Islamic glass in the Christian Kingdom of Alwa: Chemistry of shards from Soba, Nubia, Sudan

Received: 26 October 2022 Accepted: 26 April 2023 DOI: 10.1111/arcm.12878 ORIGINAL ARTICLE Islamic glass in the Christian Kingdom of Alwa: Chemistry of shards from Soba, Nubia, Sudan Joanna Then-Obłuska 1 1 Antiquity of Southeastern Europe Research Centre, University of Warsaw, Warsaw, Poland 2 Anthropology, Field Museum, Chicago, Illinois, USA Correspondence Joanna Then-Obłuska, Antiquity of Southeastern Europe Research Centre, University of Warsaw, Krakowskie Przedmie
scie 32, 00-927, Warsaw, Poland. Email: j.then-obluska@uw.edu.pl Funding information The Polish National Science Centre, Grant/ Award Number: UMO-2018/29/B/HS3/02533 | Laure Dussubieux 2 Abstract Excavations at Soba, the capital of Alwa, between 2019 and 2022 yielded more than 30 glass fragments in addition to a glass cosmetic bottle. An analysis of 30 glass samples has identified glass belonging to a number of compositional groups. The majority of fragments were made of plant ash-soda glass produced in the Middle East (Iran, Iraq) between the 9th and 10th centuries, and in the Eastern Mediterranean (Levant and Egypt) between the mid-10th and mid-12th centuries. Seven fragments were made of mineral–soda-lime glass produced in 9th-century Egypt and three highlead glasses find analogies in the 9th- to 11th-century glass. Archeological evidence, as well as textual sources, leave no doubt about Alwa’s intense transcultural connections. This article provides the first insight into the chemistry of glass shards from medieval Nubia, and the results of analysis contribute to evidence for long-distance contacts of Soba, the capital of one of the medieval kingdoms of Sahelian Africa. KEYWORDS Christian Nubia, elemental composition, glass, Islamic trade, LAICP-MS, medieval, Sudan INTRODUCTION Nubia, a region in Northeast Africa, stretched from the First Nile Cataract in the north, far beyond the confluence of the Blue and White Niles in the south (Figure 1a). During the Christian Period (c. 600–1400) there were three Nubian kingdoms: Nobadia was the northernmost with its This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2023 The Authors. Archaeometry published by John Wiley & Sons Ltd on behalf of University of Oxford. Archaeometry. 2023;1–14. wileyonlinelibrary.com/journal/arcm 1 THEN-OBŁUSKA and DUSSUBIEUX F I G U R E 1 Map showing locations of the sites mentioned in the text (a), excavated trenches (b), and samples (c) (by J. Ciesielska, Sz. Ma
slak, T. Michalik, J. Then-Obłuska). capital at Faras, Makuria was in the center in Upper Nubia with its capital at Old Dongola, and Alwa (Alodia) was upstream with its capital at Soba East on the Blue Nile. Soba was recognized as the capital of the largest Nubian kingdom. The foundation of a major urban settlement has been dated to the 5th–6th centuries CE, with its most intense development dating between the 6th and 11th centuries (e.g., Drzewiecki & Michalik, 2021). A prime time of Soba development appears to have been the 10th century, as documented by Ibn Selim el-Aswani, an Egyptian diplomat dispatched there (Vantini, 1975). He mentions gardens, fine buildings, large monasteries and churches, as well as a great suburb where many Muslims lived. Written sources indicate that Soba welcomed visitors from as far as the Mediterranean and Ethiopian highlands (Vantini, 1975). Monumental architecture, as well as large quantities of fine and unique artifacts excavated there, have given an insight into the city’s wealth and farreaching contacts (Drzewiecki, Ryndziewicz, Ciesielska, et al., 2020; Drzewiecki, Ryndziewicz, Michalik, et al., 2020; Drzewiecki et al., 2022; Shinnie, 1961; Welsby, 1998; Welsby, 2004; Welsby & Daniels, 1991). Among the imported items was glassware of types familiar from 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2 3 sites around the Arabian Peninsula and the western littoral of the Indian Ocean (Anderson & Welsby, 2004a, p. 229; Harden, 1961; Morrison, 1991; Ward, 1998; Welsby, 2004, p. 229). Past excavations at late antiquity and medieval Soba—that is, between the 5th and 14th centuries CE—reported good-quