in silver sticks and wire and 152 various silver ornaments AVEL Silver Cleaner solution (http://www.avel.com/avel-33/ (parts of rings, temple-ring pendants, silver beads, chains, produit/293-silverware-avel-33.html, accessed on 2 August necklaces and buckles), mostly hacked and broken. 2017), and then they were bathed in acetone and air dried in Probably about 400 coins (mostly dirhams) and some oth- order to remove conservation layers. The conservation of the er artefacts, among them a few fragments of silver bars, jewelleries included mechanical cleaning, application of 5% were lost. Information concerning this lost part of the disodium edetate solution (Ślesiński 1995) and covering the hoard was obtained from literature. However, this data is surface with Paraloid B-72 acrylic resin (Costa 2001). The 6708 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 2 Silver beads from the early medieval hoard from Słuszków: West Slavic group. Photo: M. Osiadacz state of preservation of the finds was good and no corrosion The SEM-EDX study provided information about morpho- was observed. logical changes and allowed for a determination of the quan- SEM-EDX (scanning electron microscopy with X-ray mi- titative elemental composition in the micro-scale, taking spec- croanalysis) was the main technique which was used for the ifications of the solder region, base surface and granule com- study of technological changes in surfaces of the discussed positions into account. The granules and surface where they ornaments. This was due to the surface interaction of the ex- were attached by soldering are referred to as the base surface citation electron beam and a possibility of EDX signal regis- in the further part of this paper. This was due to their similar tration from near-surface layers (Gójska et al. 2019) in the elemental composition. For each technological area of a given region of soldering occurring up to about 30 μm from the artefact, at least n = 3 measurements were carried out. The surface (Kolářová et al. 2014). SEM-EDX analysis, described SEM-EDX analysis was done using a Carl Zeiss EVO in detail in Goldstein et al. (2007), is a popular non-destructive MA10 Scanning Electron Microscope equipped with an technique used in studies of archaeological finds (e.g. EDAX X-Flash Detector 5010 with a 123-eV spectra resolu- Scrivano et al. 2017a, b; Ontalba Salamanca et al. 1998; tion (Zeiss. Poland; www.zeiss.com) and provided with a Ashkenazi et al. 2017, 2018; Linke and Schreiner 2000, Bruker Quantax 200 Esprit 1.9 system for analyses of EDX Linke et al. 2003, 2004;Ingo etal. 2004;Miśta et al. 2017; spectra. The image analysis was carried out using a secondary Gójska and Miśta 2016). Twenty-six artefacts were tested electron detector (SE) with a resolution up to 2.0 nm. Other altogether. parameters were the following: accelerating voltage 20 keV, Fig. 3 Silver ornaments from the early medieval hoard from Rajsków: a post-Moravian group; b West Slavic group; c Scandinavian group. Photo: M. Osiadacz Archaeol Anthropol Sci (2019) 11:6705–6723 6709 Fig. 4 Silver ornaments from the early medieval hoard from Stojkowo: Scandinavian group. Photo: M. Osiadacz measurement time 120 s and LLD = 0.1 wt%. The current and density estimator (KDE) model was used to obtain a 3D mod- field magnification was adjusted to the type of morphology of el of lead isotopic ratio distribution in artefacts (Kulczycki each studied surface. The quantitative analysis was done using 2005; Baxter 2003, 2016; Everitt and Hothorn 2011;Everitt the non-pattern method with an error < 3% for the main ele- et al. 2011). ments and < 20% for traces below 1 wt%. Standard reference materials which were used for EDX result authentication were Ag and Cu alloy mixtures in all Ag/Cu % range (ESPI metals). Results Lead isotope analyses SEM-EDX analysis of technological changes Furthermore, an ore provenance study was carried out based in the surface of the ornaments on the results obtained for 20 ornaments. The micro-invasive LA-ICP-MS was carried out with an ELAN 9000 Inductively A series of 26 silver ornaments—18 made in filigree and Coupled Plasma Mass Spectrometer (Perkin Elmer SCIEX, granulation techniques (in one find from the Rajsków Canada: www.perkinelmer.com) equipped with an LSX- hoard—the artefact without no. in Fig. 3—the soldering area 200 laser ablation system (CETAX, USA: www.cetax. was not identified by the SEM-EDX analysis) and 8 without com). The LSX-200 combines a stable environmentally such decoration (the finds from the Stojkowo hoards, see in selected 266-nm UV laser (Nd-YAG, solid state, Q-switches) Fig. 4)—were examined. These artefacts belong to the West with a high sampling efficiency, variable 1 to 20 Hz pulse Slavic (12 finds—5from Słuszków, see Fig. 3,and7from repetition rate and maximum energy up to 6 mJ/pulse. The Rajsków, see in Fig. 3b), post-Moravian (4 finds from applicability of this technique in archaeological provenance Rajsków, see Fig. 3a) and Scandinavian (10 finds—2from analyses is briefly discussed by several authors (e.g. Baker Rajsków, see Fig. 3c, and 8 from Stojkowo, see Fig. 4)groups. et al. 2006;Budd etal. 1995;Hirata 1996; Stos-Gale & Gale The technological groups were isolated based on visual char- 2009). The NIST 981 reference standard material was used for acterisation according to Duczko (1985). quantitative determination of lead isotope concentrations (0. The surface morphology of all precious metal artefacts was 204/206 207/206 059042, 0.91464 and 2.1681 for Pb ,Pb and studied by SEM-SE. In the case of ornaments with granula- 208/206 Pb with relative standard deviation below 0.1%). tion, three technological areas were identified: 1—base sur- Measured median values (n = 78) with relative standard devi- face made of silver alloy; 2—joining zone located between the ation are 0.0610 ± 1.08, 0.0915 ± 1.02 and 2.1720 ± 1.16% for surface and the decoration; and 3—ornamentation on the base 204/206 207/206 208/206 Pb ,Pb and Pb , respectively. For each arte- silver alloy, e.g. granulation and twisted wire. fact, n = 40 measurements were carried out with SD: < 6% for Furthermore, on the basis of morphological differences in 206 207 208 206 207/204 Pb /Pb , < 7% for Pb /Pb and < 5% for Pb . the ornamentation zone which were identified by SEM obser- The obtained results of the elemental composition and lead vations, three types of joining were found: (i) spilled granula- isotope study were processed using principal component anal- tion ornaments, (ii) non-oxidised spherical granules and (iii) yses (PCA) and linear discriminant analysis (LDA). A kernel oxidised soldering area with spherical granules. 6710 Archaeol Anthropol Sci (2019) 11:6705–6723 All the analysed beads from Słuszków display similar char- Stojkowo hoard resemble Scandinavian-type artefacts without acteristics of the soldering area with the lack of extensive granulation (see Fig. 4). oxidised structure in the soldering region. Such structures as- What is important while analysing the results is that the sociated with two different solder types are presented in elemental composition determined for each technological part Figs. 5 and 6. Figure 5 (surface of find 2 from Fig. 2)offers is only approximate due to a considerable blur of the elements’ examples of SEM-SE images recorded for the first type of the distribution on the surface micro-regions. This results from the joining structure. This variety is characterised by granules fact that these ornaments were processed at high temperatures which are smoothly embedded in the surface. The size of these (Untracht 1985; Wolters 1983). In our study, the division into granules is about 300 μm (see Fig. 5). Moreover, the shape of the base surface and the soldering area was confirmed by the the granules is fuzzy and a significant merging with the solder linear discriminant analysis. Table 2 presents the results of structure can be seen. The ornament is spilled on the surface. LDA correct allocation for two selected (based on elemental Furthermore, in Fig. 6, one can see granules separated from composition in Table 1) technological areas. The greatest spill the solder layer which is characterised by the lack of extensive of solder over the surface is visible in the WSS type. Based on oxide structures. The size of these granules is about 400 μm the results presented in Table 2, the division shown in Table 1 (see Fig. 6). seems to be appropriate. Different technological types of joining areas were ob- As it can be seen in Table 1, the soldering area of the West served in the case of ornaments from the Rajsków hoard. Slavic artefacts from Rajsków is the most oxidised (O up to Figures 7 and 8 offer SEM-SE images of a micro-region with 51.4 wt%) with the highest concentration of copper (Cu) up to the granulation ornament. Cloudy shapes of joining structures 57.3 wt% and high tin (Sn) and antimony (Sb) contents. The between granules are visible with the size of the granules from solder in the post-Moravian jewelleries (see Figs. 7 and 8)is 300 (see Fig. 8)to 400 μm (see Fig. 7). similar with regard to the content of O, while it has a lower Cu Based on the SEM images, it can be said that the spilled content (up to 27.8%) and slightly higher Sn (up to 24.7 wt%), ornament (as discussed below) with relatively small size of the Pb (up to 7.0 wt%) and Sb (up to 19.5 wt%) concentrations. granules and the lack of oxide structures indicates the use of Concerning the solder type, all five beads from Słuszków metallic soldering (Ottenwelter et al. 2014;Macháček et al. are characterised by the lack of very oxidised structure (see 2016; Ferro et al. 2009) in the case of the beads from the Figs. 5 and 6) with the O content in the range from 3.3 to Słuszków hoard. The presence of oxide structure in the area 22.6 wt%. The Cu, Sn and Zn contents are also low, as com- of tiny granule assemblage in the finds from Rajsków could be pared with other types of jewelleries (see Table 1)withslight a chemical soldering effect (Čáp et al. 2011;Duczko 1985). Pb and Cu enrichment. The elemental composition study results confirm the above The soldering area of the Scandinavian jewelleries from assumption, as described below. Rajsków is enriched in Cu, Sn, Sb, Pb and O with regard to Furthermore, the EDX elemental composition of orna- their base surface. The base surface of the finds without gran- ments allowed to distinguish technological micro-areas within ulation from the Stojkowo hoard is different from other types three archaeological types. Ag, Cu, Bi, Pb, Zn, Sn, Au, Hg, Sb of the base surface (see Fig. 9a). It is enriched in Cu and Pb. and O concentrations above 0.1 wt% were identified as a Generally, the elemental composition differences determined normalised value. The results are presented in Table 1.The for all the types of jewelleries are presented graphically below, West Slavic and Scandinavian types were divided into two both as a difference in the content of elements in the soldering groups according to visual traits, i.e. beads from Słuszków areas (see Fig. 9b) and raw silver (see Fig. 9a)which was usedto have a different soldering area as shown by SEM analyses produce the base surface and ornaments. In the diagrams below, (see Figs. 5 and 6). On the other hand, the finds from the all EDX measurements were taken into account. Fig. 5 SEM-SE images of the surface of the silver bead from Słuszków (Fig. 2: no. 2) characterised by spilled granulation ornament. The technological parts are as follows: 1—base surface, 2—soldering area and 3—granules as part of the granulation ornament Archaeol Anthropol Sci (2019) 11:6705–6723 6711 Fig. 6 SEM-SE images of the surface of the silver bead from the Słuszków hoard (Fig. 2: no. 3), find 12683. Regular spherical granules without extensive oxidised solder area can be seen. Designations (1–3) as in Fig. 5 Figure 9 shows the results of the elemental composition accordance with what is offered in Table 2). The main classi- analysis presented as a LDA diagram (Baxter 2016, 2003; fication error occurs only in Fig. 15: point II. In all PCA Everitt and Hothorn 2011). The LDA confusion matrix can diagrams, the Ag content is correlated with the base surface, be found in Table 3. while Cu, Sn, Zn, Sb and Bi are related to the soldering region. As it can be seen in Fig. 9 and Table 3, the base surface However, as reported by Kolářová et al. (2014), the registered regions in all types of jewelleries with granulations are similar EDX signal gives information about the base surface contam- concerning their elemental composition. A better separation inated by solder components (Wolters 1983). (61%) is observed for the artefacts without granulations from In Fig. 10, in the soldering area, there are two notable the Stojkowo hoard. Furthermore, in the case of the soldering anomalies with higher Cu (up to 29.5 wt%), Sn (up to area, a better allocation to the group can be seen for WSS 8.8 wt%), Sb (up to 4.6 wt%) and O (up to 56.5 wt%) contents. (72%), WSR (54%) and Sc.R (50%). The soldering regions They concern find no. 2 in Fig. 3c. The SEM-SE images of the of PM jewelleries are similar to all other types and the alloca- soldering region of this pendant can be seen in Fig. 11.In turn, tion to the predicted group is 30%. Figures 10, 12, 14 and 15 the composition of this joining area is slightly similar to what illustrate a graphical distribution of variability of Ag, Cu, Bi, occurs in the WSR and PM type (see Fig. 9b). Au, Pb, Hg, Sn, Zn, Sb and O concentrations. In the diagrams, The largest anomalies within the soldering area are present there are marked areas (respectively, I–II, a–c) with composi- in the PM group, which is also evidenced by the LDA results tion anomaly in the groups in question. Figures 10b, 12b, 14b presented in Table 3 (only 30% of correct allocations). There and 15b (as a fragment of Fig. 9b) present LDA separation of are observed anomalies in the concentration of low-melted the soldering area for each artefact within archaeological elements such Pb, Sn, Zn, Sb, Bi and Cu. These anomalies groups. Numerical designations of the finds are explained in can be seen in the case of finds nos. 2 (no a, b, I in Fig. 12)and Figs. 2 and 3. Moreover, the a) parts of Figs. 10, 12, 14 and 15 4 (no c, II, III in Fig. 12)fromFig. 3a.The firstone is contain PCA correlation-type diagrams presenting the results characterised by a much higher content of Sb (up to of the elemental composition analyses of the soldering region 19.5 wt%), Sn (up to 24. 7 wt%) and Cu (up to 27.8 wt%) and the base surface in each technological group. with higher Pb, Zn and O concentrations. The other one is Generally, as it is shown in the PCA diagrams from panels characterised by the oxidised soldering region (up to a of Figs. 10, 12, 14 and 15, the division into the base surface 50.4 wt%) with higher Cu and Sn concentrations, as it can and the soldering region within a given archaeological group be seen in Fig. 7. In the PCA diagram (Fig. 12a), there are based on the elemental composition is justified (which is in strong Sn–Sb and Zn–Cu correlations, which means that these Fig. 7 SEM-SE images of the surface of the silver bead from the Rajsków hoard (see Fig. 2: no. 4). An oxidised solder area and regular spherical granules can be seen. Designations (1–3) as in Fig. 5 6712 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 8 SEM-SE images of the granulation area of the silver bead surface from the Rajsków hoard (see Fig. 2: no. 1). There are oxidised soldering structures (2) located in the space between granules (3) components could be added in this substrate correlation to the earring with filigree (Fig. 3b: no. 6, WS type); an earring (PM joining mixture. Figure 13 shows the soldering region of the type); a round pendant (Sc type); and a raspberry pendant (PM abovementioned pendant marked as no. 2 in Fig. 3a. type)—a slightly increased content of gold and mercury was The raspberry pendant presented below is an example of an detected in the micro-region. ornament characterised by higher contents of low-melted ele- The soldering region of the WSR group is characterised by ments in the oxidised solder areas. Moreover, a higher per- 54% allocation to the correct group with a high (31%) alloca- centage of gold (Au) up to 2.7 wt% and mercury (Hg) up to tion to the PM group (see Table 3). The two anomalies are 2.4 wt% was recorded in the entire artefact. Generally, for the observed for two artefacts: nos. 2 (see point I in Fig. 14)and 3 entire assemblage from the Rajsków hoard, the mercury en- (see point a in Fig. 14)fromFig. 3b. Generally, the entire richment (up to 4.0 wt%) is mainly observed for the base soldering area of the WSR group is oxidised and characterised surface, but in some cases, it is also related to the soldering by the positively correlated Sn, Cu and Sb contents, while in region. For five ornament fragments—a bead with a bump, the PM group there is the oxidised soldering area with corre- WS type (see Fig. 3b: no. 2, see Fig. 14 below point I); a starry lated Cu–Zn and Sb–Sn contents (see Fig. 12). Moreover, the Table 1 SEM-EDX analysis results Arch. type Hoard Tech. area (wt%) Ag Cu Bi Au Pb Hg Sn Zn Sb O West Slavic Słuszków (WSS), Base surface Av. (n = 37) 87.8 3.4 0.7 0.7 0.7 0.7 0.1 0.1 < 0.1 6.0 5obj. Δ 72.6–95.6 < 9.5 <3.4 < 4.7 <3.4 <3.1 <1.1 <1.0 < 0.1 1.2–16.0 Soldering area Av. (n = 21) 79.5 6.7 1.3 0.9 1.7 0.9 0.3 0.2 0.1 8.5 Δ 63.1–88.7 2.4–11.0 <5.0 < 4.2 <6.3 <2.8 <1.7 <0.9 < 0.9 3.3–22.6 Rajsków (WSR), Base surface Av. (n = 42) 88.8 3.9 0.4 0.6 0.5 0.5 0.3 < 0.1 < 0.1 4.8 7obj. Δ 69.3–95.7 2.3–9.4 < 3.0 < 3.4 < 3.5 < 2.8 < 2.1 < 0.1 < 0.1 < 20.7 Soldering area Av. (n = 26) 33.4 23.0 1.0 0.7 1.0 0.6 3.9 0.5 2.2 33.7 Δ 2.2–87.6 3.4–57.3 < 9.5 < 6.2 < 6.6 < 3.8 < 18.6 < 2.3 < 13.1 4.3–51.4 Post-Moravian Rajsków, (PM), Base surface Av. (n = 41) 87.9 3.2 0.9 1.0 0.3 1.1 0.1 0.1 < 0.1 5.6 4obj. Δ 75.8–99.0 0.5–6.0 < 4.0 < 3.2 < 2.8 < 4.0 < 1.4 < 0.7 < 0.1 < 18.4 Soldering area Av. (n = 30) 50.6 12.7 1.1 1.2 1.7 0.9 4.9 0.5 2.3 24.2 Δ 4.9–75.7 4.4–27.8 < 5.4 < 3.1 < 7.0 < 3.4 < 24.7 < 2.3 < 19.5 9.3–50.4 Scandinavian Rajsków Base surface Av. (n = 8) 90.2 3.2 0.2 0.6 0.3 1.1 0.2 0.1 < 0.1 4.2 (Sc. R), 2 obj. Δ 83.4–96.3 1.4–6.1 < 1.5 < 3.4 < 1.6 < 2.2 < 0.7 < 0.6 < 0.1 1.4–7.7 Soldering area Av. (n = 9) 58.3 11.8 0.6 1.5 1.6 1.2 2.8 0.2 1.1 20.9 Δ 5.0–80.1 4.6–29.5 <3.5 < 4.9 <4.8 <2.7 <8.8 <1.1 < 4.6 8.3–56.5 Stojkowo Base surface Av. (n = 31) 84.9 6.0 1.2 0.8 1.4 0.7 < 0.1 0.4 < 0.1 4.6 (Sc. St), 7 obj. Δ 60.6–92.2 2.8–17.3 <3.1 < 2.3 <3.5 <2.7 <0.6 <1.3 < 0.1 0.7–21.2 n number of measurements, Δ range of composition variation for the technological area Archaeol Anthropol Sci (2019) 11:6705–6723 6713 Table 2 Part of the LDA confusion matrix for the training sample Table 3 LDA confusion matrix for the training sample. Data obtained showing correct allocation for the technological areas of the for the base surface and the soldering area of jewelleries groups archaeological types (two training sets/technological group—base sur- From/to Sc.R Sc.St PM WSS WSR face and soldering area; 10 variables: Ag, Cu, Bi, Au, Pb, Hg, Sn, Zn, n (%) Sb, O) Correct allocation: n (%) Base surface Soldering area Base surface (as in Fig. 9a) Sc.R 2 (25%) 2 (25%) 2 (25%) 0 (0%) 2 (25%) Sc.R 6 (75%) 10 (100%) Sc.St 2 (7%) 19 (61%) 3 (10%) 2 (6%) 5 (16%) PM 41 (100%) 25 (83%) PM 10 (24%) 0 (0%) 13 (32%) 10 (25%) 8 (19%) WSS 28 (80%) 14 (67%) WSS 2 (6%) 5 (14%) 8 (22%) 12 (33%) 9 (25%) WSR 42(100%) 22(85%) WSR 10 (24%) 5 (12%) 5 (12%) 9 (21%) 13 (31%) Soldering area (as in Fig. 9b) Sc.R 5 (50%) – 0 (0%) 3 (30%) 2 (20%) WSS soldering region demonstrates a better Pb–Zn PM 7 (23%) – 9(30%) 6(20%) 8(27%) correlation. WSS 3 (14%) – 2 (9%) 15 (72%) 1 (5%) The soldering region of the WSS group is in 71% of cases WSR 1 (4%) – 8 (31%) 3 (11%) 13 (54%) allocated to the correct group. Only six measurement points are better assigned to other groups (see Table 3). This group is n number of measurements best distinguished in terms of the solder composition (see Fig. 9b). However, the distinction between base and soldering is is important to know whether the silver comes from one or the most disturbed (as shown in Table 2 and Fig. 15a), which many different sources. It may be supposed that re-melting of is an effect of spilling of the solder over the surface (Wolters earlier artefacts took place in Europe since the Migration 1983). In Fig. 15, there are four protruding points in the group Period (400–800 AD). Therefore, one can expect more than with different compositions. These compositions are related to one value of individual isotopic ratios in one and the same two artefacts. Generally, in the WSS group, the soldering re- artefact. Due to this, destructive analytical techniques, such gion demonstrates slight Pb and Cu enrichments with a lower as TIMS or ICP-MS (e.g. Cattin et al. 2009; Ettler et al. oxidisation degree (Table 1,Figs. 5 and 6). 2015), may introduce a considerable error to the interpretation of results. This is because these techniques yield an average Lead isotopic characteristics of the provenance of raw result already in the course of sampling. In this paper, it is silver attempted at providing results of isotopic analyses taking into consideration changes of the so-called isotopic signature of One of the most important questions concerning the investi- the sample in the micro-scale. These changes may result from gated silver ornaments is the provenance of the raw material. It possible re-melting or heterogeneity of the raw material which Fig. 9 LDA showing the variability of a Ag, Cu, Bi, Au, Pb, Hg and O contents in the base surface of the archaeological types and b Ag, Cu, Bi, Au, Pb, Hg, Sn, Zn, Sb and O contents in the soldering area of the finds with granulations within archaeological types. Designations of the groups as in Table 1 6714 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 10 Scandinavian-type finds with wires from the Rajsków hoard presented in Fig. 3c as nos. 1 and 2 (Sc.R type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual finds from the group (zoom of Fig. 9b) was used. The isotopic analysis which is offered below was visible as a significant peak width, or the kernel function has divided into two areas—an analysis within technological several local maximums (see Fig. 16), one can suspect that the groups and a provenance analysis. In the latter case, geologi- silver was re-melted (Merkel 2016; Eniosova 2009;Eniosova cal data (as means) was taken from the available literature and Mitoyan 2011). Such a situation has been observed in all (Ettler et al. 2015;Merkelet al. 2013;Hatz et al. 1991). In the studied artefacts. both cases, all LA-ICP-MS results were taken into consider- Figure 17 and Table 4 (see also the Electronic supplement, ation for the artefacts. Furthermore, linear discriminant analy- 2. Linear Discriminant Analysis – Ornaments) offer an LDA sis was applied to search for differences between groups for lead isotope ratio distribution in four technological groups. 206 207 207 204 208 the following values: Pb /Pb ,Pb /Pb and Pb / The analysis demonstrates that the raw material is similar with 206 206 207 208 206 Pb , aswellasPb /Pb and Pb /Pb in the case of regard to its isotopic ratios in almost all the examined groups. the provenance analysis. Data obtained from the LDA confusion matrix demonstrates Moreover, a KDE model (Baxter 2003, 2016)proved use- that the highest lead isotope homogeneity can be seen in the ful, as it allows to create a continuous function describing the case of the West Slavic ornaments from Rajsków (WSR) probability distribution of the lead isotopic ratios being an (89% correct classifications). The percentage of correct clas- effect of the heterogeneity of metal in the examined artefacts. sifications is much lower for post-Moravian ornaments (mere- An example of such a model is presented in Fig. 16. ly 35%), while no correct classification was obtained for Having analysed lead isotopic ratios presented as Scandinavian ornaments and West Slavic ones from scatterplots and using the kernel density estimation of these Słuszków. ratios, one can draw conclusions about the provenance of The LDA (Fig. 18, see also the Electronic supplement,5. silver in the sample. If the values of lead isotopic ratios change Linear Discriminant Analysis—Provenance, Confusion ma- in one direction continuously from point to point, which is trix for the training sample) of the geological data Fig. 11 Round pendant (Fig. 3c, no. 2) from the Rajsków hoard, Scandinavian type—general view and SEM-SE images of the soldering region Archaeol Anthropol Sci (2019) 11:6705–6723 6715 Fig. 12 Post-Moravian–type finds with granulations from the Rajsków hoard presented in Fig. 3a as nos. 1–4(PM type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual artefacts from this group (zoom of Fig. 9b) demonstrates a strong similarity between ores. Out of 17 de- obtained. Not surprisingly, the metal in the artefacts was most- posits, a reasonable percentage of correct classifications was ly attributed to those deposits which were clearly different obtained in four cases only. The following deposits are clearly than others. different from others: Afghanistan, Freiberg (Germany) and Furthermore, these results demonstrate that the metal in a the Tatro-veporit unit (Slovakia)—100% of correct classifica- given artefact may be of different origin (see Electronic sup- tions. There is also a good isolation for Uzbekistan (76% of plement, 5. Linear Discriminant Analysis—Provenance, correct classifications). The assemblages of Rammelsberg Results for the prediction sample). This supports the assump- (Germany), Gammersham (Germany) and Neo-volcanic de- tion of re-cycling and re-melting of raw material from various posits are classified into the Tatro-veporit unit in 100% of sources. cases. The isotopic composition of samples from the Polish As it can be seen in Table 5 (see also the Electronic sup- deposits of Olkusz–Chrzanów–Pomorzany (marked as plement, 5. Linear Discriminant Analysis—Provenance, OlkChPom) and the Slovak deposit of Gemer is also similar Results for the prediction sample, and 6. Summaric results to the Slovak Tatro-veporit deposits. for provenance), the isotopic composition in individual groups This rather poor separation of deposits on the basis of Pb results from the fact of mixing of the raw material from isotopic ratios strongly influences the results of provenancing Central Asian (Afghanistan and Uzbekistan), German attempts. Results of 701 analyses on the discussed artefacts (Freiberg) and Polish ores. Interesting conclusions can be were processed by LDA, but in most cases (see Electronic drawn from the analysis of individual groups. In all Slavic supplement, 5. Linear Discriminant Analysis—Provenance, groups (that is, both West Slavic and post-Moravian), there Results for the prediction sample), no clear attribution to any is a preponderance of Freiberg silver over that from deposit was achieved. It was conservatively assumed that a Uzbekistan and Afghanistan (if considered separately). classification could be considered reliable when the prediction However, it seems that in total the Asian raw material still of probability was at least 70%. Thus, only in 250 cases (that played the most important role (Merkel 2016; Eniosova is, 36%), a more or less unambiguous classification was 2009). There are also some differences between groups of Fig. 13 Raspberry pendant (Fig. 3a, no. 2) from the Rajsków hoard, post-Moravian type—general view and SEM-SE images of the soldering region 6716 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 14 West Slavic–type finds with granulations from the Rajsków hoard presented in Fig. 3b as nos. 1–6 (WSR type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual finds from the group (zoom of Fig. 9b) Slavic jewellery concerning the share of individual deposits. whose isotopic composition may be similar to those which What is most striking, however, is a very different proportion were included into the analysis. of metal from various sources in Scandinavian jewellery. The share of European deposits is 32%, while nearly 70% of metal seems to have come from Asian sources. Of course, these Discussion observations must be treated with care. First of all, the number of the examined artefacts was not very high, which may pose Jewelleries craft problems for the statistical representativeness of results. Furthermore, the aforementioned rather poor separation be- A significant part of the investigated jewellery from the tween individual deposits must be taken into consideration. Rajsków and Słuszków hoards is granulated. The results show Last, but not least, a problem of missing sources must be borne that these elements are permanently bonded to the substrate by in mind. That is, the LDA-based statistical processing of data the process based on the use of copper compounds (Kolářová will classify given observations only to those deposits which et al. 2014). The properties of solder based on Ag–Cu are are present in the assemblage. Silver which was used in the widely described in Nature (Ashkenazi et al. 2017). discussed artefacts could also come from other deposits, Intentional doping of silver with copper up to 2.6 wt% Fig. 15 West Slavic–type finds with granulations from the Słuszków hoard presented in Fig. 2 as nos. 1–5 (WSS type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual artefacts from the group (zoom of Fig. 9b) Archaeol Anthropol Sci (2019) 11:6705–6723 6717 207/206 208/206 Fig. 16 KDE calculated (surface plot of a scatterplot) for lead isotope ratios Pb and Pb for two artefacts from the Rajsków hoard as an example of re-melted samples (Ashkenazi et al. 2017) causes the melting point of Ag–Cu decoration is more problematic for filigree jewellery and gran- alloy to be lower than 961 °C for pure Ag (Tuah-Poku et al. ulation. When melted, the solder is not absorbed into the sur- 1988;Bastow 2013). From an old handbook (twelfth century face and forms a Bpuddle^ in which small decorative elements receipts of Theophilus Presbyter; Pliny 1929; Leyden Papyrus melt (Eilbracht 1999). This type of soldering has been identi- fied by Macháček et al. (2016) during their study of the Great X), two types of soldering—metallic and non-metallic (chemical)—are known. These were discussed in detail by Moravian jewellery and on the ornaments from the BLumbe Duczko (1985,p. 26–28). Garden^ cemetery at Prague Castle (Ottenwelter et al. 2014,p. Metallic solders known from the third century BC are mix- 283). In line with what was said above, the spilled granulation tures of two or three metals (Wolters 1978,p. 5; 1983,p. 62). (see Figs. 5 and 6) with higher contents of Pb and Cu (added While silver artefacts are soldered, the main component is Ag, as a joining Ag-based mixture) in the soldering area (Table 1) while other additions could be gold, brass or tin (Wolters is characteristic for the beads from Słuszków hoard. The beads 1978, 1983, p. 61ff). The obtained soldering effect is not ar- are remarkable for their relatively ungrouped granules, so the tistically convincing. The solder mixture covers the entire sur- assumption concerning the application of metallic soldering is face between the ornaments and the base surface (Carrol 1974, justified. The granules are tiny (300–400 μm) and the solder is p. 35; Kolářová et al. 2014). The use of metallic soldering is spilled over all the surface (see LDA: Table 3, Fig. 10a). Apart particularly advantageous when joining larger and more dura- from that, the shape between granules which are close to each ble jewellery items. However, using metal solder for other is fuzzy (see Fig. 5). The WSS group soldering area is strongly different from that in the remaining jewellery under study (Fig. 9b, Table 3). The remaining part of the examined jewellery with granu- lation and filigree from Rajsków (post-Moravian and West Slavic types) and Stojkowo (Scandinavian type) demonstrates traces of use of the non-metallic (chemical, bonding) solder- ing. Non-metallic solders consist either of mineral or artificial- ly produced copper compounds (Duczko 1985). Written sources described a few such substances: malachite (in antiq- uity called chrysocolla) and azurite, naturally occurring forms of basic copper carbonate; patina (i.e. a copper alloy resem- bling enamel covering old bronze artefacts—mostly copper carbonate, containing natural oxides and oxides of bronze additives—tin, lead, zinc, arsenic); verdigris, a mixture of ba- sic copper acetate and copper acetate pentahydrate, produced by the action of vinegar on copper; and Roman vitriol, cupric sulphate pentahydrate (Tamla 2016). In order to prepare a 206 207 207 204 208 206 Fig. 17 LDA showing Pb /Pb ,Pb /Pb and Pb /Pb diffusion agent, a copper compound is added to a mixture of variabilityinfour groupsofornaments 6718 Archaeol Anthropol Sci (2019) 11:6705–6723 Table 4 LDA confusion matrix From/to PM Sc.R WSR WSS Total % correct for the training sample. Data obtained for lead isotope ratios: n (%) 206 207 207 204 Pb /Pb ,Pb /Pb and 208 206 Pb /Pb in the jewelleries’ PM 58 (35%) 0 (0%) 107 (65%) 0 (0%) 165 (100%) 35 groups Sc.R 5 (7%) 0 (0%) 65 (93%) 0 (0%) 70 (100%) 0 WSR 32 (11%) 0 (0%) 266 (89%) 0 (0%) 298 (100%) 89 WSS 25 (15%) 0 (0%) 142 (85%) 0 (0%) 167 (100%) 0 n number of measurements Fig. 18 LDA showing Pb / 207 208 206 Pb and Pb /Pb variability for geological data (means) ob- tained from the literature Archaeol Anthropol Sci (2019) 11:6705–6723 6719 Table 5 Results of LDA ore Number of Prediction Prediction Prediction Prediction Prediction provenance classification for four analyses Freiberg Uzbekistan Afghanistan OlkuszChPom Gammersham jewelleries’ groups WSS 68 25 (37%) 18 (26%) 18 (26%) 6 (9%) 1 (1%) WSR 90 27 (30%) 31 (34%) 22 (24%) 10 (11%) 0 (0%) PM 73 28 (38%) 22 (30%) 14 (19%) 9 (12%) 0 (0%) Sc.R. 19 5 (26%) 10 (53%) 3 (16%) 1 (5%) 0 (0%) Total 250 85 (34%) 81 (32%) 57 (23%) 26 (10%) 1 (0%) an organic adhesive (e.g. gum tragacanth, gum acacia, fish- processing of gold, silver and copper. Burning charcoal main- glue) and water. Sometimes, such mixture is enriched by so- tains a temperature of 800 °C without an artificial air supply. called asem described by Leyden Papirus X (Demortier et al. The temperature increases to 1300 °C when air is supplied 1999). The nature of asem is unknown, but this term is used in through a single pair of bellows or a blow-pipe (tools primar- an old handbook with reference to a substance whose proper- ily required for minor soldering operations). If there is a con- ties are similar to precious metals (Berthelot 1889). With this tinuous blast from water-powered double bellows, the temper- solution, the decorative elements are fastened to the substrate, ature rises as high as 1650 °C (Untracht 1985). The other and the artefact is then heated (Wolters 1983). property of charcoal is the ability to create a reducing atmo- In reference to what was said above, the granulation and sphere, which protects the heated metal from oxygen in the air. wire-ornamented West Slavic (WSR), post-Moravian type This is important due to the presence of copper and other (PM) and Scandinavian finds from the Rajsków hoard show easily oxidising elements (such as zinc, tin, antimony in our Cu, Sn and Sb (see Table 1) enrichments with a higher oxida- cases) in solder alloys. When heated, those elements produce tion degree in the soldering area (see Figs. 7, 8, 11 and 13). oxides, which coat the surface of the artefacts, thus preventing ThecontentofCu(whichisameltingagent)isupto the completion of the soldering process, which is visible in 57.3 wt%. This gives a melting temperature over 779 °C (a Figs. 7, 8, 11 and 13. If charcoal fire is not sufficient to lower value occurs for 28.1 wt% Cu) (Ashkenazi et al. 2017). completely eliminate oxidisation, it is necessary to use a spe- The soldering regions of all three archaeological types from cial anti-oxidisation agent, called flux which coated all the the Rajsków hoard are similar (see Fig. 9b, Table 3). These are joints. The following substances could be used as flux: soda characterised by a good separation from the base surface (see (sodium bicarbonate NaHCO ), tartar (potassium bitartrate Tables 1 and 2). Furthermore, the bonding area with a higher KC H O ), alum (hydrated potassium aluminium sulphate 4 5 6 content of copper (Cu) is enriched in low-melting elements Kal(SO ) ∙12H O), potash (potassium carbonate K CO ) 4 2 2 2 3 (Sn, Sb, Zn; Baxter 2003). These were presumably intention- and the most important factor, that is, borax (sodium ally added to the alloy as asem in diffusion bonding or as part tetraborate Na B O ). All these substances are well docu- 2 4 7 of a Cu-based mixture. The oxidation of the soldering region mented in historical sources (Wolters 1978). is correlated with the presence of Cu and Zn in post- Furthermore, the presence of Zn and Sb in the joining mix- Moravian–type artefacts (see Fig. 12a), with the presence of ture can be associated with the use of such minerals as Sb, Cu and Sn in West Slavic finds (see Fig. 14a) and with the tetrahedrite ([Cu,Fe] Sb S )(Munoz etal. 2015), which is 12 4 13 enrichment in Sb and Sn in Scandinavian finds (see Fig. 15a). also a source of copper, and sphalerite (ZnS). The latter is Generally, the presence of the oxide structure in the joining often found with Ag-rich galena deposits (PbS) which were region, around the granules and wires, could result from the main source of silver in medieval Poland and Europe (Gale enough reducing atmosphere during the chemical soldering and Stos-Gale 2000; Chamberlain and Gale 1980). or could be an effect of improper heat treatment. If soldering Furthermore, antimony is associated with freibergite mineral is to be successful, it is essential for the metal surfaces to be [Ag (Cu Fe )Sb S ] which characterised Freiberg 6 4 2 4 13–x absolutely clean. This is because a series of thermal treatment (Germany) silver ores based on galena and sphalerite boards. reactions occurs during this process: at 100 °C, CuO is formed Antimony-rich deposits were also located in Poland in Lower from Cu compounds; at 600 °C, the reducing atmosphere is Silesia, e.g. in Dębowiny in the Beskidy Mountains between created by glue carbonising; and at 850 °C, Cu oxides are Srebrna Góra and Złoty Potok (Mączka and Stysz 2008). In reduced to Cu by CO (Duczko 1985, p. 25). Heating above the Early Middle Ages, silver was extracted in this region by a 900 °C causes the metallic copper to diffuse to the base sur- refining process called cupellation. The aforementioned min- face and to the alloy of ornaments (Wolters 1983, p. 57). erals which may have been a source of elements used to pro- Charcoal fuel was used as a temperature agent. It has certain duce soldering mixture could be added as asem part to resin properties which render it particularly suitable for soldering glue being a binder in non-metallic soldering. Moreover, with operations. It generates high temperatures necessary for the regard to the antimony content, we may assume that our 6720 Archaeol Anthropol Sci (2019) 11:6705–6723 ornaments were made of silver from cupellation directly asso- heat and then it dripped from the upper to the lower pot. The ciated with this element. An important thing in the cupellation resulting purified antimony sulphide is the modern commer- process is wasting of silver by evaporation and dissolution of cial “crude antimony” or “grey antimony” (Agricola 1912,p. silver in lead oxide (PbO) and later soaking into a cupel (al- 428). kaline—for example from animal bone bound with potash). In the case of mercury content in all studied artefacts, this An optimal amount of lead must be selected—and this already element was widely used in workshops working with precious shows the quality of the workshop (the same as the tempera- metals, especially gold. Vitruvius in his work “On architecture ture of the furnace, the amount of copper admixture and the ...” (Agricola 1912, p. 123) said: “Mercury is suitable for quality of the cupel itself). Also, a significant influence on many purposes. Without it, you can not gild either silver or silver wasting is exercised by the addition of antimony and bronze [...] mercury attracts all gold particles and connects tellurium which facilitate silver infiltration into the cupel. If with it.” Theophilus (1979) in his recipes recommends it, the addition of these elements actually took place in order to among others, as an additive for grinding gold or silver (five produce raw silver of the studied jewelleries, antimony would parts of mercury and six parts of silver), for obtaining the so- be present in the entire artefact and not only in the solder called sand (extracted from the sand mined on the banks of the region. Rhine) or as an alloy for casting tin vessels (one quarter pound From “De Re Metallica” of Agricola (the work is of a of tin for one pound of tin) and final polishing of these castings sixteenth century date, but it also discusses much earlier tech- (a mixture of dissolved tin chips in mercury). Therefore, the nologies), we learn that the stibium mineral (probably presence of gold and mercury in the results of research on the antimonite or other antimony minerals) was used, among ornaments is probably not intentional (traces after amalgam others, for the metallurgical process of recovering gold from gilding) but results from contamination, for example, with pyrite. Excepting reduction with silver, and separation with components of a solder or alloy intended for granulation. nitric acid and a method of reduction with lead and silver, followed by cupellation and parting with nitric acid is the third Assessing provenance method that can be isolated. Yet another method is the reduc- tion with lead or antimony, followed by cupellation. The use When analysing the origin of the raw material, it should be of sulphur or antimony sulphide would tend to part out a remembered that metal artefacts are not geological ores. The certain amount of silver and thus to obtain fairly pure bullion objects are created by a series of anthropogenic actions, such upon cupellation. as extraction of raw metal, re-cycling or alloying with other Silver was also parted from gold by means of stibium. The metal. These actions cause the artefact’s structure to be het- use of antimony sulphide to part silver from gold is based erogeneous in the micro-scale. This is reflected in the hetero- upon a greater affinity of silver than antimony to sulphur. geneity of the chemical composition–elemental and isotopic Thus, the silver, as in other processes, is converted into a character of the artefact (Liu et al. 2018). Therefore, the mea- sulphide and is absorbed in the regulus, while the metallic sured composition is merely a resultant of an average of the antimony alloys with the gold and settles on the bottom of composition. For this reason, the interpretation of the obtained the pot. This process has several advantages over the results may be burdened with an error, and it should be treated sulphurisation with crude sulphur; antimony is a more conve- as a subject for further verification. Furthermore, it could be nient vehicle of sulphur, for it saves the preliminary suggested that apart from Pb, other isotopic ratios may also be sulphurisation with its attendant difficulties of volatilisation of use, for example Cu and Ag (Desaulty et al. 2011). Quite of the sulphur; it also saves the granulation necessary in the promising results have recently been obtained in iron prove- former method; eventually, the treatment of the subsequent nance studies which employed Os isotopic signatures products is simpler. (Dillmann et al. 2017, with further reading). The process in this description can be divided into six op- Three phases of silver inflow are isolated for Poland in the erations: (a) sulphurisation of the silver by melting it with Early Middle Ages (tenth to twelfth century). In the first phase antimony sulphide; (b) separation of the gold “lump” which falls within the pre-state period (to the end of the tenth (massula) by jogging; (c) re-melting the regulus (mistura) century), there is a preponderance of oriental silver, chiefly three or four times for a recovery of further “lumps”; (d) re- Arab dirhams (Burâkov 1965, 1974; Bubnova 1963;Cowell melting of the “lump” four times, with further additions of and Lowick 1988;Dekówna 1971,p.496,487;Merkel 2016; antimony sulphide; (e) cupellation of the regulus in order to Eniosova 2009; Eniosova and Mitoyan 2011). For about recover the silver; and (f) cupellation of the antimony from the 250 years (since the eighth to the mid-tenth century), dirhams “lump” to recover the gold (Agricola 1912,p. 451). are the main component of hoards found in Poland. This The method described by Agricola for treating antimony changes in the second half of the tenth century, when sulphide was still in use in the twentieth century in the Harz, in Western European coins and then local issues commence to Bohemia and elsewhere. The stibnite was liquated out at a low prevail. This second wave of inflow (second half of the tenth Archaeol Anthropol Sci (2019) 11:6705–6723 6721 to late eleventh century) was related to a dominant role of However, at present, it is difficult to compare all previously coins which were coming to Poland from Western European published studies (Gójska et al. 2019)—most of the performed countries, chiefly from Germany, where enormous deposits of analyses were obtained by X-ray fluorescence spectrometry silver were discovered in the Harz in the Rammelsberg mine (XRF) or X-ray microanalysis spectrometry (EDX) on sur- in the third quarter of the tenth century (Jammer 1952,p. 62; faces (often corroded or contaminated), which may produce Suchodolski 1971, p. 22). The third phase is related to the use distorted results. This method is not accurate when examining of native silver and is well visible in finds since the rule of the raw material of the base surface, and the solder area is Bolesław Krzywousty (1107–1138). usually analysed along with the entire metal surface, which Due to the technological nature of the artefacts, i.e. their can distort the quantitative reading of elements (Ottenwelter heat treatment and a considerable blur of intentionally added et al. 2014). Nevertheless, studying ornaments by surface layers, there seems to be little point in attempting at techniques we obtain preliminary information about their interpreting the elemental composition in relation to the com- structure and chemical composition. In order to compare the position of individual geological deposits. More so, because raw material of alloys and silversmiths used in early medieval the discussed silver deposits are PbS and ZnS systems with Europe, it is necessary to continue systematic archaeometric similar additives. What is remarkable is the aforementioned research on similar ornaments, also with the use of invasive presence of Sb in the deposits from Freiberg and from Lower preparation (Kolářová et al. 2014) in order to establish a da- Silesia. The percentage share of individual elements in the tabase of comparative data. artefacts does not reflect the initial composition of the deposit, Studies on aesthetically and technologically advanced ar- which was first extracted from the ore. Then, the obtained raw tefacts from the Early Middle Ages reveal a completely new material was melted and intentional additives were added in aspect of the Slavic culture and are the basis for undertaking order to receive the desired technological parameters. international cooperation in methodological research on sim- The results of the Pb isotope ratio study provide grounds ilar finds from the Czech Republic and Scandinavia. for concluding that the silver used to produce the discussed Submitted results confirm a crucial role played by different early medieval artefacts comes from different sources and ores complementary analytical techniques, in particular SEM- (Table 5). This means that the investigated ornaments may EDX, LA-ICP-MS and also lead isotope ratios and statistical have been made of silver coming from various other artefacts methods in order to identify combined techniques used in and ores. The results of our investigations may suggest the silver ornaments and to establish the origin of the raw silver used for manufacturing the discussed jewellery chiefly material. originated from Asia (Uzbekistan and Afghanistan) or Funding information This work was has been carried out with the finan- Freiberg in Germany. cial support of the National Research Centre in Cracow, Poland (grant no. UMO-2013/09/B/HS3/03289). Conclusions Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// The obtained results provide detailed information about the creativecommons.org/licenses/by/4.0/), which permits unrestricted use, technological aspects of early medieval silver ornaments from distribution, and reproduction in any medium, provided you give Central and Eastern Europe and allow for an isolation of two appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. types of soldering. In the future, on the basis of studies on larger assemblages, it may be possible to propose a new and more relevant archaeological classification of these finds. This classification can be regarded as valid after a thorough exam- References ination and comparison of all the studies of ornaments from other West Slavic and Scandinavian territories. Research on Agricola G (1912) De Re Metallica. Translated from the first latin edition jewellery allows to introduce the Slavic tradition to the art of 1556 by Hoover HC and Hoover LH.: London Ashkenazi D, Gitler H, Stern A, Tal O (2017) Metallurgical investigation history and material culture of Europe. Until now, this tradi- on fourth century BCE silver jewellery of two hoards from Samaria. tion has been largely unknown to the world science due to the Sci Rep:1–14. https://doi.org/10.1038/srep40659 lack of relevant studies. So far, Polish scholars have made Ashkenazi D, Gitler H, Stern A, Tal O (2018) Archaeometallurgical char- only one attempt at solving the problem of similarity of tech- acterization and manufacturing technologies of fourth century BCE silver jewelry: the Samaria and Nablus hoards as test case. nological decorations in the Slavic territories. 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Nuc Inst Methods Phys Res B136–138:851– River), Warszawa Ottenwelter E, DědJ, Barčáková L (2014) Technical study of jewellery from the BLumbe Garden^ cemetery at Prague Castle. [in:] Frolík J Publisher’snote Springer Nature remains neutral with regard to ed.: Pohřebiště v Lumbeho zahradě na Pražském hradě. Díl II. jurisdictional claims in published maps and institutional affiliations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archaeological and Anthropological Sciences Springer Journals

Archaeometric studies on early medieval silver jewellery from Central and Eastern Europe

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Springer Journals
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Copyright © 2019 by The Author(s)
Subject
Earth Sciences; Earth Sciences, general; Archaeology; Chemistry/Food Science, general; Geography, general; Life Sciences, general; Anthropology
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1866-9557
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1866-9565
DOI
10.1007/s12520-019-00935-z
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Abstract

Scanning electron microscopy with X-ray microanalyses (SEM-EDX) was used for a technological study of silver jewellery from three hoards found in Poland. The assemblage consists of 26 artefacts from the period of formation of the first Polish state (900– 1039 AD) and can be divided into three groups: West Slavic, post-Moravian and Scandinavian. Research results provide information concerning techniques used for granulation ornament and the provenance of raw silver. Elemental composition changes are manifested mainly by different Cu contents. A higher Cu content was found in solder. The higher Cu content in relation to the morphology of the joining region with visibly spilled granulation demonstrates that the West Slavic beads were produced with the use of metallic soldering. On the other hand, other studied jewelleries are characterised by Cu, Sn, Sb and Zn enrichments in oxidised soldering regions, which implies that they were manufactured with the use of non-metallic soldering. In addition, studies on the provenance of the raw material were made based on the analysis of lead isotopic ratios. For this purpose, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used, and the obtained lead isotopic ratios were processed using linear discriminant analysis (LDA). The isotope study demonstrates that all examined artefacts were made using re-melted metal from multiple sources. The most probable sources of silver were ores from Uzbekistan, Afghanistan and Freiberg (Germany). . . . . Keywords SEM-EDX LA-ICP-MS Lead isotope ratios Medieval jewellery Silver hoards Introduction Poland (Dekówna 1974; Zoll-Adamikowa et al. 1999). Assemblages consisting of coins and other kinds of silver arte- The aim of this paper is to discuss the results of recent research facts are important historical source materials from which it is conducted on female ornaments from early medieval hoards in possible to obtain data about economic, political and social conditions of people who were depositing silver. These issues are crucial for understanding the relations between early states Electronic supplementary material The online version of this article in Central Europe, mainly between the first Polish state created (https://doi.org/10.1007/s12520-019-00935-z) contains supplementary by the Piast Dynasty, the Czech state and Scandinavian coun- material, which is available to authorized users. tries. The custom of deposition of silver and gold artefacts in the form of hoards was of Scandinavian origin and went into use in * Ewelina Miśta-Jakubowska Ewelina.Mista@ncbj.gov.pl Piast Poland, but not in the Czech lands ruled by the Přemyslid Dynasty. The hoards, consisting of coins and ornaments, usu- 1 ally hacked into pieces, appear in the realm of the Piasts for the National Centre for Nuclear Research, A. Sołtana 7, first time in the mid-tenth century, and their number gradually 05-400 Otwock, Poland 2 increases until the custom of hoard deposition disappears in the Institute of Archaeology and Ethnology, Polish Academy of beginnings of the twelfth century (Jakimowicz 1933; Sciences, Al. Solidarności 105, 00-140 Warsaw, Poland Kostrzewski 1962). The ornaments from these hoards are cov- Institute of Nuclear Chemistry and Technology, Dorodna 16, ered with granulation, which was a decoration with ancient 03-195 Warsaw, Poland traditions (see, e.g. Duczko 1985 Eilbracht 1999; Pliny 1929; Institute of History, Jan Długosz University in Częstochowa, Al. Theophilus 1979; Ogden 1982). Granulation was a favourite Armii Krajowej 36a, 42-200 Częstochowa, Poland 6706 Archaeol Anthropol Sci (2019) 11:6705–6723 ornamentation technique among craftsmen working for social 1980s (research on finds from Birka in Sweden) and did not elites in the first state of the West Slavs, that is, Great Moravia, contain detailed analyses of physico-chemical traits of in the ninth century AD. The origins of ornaments are to be discussed finds (Duczko 1972, 1984, 1985, 1986). This issue, searched in the traditions of Late Roman Art which survived in on a larger scale, is currently being researched by the authors the Byzantine Empire. Moravian ornaments, which are known as part of two grants in collaboration with the University of only from burials, are of very high quality and represent a Stockholm and the National Museum in Stockholm. special phenomenon in early medieval European art (Čáp et al. 2011;Galuška 2013). After the destruction of the Moravian state inthe earlytenthcenturybythe Hungarians, Material and methods Moravian goldsmiths moved in two directions: westward to the Czech state, and eastward to Kievan Rus, created and ruled by Archaeological material the Scandinavians. Each group of these craftsmen created their own repertoire of types characteristic only for them. In the This paper discusses the results of research on 26 ornaments hoards found in the territory of the Piasts, there is a prevalence from three early medieval silver hoards discovered in of ornaments typical for the Czech art, while ornaments of the Słuszków, Rajsków and Stojkowo in Poland (see Fig. 1). eastern group are known from hoards deposited by the Rus, i.e. The hoard from Słuszków (Kalisz District, Poland) is one of the Scandinavians living in Eastern Europe (Ukraine, Belarus the largest ones of such kind in Poland (see Fig. 2). It was and the European part of the Russian Federation). In the eastern discovered in 1935 during land adjustment. Today, the hoard hoards, post-Great Moravian ornaments were mixed with typ- is in the collection of the District Museum of the Kalisz Region. ical Norse jewellery, in which the techniques of filigree and The assemblage contains 13,061 finds, most of which being granulation were also employed. Post-Great Moravian orna- cross denars. The latest issues come from the end of the elev- ments hold a special place in the European history of art, be- enth and the beginning of the twelfth century. The most numer- cause of their own unique nature. As all jewellery, also those ous group in the hoard consists of cross denars of types I, II, IV, had religious and social functions (Duczko 2015, 2016, 2018). V, VI, VII and VIII. It includes 12,829 items, which is over 98% A few experimental technological studies were done of artefacts in the assemblage. In addition, the Słuszków hoard (Thouvenin 1971, 1973;Baines 2005) however, they did not also contains 32 granulated silver beads decorated with filigree cover physico-chemical properties of jewellery of such type. (25 items with bosses, 4 oval ones and 3 small fragments of Published results of contemporary studies on ornaments made silver sheet with traces of granulation), 7 silver ingots and 71 with the use of granulation and filigree techniques are mainly foreign coins: Arabic, English, Danish, German, Czech and focused on gold artefacts (e.g. Scrivano et al. 2013, 2017a, b; Hungarian, mostly preserved in fragments. However, the most Ontalba Salamanca et al. 1998; Šmit et al. 2000, Šmit and spectacular group in the hoard are Palatine Sieciech’s denars: Šemrov 2006). 120 items with a cross pattée and 1 + 2 with a monogram. It is A recent study by Ashkenazi et al. (2017, 2018)concerns the largest known assemblage of coins of this magnate. results of research on silver treasures whose chronology The second of the examined hoards was accidentally dis- strongly precedes the finds discussed in this article. In recent covered in 1992, when a residential building in the Kalisz- years, Czech researchers have commenced to fill this gap. Rajsków quarter was extended (see Fig. 3). Part of the hoard What can be mentioned here is a series of archaeological ex- is kept in the Kalisz Museum and it includes 636 finds with a periments on the technology of manufacture of early medieval total weight of 281.2 g. In this part of the hoard, 146 entirely ornaments from Great Moravia, with a special focus on fili- preserved oriental coins and their fragments (a fragment of an gree and granulation (Čáp et al. 2011). Another important Arab-Sasanian drachma from the end of the seventh century, work deals with the composition of metal, construction and and dirhams dated to the period between the end of the sev- technology of goldsmith decorations discovered at the enth and the end of the tenth century) were distinguished. BLumbe Garden^ cemetery at Prague Castle (Ottenwelter Furthermore, German denars and their fragments, including et al. 2014). Ornament analyses were carried out by scanning the earliest type I cross denars, Czech and Scandinavian coins, electron microscopy using X-ray dispersion spectrometry. Yet as well as issues of Bolesław Chrobry (type CNP 47) from the another valuable study is a monograph with a detailed discus- initial period of this ruler’s reign were present in the assem- sion on finds from Břeclav - Pohansko VII, including scan- blage. There are 490 fragments of ornaments in the hoard, of ning electron microscopy of Great Moravian jewellery from which 16 specimens were selected for archaeometric research. the Pohansko site (Macháček et al. 2016). The third early medieval silver hoard discussed in this pa- However, the early appearance of Czech ornaments in per was discovered in 1926 in a village of Stojkowo (Fig. 4), Europe did not attract enough attention from researchers. W. 10 km to the east of Kołobrzeg (Kolberg) and is deposited Duczko studied Danish Viking ornaments, including Slavic now in the National Museum in Warsaw. Only a part of it weighting about 740 g has survived, while the rest weighting artefacts. His first works were published in the 1970s and Archaeol Anthropol Sci (2019) 11:6705–6723 6707 Fig. 1 Map of finds of the silver hoards discussed in this paper about 400 g and a covered clay vessel in which the hoard far from adequate and precise (Kiersnowska and was buried were lost during the Second World War. The Kiersnowski 1955). preserved part consists of 102 coins (chiefly from German mints and 28 cross denars of types I, II, III, V, VI and Structural and elemental composition analyses VII), 9 lumps of cast silver or their fragments, 39 frag- ments of silver bars and silver sheets, 159 fragments of Before laboratory analyses, the artefacts were cleaned in silver sticks and wire and 152 various silver ornaments AVEL Silver Cleaner solution (http://www.avel.com/avel-33/ (parts of rings, temple-ring pendants, silver beads, chains, produit/293-silverware-avel-33.html, accessed on 2 August necklaces and buckles), mostly hacked and broken. 2017), and then they were bathed in acetone and air dried in Probably about 400 coins (mostly dirhams) and some oth- order to remove conservation layers. The conservation of the er artefacts, among them a few fragments of silver bars, jewelleries included mechanical cleaning, application of 5% were lost. Information concerning this lost part of the disodium edetate solution (Ślesiński 1995) and covering the hoard was obtained from literature. However, this data is surface with Paraloid B-72 acrylic resin (Costa 2001). The 6708 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 2 Silver beads from the early medieval hoard from Słuszków: West Slavic group. Photo: M. Osiadacz state of preservation of the finds was good and no corrosion The SEM-EDX study provided information about morpho- was observed. logical changes and allowed for a determination of the quan- SEM-EDX (scanning electron microscopy with X-ray mi- titative elemental composition in the micro-scale, taking spec- croanalysis) was the main technique which was used for the ifications of the solder region, base surface and granule com- study of technological changes in surfaces of the discussed positions into account. The granules and surface where they ornaments. This was due to the surface interaction of the ex- were attached by soldering are referred to as the base surface citation electron beam and a possibility of EDX signal regis- in the further part of this paper. This was due to their similar tration from near-surface layers (Gójska et al. 2019) in the elemental composition. For each technological area of a given region of soldering occurring up to about 30 μm from the artefact, at least n = 3 measurements were carried out. The surface (Kolářová et al. 2014). SEM-EDX analysis, described SEM-EDX analysis was done using a Carl Zeiss EVO in detail in Goldstein et al. (2007), is a popular non-destructive MA10 Scanning Electron Microscope equipped with an technique used in studies of archaeological finds (e.g. EDAX X-Flash Detector 5010 with a 123-eV spectra resolu- Scrivano et al. 2017a, b; Ontalba Salamanca et al. 1998; tion (Zeiss. Poland; www.zeiss.com) and provided with a Ashkenazi et al. 2017, 2018; Linke and Schreiner 2000, Bruker Quantax 200 Esprit 1.9 system for analyses of EDX Linke et al. 2003, 2004;Ingo etal. 2004;Miśta et al. 2017; spectra. The image analysis was carried out using a secondary Gójska and Miśta 2016). Twenty-six artefacts were tested electron detector (SE) with a resolution up to 2.0 nm. Other altogether. parameters were the following: accelerating voltage 20 keV, Fig. 3 Silver ornaments from the early medieval hoard from Rajsków: a post-Moravian group; b West Slavic group; c Scandinavian group. Photo: M. Osiadacz Archaeol Anthropol Sci (2019) 11:6705–6723 6709 Fig. 4 Silver ornaments from the early medieval hoard from Stojkowo: Scandinavian group. Photo: M. Osiadacz measurement time 120 s and LLD = 0.1 wt%. The current and density estimator (KDE) model was used to obtain a 3D mod- field magnification was adjusted to the type of morphology of el of lead isotopic ratio distribution in artefacts (Kulczycki each studied surface. The quantitative analysis was done using 2005; Baxter 2003, 2016; Everitt and Hothorn 2011;Everitt the non-pattern method with an error < 3% for the main ele- et al. 2011). ments and < 20% for traces below 1 wt%. Standard reference materials which were used for EDX result authentication were Ag and Cu alloy mixtures in all Ag/Cu % range (ESPI metals). Results Lead isotope analyses SEM-EDX analysis of technological changes Furthermore, an ore provenance study was carried out based in the surface of the ornaments on the results obtained for 20 ornaments. The micro-invasive LA-ICP-MS was carried out with an ELAN 9000 Inductively A series of 26 silver ornaments—18 made in filigree and Coupled Plasma Mass Spectrometer (Perkin Elmer SCIEX, granulation techniques (in one find from the Rajsków Canada: www.perkinelmer.com) equipped with an LSX- hoard—the artefact without no. in Fig. 3—the soldering area 200 laser ablation system (CETAX, USA: www.cetax. was not identified by the SEM-EDX analysis) and 8 without com). The LSX-200 combines a stable environmentally such decoration (the finds from the Stojkowo hoards, see in selected 266-nm UV laser (Nd-YAG, solid state, Q-switches) Fig. 4)—were examined. These artefacts belong to the West with a high sampling efficiency, variable 1 to 20 Hz pulse Slavic (12 finds—5from Słuszków, see Fig. 3,and7from repetition rate and maximum energy up to 6 mJ/pulse. The Rajsków, see in Fig. 3b), post-Moravian (4 finds from applicability of this technique in archaeological provenance Rajsków, see Fig. 3a) and Scandinavian (10 finds—2from analyses is briefly discussed by several authors (e.g. Baker Rajsków, see Fig. 3c, and 8 from Stojkowo, see Fig. 4)groups. et al. 2006;Budd etal. 1995;Hirata 1996; Stos-Gale & Gale The technological groups were isolated based on visual char- 2009). The NIST 981 reference standard material was used for acterisation according to Duczko (1985). quantitative determination of lead isotope concentrations (0. The surface morphology of all precious metal artefacts was 204/206 207/206 059042, 0.91464 and 2.1681 for Pb ,Pb and studied by SEM-SE. In the case of ornaments with granula- 208/206 Pb with relative standard deviation below 0.1%). tion, three technological areas were identified: 1—base sur- Measured median values (n = 78) with relative standard devi- face made of silver alloy; 2—joining zone located between the ation are 0.0610 ± 1.08, 0.0915 ± 1.02 and 2.1720 ± 1.16% for surface and the decoration; and 3—ornamentation on the base 204/206 207/206 208/206 Pb ,Pb and Pb , respectively. For each arte- silver alloy, e.g. granulation and twisted wire. fact, n = 40 measurements were carried out with SD: < 6% for Furthermore, on the basis of morphological differences in 206 207 208 206 207/204 Pb /Pb , < 7% for Pb /Pb and < 5% for Pb . the ornamentation zone which were identified by SEM obser- The obtained results of the elemental composition and lead vations, three types of joining were found: (i) spilled granula- isotope study were processed using principal component anal- tion ornaments, (ii) non-oxidised spherical granules and (iii) yses (PCA) and linear discriminant analysis (LDA). A kernel oxidised soldering area with spherical granules. 6710 Archaeol Anthropol Sci (2019) 11:6705–6723 All the analysed beads from Słuszków display similar char- Stojkowo hoard resemble Scandinavian-type artefacts without acteristics of the soldering area with the lack of extensive granulation (see Fig. 4). oxidised structure in the soldering region. Such structures as- What is important while analysing the results is that the sociated with two different solder types are presented in elemental composition determined for each technological part Figs. 5 and 6. Figure 5 (surface of find 2 from Fig. 2)offers is only approximate due to a considerable blur of the elements’ examples of SEM-SE images recorded for the first type of the distribution on the surface micro-regions. This results from the joining structure. This variety is characterised by granules fact that these ornaments were processed at high temperatures which are smoothly embedded in the surface. The size of these (Untracht 1985; Wolters 1983). In our study, the division into granules is about 300 μm (see Fig. 5). Moreover, the shape of the base surface and the soldering area was confirmed by the the granules is fuzzy and a significant merging with the solder linear discriminant analysis. Table 2 presents the results of structure can be seen. The ornament is spilled on the surface. LDA correct allocation for two selected (based on elemental Furthermore, in Fig. 6, one can see granules separated from composition in Table 1) technological areas. The greatest spill the solder layer which is characterised by the lack of extensive of solder over the surface is visible in the WSS type. Based on oxide structures. The size of these granules is about 400 μm the results presented in Table 2, the division shown in Table 1 (see Fig. 6). seems to be appropriate. Different technological types of joining areas were ob- As it can be seen in Table 1, the soldering area of the West served in the case of ornaments from the Rajsków hoard. Slavic artefacts from Rajsków is the most oxidised (O up to Figures 7 and 8 offer SEM-SE images of a micro-region with 51.4 wt%) with the highest concentration of copper (Cu) up to the granulation ornament. Cloudy shapes of joining structures 57.3 wt% and high tin (Sn) and antimony (Sb) contents. The between granules are visible with the size of the granules from solder in the post-Moravian jewelleries (see Figs. 7 and 8)is 300 (see Fig. 8)to 400 μm (see Fig. 7). similar with regard to the content of O, while it has a lower Cu Based on the SEM images, it can be said that the spilled content (up to 27.8%) and slightly higher Sn (up to 24.7 wt%), ornament (as discussed below) with relatively small size of the Pb (up to 7.0 wt%) and Sb (up to 19.5 wt%) concentrations. granules and the lack of oxide structures indicates the use of Concerning the solder type, all five beads from Słuszków metallic soldering (Ottenwelter et al. 2014;Macháček et al. are characterised by the lack of very oxidised structure (see 2016; Ferro et al. 2009) in the case of the beads from the Figs. 5 and 6) with the O content in the range from 3.3 to Słuszków hoard. The presence of oxide structure in the area 22.6 wt%. The Cu, Sn and Zn contents are also low, as com- of tiny granule assemblage in the finds from Rajsków could be pared with other types of jewelleries (see Table 1)withslight a chemical soldering effect (Čáp et al. 2011;Duczko 1985). Pb and Cu enrichment. The elemental composition study results confirm the above The soldering area of the Scandinavian jewelleries from assumption, as described below. Rajsków is enriched in Cu, Sn, Sb, Pb and O with regard to Furthermore, the EDX elemental composition of orna- their base surface. The base surface of the finds without gran- ments allowed to distinguish technological micro-areas within ulation from the Stojkowo hoard is different from other types three archaeological types. Ag, Cu, Bi, Pb, Zn, Sn, Au, Hg, Sb of the base surface (see Fig. 9a). It is enriched in Cu and Pb. and O concentrations above 0.1 wt% were identified as a Generally, the elemental composition differences determined normalised value. The results are presented in Table 1.The for all the types of jewelleries are presented graphically below, West Slavic and Scandinavian types were divided into two both as a difference in the content of elements in the soldering groups according to visual traits, i.e. beads from Słuszków areas (see Fig. 9b) and raw silver (see Fig. 9a)which was usedto have a different soldering area as shown by SEM analyses produce the base surface and ornaments. In the diagrams below, (see Figs. 5 and 6). On the other hand, the finds from the all EDX measurements were taken into account. Fig. 5 SEM-SE images of the surface of the silver bead from Słuszków (Fig. 2: no. 2) characterised by spilled granulation ornament. The technological parts are as follows: 1—base surface, 2—soldering area and 3—granules as part of the granulation ornament Archaeol Anthropol Sci (2019) 11:6705–6723 6711 Fig. 6 SEM-SE images of the surface of the silver bead from the Słuszków hoard (Fig. 2: no. 3), find 12683. Regular spherical granules without extensive oxidised solder area can be seen. Designations (1–3) as in Fig. 5 Figure 9 shows the results of the elemental composition accordance with what is offered in Table 2). The main classi- analysis presented as a LDA diagram (Baxter 2016, 2003; fication error occurs only in Fig. 15: point II. In all PCA Everitt and Hothorn 2011). The LDA confusion matrix can diagrams, the Ag content is correlated with the base surface, be found in Table 3. while Cu, Sn, Zn, Sb and Bi are related to the soldering region. As it can be seen in Fig. 9 and Table 3, the base surface However, as reported by Kolářová et al. (2014), the registered regions in all types of jewelleries with granulations are similar EDX signal gives information about the base surface contam- concerning their elemental composition. A better separation inated by solder components (Wolters 1983). (61%) is observed for the artefacts without granulations from In Fig. 10, in the soldering area, there are two notable the Stojkowo hoard. Furthermore, in the case of the soldering anomalies with higher Cu (up to 29.5 wt%), Sn (up to area, a better allocation to the group can be seen for WSS 8.8 wt%), Sb (up to 4.6 wt%) and O (up to 56.5 wt%) contents. (72%), WSR (54%) and Sc.R (50%). The soldering regions They concern find no. 2 in Fig. 3c. The SEM-SE images of the of PM jewelleries are similar to all other types and the alloca- soldering region of this pendant can be seen in Fig. 11.In turn, tion to the predicted group is 30%. Figures 10, 12, 14 and 15 the composition of this joining area is slightly similar to what illustrate a graphical distribution of variability of Ag, Cu, Bi, occurs in the WSR and PM type (see Fig. 9b). Au, Pb, Hg, Sn, Zn, Sb and O concentrations. In the diagrams, The largest anomalies within the soldering area are present there are marked areas (respectively, I–II, a–c) with composi- in the PM group, which is also evidenced by the LDA results tion anomaly in the groups in question. Figures 10b, 12b, 14b presented in Table 3 (only 30% of correct allocations). There and 15b (as a fragment of Fig. 9b) present LDA separation of are observed anomalies in the concentration of low-melted the soldering area for each artefact within archaeological elements such Pb, Sn, Zn, Sb, Bi and Cu. These anomalies groups. Numerical designations of the finds are explained in can be seen in the case of finds nos. 2 (no a, b, I in Fig. 12)and Figs. 2 and 3. Moreover, the a) parts of Figs. 10, 12, 14 and 15 4 (no c, II, III in Fig. 12)fromFig. 3a.The firstone is contain PCA correlation-type diagrams presenting the results characterised by a much higher content of Sb (up to of the elemental composition analyses of the soldering region 19.5 wt%), Sn (up to 24. 7 wt%) and Cu (up to 27.8 wt%) and the base surface in each technological group. with higher Pb, Zn and O concentrations. The other one is Generally, as it is shown in the PCA diagrams from panels characterised by the oxidised soldering region (up to a of Figs. 10, 12, 14 and 15, the division into the base surface 50.4 wt%) with higher Cu and Sn concentrations, as it can and the soldering region within a given archaeological group be seen in Fig. 7. In the PCA diagram (Fig. 12a), there are based on the elemental composition is justified (which is in strong Sn–Sb and Zn–Cu correlations, which means that these Fig. 7 SEM-SE images of the surface of the silver bead from the Rajsków hoard (see Fig. 2: no. 4). An oxidised solder area and regular spherical granules can be seen. Designations (1–3) as in Fig. 5 6712 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 8 SEM-SE images of the granulation area of the silver bead surface from the Rajsków hoard (see Fig. 2: no. 1). There are oxidised soldering structures (2) located in the space between granules (3) components could be added in this substrate correlation to the earring with filigree (Fig. 3b: no. 6, WS type); an earring (PM joining mixture. Figure 13 shows the soldering region of the type); a round pendant (Sc type); and a raspberry pendant (PM abovementioned pendant marked as no. 2 in Fig. 3a. type)—a slightly increased content of gold and mercury was The raspberry pendant presented below is an example of an detected in the micro-region. ornament characterised by higher contents of low-melted ele- The soldering region of the WSR group is characterised by ments in the oxidised solder areas. Moreover, a higher per- 54% allocation to the correct group with a high (31%) alloca- centage of gold (Au) up to 2.7 wt% and mercury (Hg) up to tion to the PM group (see Table 3). The two anomalies are 2.4 wt% was recorded in the entire artefact. Generally, for the observed for two artefacts: nos. 2 (see point I in Fig. 14)and 3 entire assemblage from the Rajsków hoard, the mercury en- (see point a in Fig. 14)fromFig. 3b. Generally, the entire richment (up to 4.0 wt%) is mainly observed for the base soldering area of the WSR group is oxidised and characterised surface, but in some cases, it is also related to the soldering by the positively correlated Sn, Cu and Sb contents, while in region. For five ornament fragments—a bead with a bump, the PM group there is the oxidised soldering area with corre- WS type (see Fig. 3b: no. 2, see Fig. 14 below point I); a starry lated Cu–Zn and Sb–Sn contents (see Fig. 12). Moreover, the Table 1 SEM-EDX analysis results Arch. type Hoard Tech. area (wt%) Ag Cu Bi Au Pb Hg Sn Zn Sb O West Slavic Słuszków (WSS), Base surface Av. (n = 37) 87.8 3.4 0.7 0.7 0.7 0.7 0.1 0.1 < 0.1 6.0 5obj. Δ 72.6–95.6 < 9.5 <3.4 < 4.7 <3.4 <3.1 <1.1 <1.0 < 0.1 1.2–16.0 Soldering area Av. (n = 21) 79.5 6.7 1.3 0.9 1.7 0.9 0.3 0.2 0.1 8.5 Δ 63.1–88.7 2.4–11.0 <5.0 < 4.2 <6.3 <2.8 <1.7 <0.9 < 0.9 3.3–22.6 Rajsków (WSR), Base surface Av. (n = 42) 88.8 3.9 0.4 0.6 0.5 0.5 0.3 < 0.1 < 0.1 4.8 7obj. Δ 69.3–95.7 2.3–9.4 < 3.0 < 3.4 < 3.5 < 2.8 < 2.1 < 0.1 < 0.1 < 20.7 Soldering area Av. (n = 26) 33.4 23.0 1.0 0.7 1.0 0.6 3.9 0.5 2.2 33.7 Δ 2.2–87.6 3.4–57.3 < 9.5 < 6.2 < 6.6 < 3.8 < 18.6 < 2.3 < 13.1 4.3–51.4 Post-Moravian Rajsków, (PM), Base surface Av. (n = 41) 87.9 3.2 0.9 1.0 0.3 1.1 0.1 0.1 < 0.1 5.6 4obj. Δ 75.8–99.0 0.5–6.0 < 4.0 < 3.2 < 2.8 < 4.0 < 1.4 < 0.7 < 0.1 < 18.4 Soldering area Av. (n = 30) 50.6 12.7 1.1 1.2 1.7 0.9 4.9 0.5 2.3 24.2 Δ 4.9–75.7 4.4–27.8 < 5.4 < 3.1 < 7.0 < 3.4 < 24.7 < 2.3 < 19.5 9.3–50.4 Scandinavian Rajsków Base surface Av. (n = 8) 90.2 3.2 0.2 0.6 0.3 1.1 0.2 0.1 < 0.1 4.2 (Sc. R), 2 obj. Δ 83.4–96.3 1.4–6.1 < 1.5 < 3.4 < 1.6 < 2.2 < 0.7 < 0.6 < 0.1 1.4–7.7 Soldering area Av. (n = 9) 58.3 11.8 0.6 1.5 1.6 1.2 2.8 0.2 1.1 20.9 Δ 5.0–80.1 4.6–29.5 <3.5 < 4.9 <4.8 <2.7 <8.8 <1.1 < 4.6 8.3–56.5 Stojkowo Base surface Av. (n = 31) 84.9 6.0 1.2 0.8 1.4 0.7 < 0.1 0.4 < 0.1 4.6 (Sc. St), 7 obj. Δ 60.6–92.2 2.8–17.3 <3.1 < 2.3 <3.5 <2.7 <0.6 <1.3 < 0.1 0.7–21.2 n number of measurements, Δ range of composition variation for the technological area Archaeol Anthropol Sci (2019) 11:6705–6723 6713 Table 2 Part of the LDA confusion matrix for the training sample Table 3 LDA confusion matrix for the training sample. Data obtained showing correct allocation for the technological areas of the for the base surface and the soldering area of jewelleries groups archaeological types (two training sets/technological group—base sur- From/to Sc.R Sc.St PM WSS WSR face and soldering area; 10 variables: Ag, Cu, Bi, Au, Pb, Hg, Sn, Zn, n (%) Sb, O) Correct allocation: n (%) Base surface Soldering area Base surface (as in Fig. 9a) Sc.R 2 (25%) 2 (25%) 2 (25%) 0 (0%) 2 (25%) Sc.R 6 (75%) 10 (100%) Sc.St 2 (7%) 19 (61%) 3 (10%) 2 (6%) 5 (16%) PM 41 (100%) 25 (83%) PM 10 (24%) 0 (0%) 13 (32%) 10 (25%) 8 (19%) WSS 28 (80%) 14 (67%) WSS 2 (6%) 5 (14%) 8 (22%) 12 (33%) 9 (25%) WSR 42(100%) 22(85%) WSR 10 (24%) 5 (12%) 5 (12%) 9 (21%) 13 (31%) Soldering area (as in Fig. 9b) Sc.R 5 (50%) – 0 (0%) 3 (30%) 2 (20%) WSS soldering region demonstrates a better Pb–Zn PM 7 (23%) – 9(30%) 6(20%) 8(27%) correlation. WSS 3 (14%) – 2 (9%) 15 (72%) 1 (5%) The soldering region of the WSS group is in 71% of cases WSR 1 (4%) – 8 (31%) 3 (11%) 13 (54%) allocated to the correct group. Only six measurement points are better assigned to other groups (see Table 3). This group is n number of measurements best distinguished in terms of the solder composition (see Fig. 9b). However, the distinction between base and soldering is is important to know whether the silver comes from one or the most disturbed (as shown in Table 2 and Fig. 15a), which many different sources. It may be supposed that re-melting of is an effect of spilling of the solder over the surface (Wolters earlier artefacts took place in Europe since the Migration 1983). In Fig. 15, there are four protruding points in the group Period (400–800 AD). Therefore, one can expect more than with different compositions. These compositions are related to one value of individual isotopic ratios in one and the same two artefacts. Generally, in the WSS group, the soldering re- artefact. Due to this, destructive analytical techniques, such gion demonstrates slight Pb and Cu enrichments with a lower as TIMS or ICP-MS (e.g. Cattin et al. 2009; Ettler et al. oxidisation degree (Table 1,Figs. 5 and 6). 2015), may introduce a considerable error to the interpretation of results. This is because these techniques yield an average Lead isotopic characteristics of the provenance of raw result already in the course of sampling. In this paper, it is silver attempted at providing results of isotopic analyses taking into consideration changes of the so-called isotopic signature of One of the most important questions concerning the investi- the sample in the micro-scale. These changes may result from gated silver ornaments is the provenance of the raw material. It possible re-melting or heterogeneity of the raw material which Fig. 9 LDA showing the variability of a Ag, Cu, Bi, Au, Pb, Hg and O contents in the base surface of the archaeological types and b Ag, Cu, Bi, Au, Pb, Hg, Sn, Zn, Sb and O contents in the soldering area of the finds with granulations within archaeological types. Designations of the groups as in Table 1 6714 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 10 Scandinavian-type finds with wires from the Rajsków hoard presented in Fig. 3c as nos. 1 and 2 (Sc.R type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual finds from the group (zoom of Fig. 9b) was used. The isotopic analysis which is offered below was visible as a significant peak width, or the kernel function has divided into two areas—an analysis within technological several local maximums (see Fig. 16), one can suspect that the groups and a provenance analysis. In the latter case, geologi- silver was re-melted (Merkel 2016; Eniosova 2009;Eniosova cal data (as means) was taken from the available literature and Mitoyan 2011). Such a situation has been observed in all (Ettler et al. 2015;Merkelet al. 2013;Hatz et al. 1991). In the studied artefacts. both cases, all LA-ICP-MS results were taken into consider- Figure 17 and Table 4 (see also the Electronic supplement, ation for the artefacts. Furthermore, linear discriminant analy- 2. Linear Discriminant Analysis – Ornaments) offer an LDA sis was applied to search for differences between groups for lead isotope ratio distribution in four technological groups. 206 207 207 204 208 the following values: Pb /Pb ,Pb /Pb and Pb / The analysis demonstrates that the raw material is similar with 206 206 207 208 206 Pb , aswellasPb /Pb and Pb /Pb in the case of regard to its isotopic ratios in almost all the examined groups. the provenance analysis. Data obtained from the LDA confusion matrix demonstrates Moreover, a KDE model (Baxter 2003, 2016)proved use- that the highest lead isotope homogeneity can be seen in the ful, as it allows to create a continuous function describing the case of the West Slavic ornaments from Rajsków (WSR) probability distribution of the lead isotopic ratios being an (89% correct classifications). The percentage of correct clas- effect of the heterogeneity of metal in the examined artefacts. sifications is much lower for post-Moravian ornaments (mere- An example of such a model is presented in Fig. 16. ly 35%), while no correct classification was obtained for Having analysed lead isotopic ratios presented as Scandinavian ornaments and West Slavic ones from scatterplots and using the kernel density estimation of these Słuszków. ratios, one can draw conclusions about the provenance of The LDA (Fig. 18, see also the Electronic supplement,5. silver in the sample. If the values of lead isotopic ratios change Linear Discriminant Analysis—Provenance, Confusion ma- in one direction continuously from point to point, which is trix for the training sample) of the geological data Fig. 11 Round pendant (Fig. 3c, no. 2) from the Rajsków hoard, Scandinavian type—general view and SEM-SE images of the soldering region Archaeol Anthropol Sci (2019) 11:6705–6723 6715 Fig. 12 Post-Moravian–type finds with granulations from the Rajsków hoard presented in Fig. 3a as nos. 1–4(PM type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual artefacts from this group (zoom of Fig. 9b) demonstrates a strong similarity between ores. Out of 17 de- obtained. Not surprisingly, the metal in the artefacts was most- posits, a reasonable percentage of correct classifications was ly attributed to those deposits which were clearly different obtained in four cases only. The following deposits are clearly than others. different from others: Afghanistan, Freiberg (Germany) and Furthermore, these results demonstrate that the metal in a the Tatro-veporit unit (Slovakia)—100% of correct classifica- given artefact may be of different origin (see Electronic sup- tions. There is also a good isolation for Uzbekistan (76% of plement, 5. Linear Discriminant Analysis—Provenance, correct classifications). The assemblages of Rammelsberg Results for the prediction sample). This supports the assump- (Germany), Gammersham (Germany) and Neo-volcanic de- tion of re-cycling and re-melting of raw material from various posits are classified into the Tatro-veporit unit in 100% of sources. cases. The isotopic composition of samples from the Polish As it can be seen in Table 5 (see also the Electronic sup- deposits of Olkusz–Chrzanów–Pomorzany (marked as plement, 5. Linear Discriminant Analysis—Provenance, OlkChPom) and the Slovak deposit of Gemer is also similar Results for the prediction sample, and 6. Summaric results to the Slovak Tatro-veporit deposits. for provenance), the isotopic composition in individual groups This rather poor separation of deposits on the basis of Pb results from the fact of mixing of the raw material from isotopic ratios strongly influences the results of provenancing Central Asian (Afghanistan and Uzbekistan), German attempts. Results of 701 analyses on the discussed artefacts (Freiberg) and Polish ores. Interesting conclusions can be were processed by LDA, but in most cases (see Electronic drawn from the analysis of individual groups. In all Slavic supplement, 5. Linear Discriminant Analysis—Provenance, groups (that is, both West Slavic and post-Moravian), there Results for the prediction sample), no clear attribution to any is a preponderance of Freiberg silver over that from deposit was achieved. It was conservatively assumed that a Uzbekistan and Afghanistan (if considered separately). classification could be considered reliable when the prediction However, it seems that in total the Asian raw material still of probability was at least 70%. Thus, only in 250 cases (that played the most important role (Merkel 2016; Eniosova is, 36%), a more or less unambiguous classification was 2009). There are also some differences between groups of Fig. 13 Raspberry pendant (Fig. 3a, no. 2) from the Rajsków hoard, post-Moravian type—general view and SEM-SE images of the soldering region 6716 Archaeol Anthropol Sci (2019) 11:6705–6723 Fig. 14 West Slavic–type finds with granulations from the Rajsków hoard presented in Fig. 3b as nos. 1–6 (WSR type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual finds from the group (zoom of Fig. 9b) Slavic jewellery concerning the share of individual deposits. whose isotopic composition may be similar to those which What is most striking, however, is a very different proportion were included into the analysis. of metal from various sources in Scandinavian jewellery. The share of European deposits is 32%, while nearly 70% of metal seems to have come from Asian sources. Of course, these Discussion observations must be treated with care. First of all, the number of the examined artefacts was not very high, which may pose Jewelleries craft problems for the statistical representativeness of results. Furthermore, the aforementioned rather poor separation be- A significant part of the investigated jewellery from the tween individual deposits must be taken into consideration. Rajsków and Słuszków hoards is granulated. The results show Last, but not least, a problem of missing sources must be borne that these elements are permanently bonded to the substrate by in mind. That is, the LDA-based statistical processing of data the process based on the use of copper compounds (Kolářová will classify given observations only to those deposits which et al. 2014). The properties of solder based on Ag–Cu are are present in the assemblage. Silver which was used in the widely described in Nature (Ashkenazi et al. 2017). discussed artefacts could also come from other deposits, Intentional doping of silver with copper up to 2.6 wt% Fig. 15 West Slavic–type finds with granulations from the Słuszków hoard presented in Fig. 2 as nos. 1–5 (WSS type): a PCA results for the base surface and the soldering area and b LDA results for the soldering area of individual artefacts from the group (zoom of Fig. 9b) Archaeol Anthropol Sci (2019) 11:6705–6723 6717 207/206 208/206 Fig. 16 KDE calculated (surface plot of a scatterplot) for lead isotope ratios Pb and Pb for two artefacts from the Rajsków hoard as an example of re-melted samples (Ashkenazi et al. 2017) causes the melting point of Ag–Cu decoration is more problematic for filigree jewellery and gran- alloy to be lower than 961 °C for pure Ag (Tuah-Poku et al. ulation. When melted, the solder is not absorbed into the sur- 1988;Bastow 2013). From an old handbook (twelfth century face and forms a Bpuddle^ in which small decorative elements receipts of Theophilus Presbyter; Pliny 1929; Leyden Papyrus melt (Eilbracht 1999). This type of soldering has been identi- fied by Macháček et al. (2016) during their study of the Great X), two types of soldering—metallic and non-metallic (chemical)—are known. These were discussed in detail by Moravian jewellery and on the ornaments from the BLumbe Duczko (1985,p. 26–28). Garden^ cemetery at Prague Castle (Ottenwelter et al. 2014,p. Metallic solders known from the third century BC are mix- 283). In line with what was said above, the spilled granulation tures of two or three metals (Wolters 1978,p. 5; 1983,p. 62). (see Figs. 5 and 6) with higher contents of Pb and Cu (added While silver artefacts are soldered, the main component is Ag, as a joining Ag-based mixture) in the soldering area (Table 1) while other additions could be gold, brass or tin (Wolters is characteristic for the beads from Słuszków hoard. The beads 1978, 1983, p. 61ff). The obtained soldering effect is not ar- are remarkable for their relatively ungrouped granules, so the tistically convincing. The solder mixture covers the entire sur- assumption concerning the application of metallic soldering is face between the ornaments and the base surface (Carrol 1974, justified. The granules are tiny (300–400 μm) and the solder is p. 35; Kolářová et al. 2014). The use of metallic soldering is spilled over all the surface (see LDA: Table 3, Fig. 10a). Apart particularly advantageous when joining larger and more dura- from that, the shape between granules which are close to each ble jewellery items. However, using metal solder for other is fuzzy (see Fig. 5). The WSS group soldering area is strongly different from that in the remaining jewellery under study (Fig. 9b, Table 3). The remaining part of the examined jewellery with granu- lation and filigree from Rajsków (post-Moravian and West Slavic types) and Stojkowo (Scandinavian type) demonstrates traces of use of the non-metallic (chemical, bonding) solder- ing. Non-metallic solders consist either of mineral or artificial- ly produced copper compounds (Duczko 1985). Written sources described a few such substances: malachite (in antiq- uity called chrysocolla) and azurite, naturally occurring forms of basic copper carbonate; patina (i.e. a copper alloy resem- bling enamel covering old bronze artefacts—mostly copper carbonate, containing natural oxides and oxides of bronze additives—tin, lead, zinc, arsenic); verdigris, a mixture of ba- sic copper acetate and copper acetate pentahydrate, produced by the action of vinegar on copper; and Roman vitriol, cupric sulphate pentahydrate (Tamla 2016). In order to prepare a 206 207 207 204 208 206 Fig. 17 LDA showing Pb /Pb ,Pb /Pb and Pb /Pb diffusion agent, a copper compound is added to a mixture of variabilityinfour groupsofornaments 6718 Archaeol Anthropol Sci (2019) 11:6705–6723 Table 4 LDA confusion matrix From/to PM Sc.R WSR WSS Total % correct for the training sample. Data obtained for lead isotope ratios: n (%) 206 207 207 204 Pb /Pb ,Pb /Pb and 208 206 Pb /Pb in the jewelleries’ PM 58 (35%) 0 (0%) 107 (65%) 0 (0%) 165 (100%) 35 groups Sc.R 5 (7%) 0 (0%) 65 (93%) 0 (0%) 70 (100%) 0 WSR 32 (11%) 0 (0%) 266 (89%) 0 (0%) 298 (100%) 89 WSS 25 (15%) 0 (0%) 142 (85%) 0 (0%) 167 (100%) 0 n number of measurements Fig. 18 LDA showing Pb / 207 208 206 Pb and Pb /Pb variability for geological data (means) ob- tained from the literature Archaeol Anthropol Sci (2019) 11:6705–6723 6719 Table 5 Results of LDA ore Number of Prediction Prediction Prediction Prediction Prediction provenance classification for four analyses Freiberg Uzbekistan Afghanistan OlkuszChPom Gammersham jewelleries’ groups WSS 68 25 (37%) 18 (26%) 18 (26%) 6 (9%) 1 (1%) WSR 90 27 (30%) 31 (34%) 22 (24%) 10 (11%) 0 (0%) PM 73 28 (38%) 22 (30%) 14 (19%) 9 (12%) 0 (0%) Sc.R. 19 5 (26%) 10 (53%) 3 (16%) 1 (5%) 0 (0%) Total 250 85 (34%) 81 (32%) 57 (23%) 26 (10%) 1 (0%) an organic adhesive (e.g. gum tragacanth, gum acacia, fish- processing of gold, silver and copper. Burning charcoal main- glue) and water. Sometimes, such mixture is enriched by so- tains a temperature of 800 °C without an artificial air supply. called asem described by Leyden Papirus X (Demortier et al. The temperature increases to 1300 °C when air is supplied 1999). The nature of asem is unknown, but this term is used in through a single pair of bellows or a blow-pipe (tools primar- an old handbook with reference to a substance whose proper- ily required for minor soldering operations). If there is a con- ties are similar to precious metals (Berthelot 1889). With this tinuous blast from water-powered double bellows, the temper- solution, the decorative elements are fastened to the substrate, ature rises as high as 1650 °C (Untracht 1985). The other and the artefact is then heated (Wolters 1983). property of charcoal is the ability to create a reducing atmo- In reference to what was said above, the granulation and sphere, which protects the heated metal from oxygen in the air. wire-ornamented West Slavic (WSR), post-Moravian type This is important due to the presence of copper and other (PM) and Scandinavian finds from the Rajsków hoard show easily oxidising elements (such as zinc, tin, antimony in our Cu, Sn and Sb (see Table 1) enrichments with a higher oxida- cases) in solder alloys. When heated, those elements produce tion degree in the soldering area (see Figs. 7, 8, 11 and 13). oxides, which coat the surface of the artefacts, thus preventing ThecontentofCu(whichisameltingagent)isupto the completion of the soldering process, which is visible in 57.3 wt%. This gives a melting temperature over 779 °C (a Figs. 7, 8, 11 and 13. If charcoal fire is not sufficient to lower value occurs for 28.1 wt% Cu) (Ashkenazi et al. 2017). completely eliminate oxidisation, it is necessary to use a spe- The soldering regions of all three archaeological types from cial anti-oxidisation agent, called flux which coated all the the Rajsków hoard are similar (see Fig. 9b, Table 3). These are joints. The following substances could be used as flux: soda characterised by a good separation from the base surface (see (sodium bicarbonate NaHCO ), tartar (potassium bitartrate Tables 1 and 2). Furthermore, the bonding area with a higher KC H O ), alum (hydrated potassium aluminium sulphate 4 5 6 content of copper (Cu) is enriched in low-melting elements Kal(SO ) ∙12H O), potash (potassium carbonate K CO ) 4 2 2 2 3 (Sn, Sb, Zn; Baxter 2003). These were presumably intention- and the most important factor, that is, borax (sodium ally added to the alloy as asem in diffusion bonding or as part tetraborate Na B O ). All these substances are well docu- 2 4 7 of a Cu-based mixture. The oxidation of the soldering region mented in historical sources (Wolters 1978). is correlated with the presence of Cu and Zn in post- Furthermore, the presence of Zn and Sb in the joining mix- Moravian–type artefacts (see Fig. 12a), with the presence of ture can be associated with the use of such minerals as Sb, Cu and Sn in West Slavic finds (see Fig. 14a) and with the tetrahedrite ([Cu,Fe] Sb S )(Munoz etal. 2015), which is 12 4 13 enrichment in Sb and Sn in Scandinavian finds (see Fig. 15a). also a source of copper, and sphalerite (ZnS). The latter is Generally, the presence of the oxide structure in the joining often found with Ag-rich galena deposits (PbS) which were region, around the granules and wires, could result from the main source of silver in medieval Poland and Europe (Gale enough reducing atmosphere during the chemical soldering and Stos-Gale 2000; Chamberlain and Gale 1980). or could be an effect of improper heat treatment. If soldering Furthermore, antimony is associated with freibergite mineral is to be successful, it is essential for the metal surfaces to be [Ag (Cu Fe )Sb S ] which characterised Freiberg 6 4 2 4 13–x absolutely clean. This is because a series of thermal treatment (Germany) silver ores based on galena and sphalerite boards. reactions occurs during this process: at 100 °C, CuO is formed Antimony-rich deposits were also located in Poland in Lower from Cu compounds; at 600 °C, the reducing atmosphere is Silesia, e.g. in Dębowiny in the Beskidy Mountains between created by glue carbonising; and at 850 °C, Cu oxides are Srebrna Góra and Złoty Potok (Mączka and Stysz 2008). In reduced to Cu by CO (Duczko 1985, p. 25). Heating above the Early Middle Ages, silver was extracted in this region by a 900 °C causes the metallic copper to diffuse to the base sur- refining process called cupellation. The aforementioned min- face and to the alloy of ornaments (Wolters 1983, p. 57). erals which may have been a source of elements used to pro- Charcoal fuel was used as a temperature agent. It has certain duce soldering mixture could be added as asem part to resin properties which render it particularly suitable for soldering glue being a binder in non-metallic soldering. Moreover, with operations. It generates high temperatures necessary for the regard to the antimony content, we may assume that our 6720 Archaeol Anthropol Sci (2019) 11:6705–6723 ornaments were made of silver from cupellation directly asso- heat and then it dripped from the upper to the lower pot. The ciated with this element. An important thing in the cupellation resulting purified antimony sulphide is the modern commer- process is wasting of silver by evaporation and dissolution of cial “crude antimony” or “grey antimony” (Agricola 1912,p. silver in lead oxide (PbO) and later soaking into a cupel (al- 428). kaline—for example from animal bone bound with potash). In the case of mercury content in all studied artefacts, this An optimal amount of lead must be selected—and this already element was widely used in workshops working with precious shows the quality of the workshop (the same as the tempera- metals, especially gold. Vitruvius in his work “On architecture ture of the furnace, the amount of copper admixture and the ...” (Agricola 1912, p. 123) said: “Mercury is suitable for quality of the cupel itself). Also, a significant influence on many purposes. Without it, you can not gild either silver or silver wasting is exercised by the addition of antimony and bronze [...] mercury attracts all gold particles and connects tellurium which facilitate silver infiltration into the cupel. If with it.” Theophilus (1979) in his recipes recommends it, the addition of these elements actually took place in order to among others, as an additive for grinding gold or silver (five produce raw silver of the studied jewelleries, antimony would parts of mercury and six parts of silver), for obtaining the so- be present in the entire artefact and not only in the solder called sand (extracted from the sand mined on the banks of the region. Rhine) or as an alloy for casting tin vessels (one quarter pound From “De Re Metallica” of Agricola (the work is of a of tin for one pound of tin) and final polishing of these castings sixteenth century date, but it also discusses much earlier tech- (a mixture of dissolved tin chips in mercury). Therefore, the nologies), we learn that the stibium mineral (probably presence of gold and mercury in the results of research on the antimonite or other antimony minerals) was used, among ornaments is probably not intentional (traces after amalgam others, for the metallurgical process of recovering gold from gilding) but results from contamination, for example, with pyrite. Excepting reduction with silver, and separation with components of a solder or alloy intended for granulation. nitric acid and a method of reduction with lead and silver, followed by cupellation and parting with nitric acid is the third Assessing provenance method that can be isolated. Yet another method is the reduc- tion with lead or antimony, followed by cupellation. The use When analysing the origin of the raw material, it should be of sulphur or antimony sulphide would tend to part out a remembered that metal artefacts are not geological ores. The certain amount of silver and thus to obtain fairly pure bullion objects are created by a series of anthropogenic actions, such upon cupellation. as extraction of raw metal, re-cycling or alloying with other Silver was also parted from gold by means of stibium. The metal. These actions cause the artefact’s structure to be het- use of antimony sulphide to part silver from gold is based erogeneous in the micro-scale. This is reflected in the hetero- upon a greater affinity of silver than antimony to sulphur. geneity of the chemical composition–elemental and isotopic Thus, the silver, as in other processes, is converted into a character of the artefact (Liu et al. 2018). Therefore, the mea- sulphide and is absorbed in the regulus, while the metallic sured composition is merely a resultant of an average of the antimony alloys with the gold and settles on the bottom of composition. For this reason, the interpretation of the obtained the pot. This process has several advantages over the results may be burdened with an error, and it should be treated sulphurisation with crude sulphur; antimony is a more conve- as a subject for further verification. Furthermore, it could be nient vehicle of sulphur, for it saves the preliminary suggested that apart from Pb, other isotopic ratios may also be sulphurisation with its attendant difficulties of volatilisation of use, for example Cu and Ag (Desaulty et al. 2011). Quite of the sulphur; it also saves the granulation necessary in the promising results have recently been obtained in iron prove- former method; eventually, the treatment of the subsequent nance studies which employed Os isotopic signatures products is simpler. (Dillmann et al. 2017, with further reading). The process in this description can be divided into six op- Three phases of silver inflow are isolated for Poland in the erations: (a) sulphurisation of the silver by melting it with Early Middle Ages (tenth to twelfth century). In the first phase antimony sulphide; (b) separation of the gold “lump” which falls within the pre-state period (to the end of the tenth (massula) by jogging; (c) re-melting the regulus (mistura) century), there is a preponderance of oriental silver, chiefly three or four times for a recovery of further “lumps”; (d) re- Arab dirhams (Burâkov 1965, 1974; Bubnova 1963;Cowell melting of the “lump” four times, with further additions of and Lowick 1988;Dekówna 1971,p.496,487;Merkel 2016; antimony sulphide; (e) cupellation of the regulus in order to Eniosova 2009; Eniosova and Mitoyan 2011). For about recover the silver; and (f) cupellation of the antimony from the 250 years (since the eighth to the mid-tenth century), dirhams “lump” to recover the gold (Agricola 1912,p. 451). are the main component of hoards found in Poland. This The method described by Agricola for treating antimony changes in the second half of the tenth century, when sulphide was still in use in the twentieth century in the Harz, in Western European coins and then local issues commence to Bohemia and elsewhere. The stibnite was liquated out at a low prevail. This second wave of inflow (second half of the tenth Archaeol Anthropol Sci (2019) 11:6705–6723 6721 to late eleventh century) was related to a dominant role of However, at present, it is difficult to compare all previously coins which were coming to Poland from Western European published studies (Gójska et al. 2019)—most of the performed countries, chiefly from Germany, where enormous deposits of analyses were obtained by X-ray fluorescence spectrometry silver were discovered in the Harz in the Rammelsberg mine (XRF) or X-ray microanalysis spectrometry (EDX) on sur- in the third quarter of the tenth century (Jammer 1952,p. 62; faces (often corroded or contaminated), which may produce Suchodolski 1971, p. 22). The third phase is related to the use distorted results. This method is not accurate when examining of native silver and is well visible in finds since the rule of the raw material of the base surface, and the solder area is Bolesław Krzywousty (1107–1138). usually analysed along with the entire metal surface, which Due to the technological nature of the artefacts, i.e. their can distort the quantitative reading of elements (Ottenwelter heat treatment and a considerable blur of intentionally added et al. 2014). Nevertheless, studying ornaments by surface layers, there seems to be little point in attempting at techniques we obtain preliminary information about their interpreting the elemental composition in relation to the com- structure and chemical composition. In order to compare the position of individual geological deposits. More so, because raw material of alloys and silversmiths used in early medieval the discussed silver deposits are PbS and ZnS systems with Europe, it is necessary to continue systematic archaeometric similar additives. What is remarkable is the aforementioned research on similar ornaments, also with the use of invasive presence of Sb in the deposits from Freiberg and from Lower preparation (Kolářová et al. 2014) in order to establish a da- Silesia. The percentage share of individual elements in the tabase of comparative data. artefacts does not reflect the initial composition of the deposit, Studies on aesthetically and technologically advanced ar- which was first extracted from the ore. Then, the obtained raw tefacts from the Early Middle Ages reveal a completely new material was melted and intentional additives were added in aspect of the Slavic culture and are the basis for undertaking order to receive the desired technological parameters. international cooperation in methodological research on sim- The results of the Pb isotope ratio study provide grounds ilar finds from the Czech Republic and Scandinavia. for concluding that the silver used to produce the discussed Submitted results confirm a crucial role played by different early medieval artefacts comes from different sources and ores complementary analytical techniques, in particular SEM- (Table 5). This means that the investigated ornaments may EDX, LA-ICP-MS and also lead isotope ratios and statistical have been made of silver coming from various other artefacts methods in order to identify combined techniques used in and ores. The results of our investigations may suggest the silver ornaments and to establish the origin of the raw silver used for manufacturing the discussed jewellery chiefly material. originated from Asia (Uzbekistan and Afghanistan) or Funding information This work was has been carried out with the finan- Freiberg in Germany. cial support of the National Research Centre in Cracow, Poland (grant no. UMO-2013/09/B/HS3/03289). Conclusions Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// The obtained results provide detailed information about the creativecommons.org/licenses/by/4.0/), which permits unrestricted use, technological aspects of early medieval silver ornaments from distribution, and reproduction in any medium, provided you give Central and Eastern Europe and allow for an isolation of two appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. types of soldering. In the future, on the basis of studies on larger assemblages, it may be possible to propose a new and more relevant archaeological classification of these finds. This classification can be regarded as valid after a thorough exam- References ination and comparison of all the studies of ornaments from other West Slavic and Scandinavian territories. 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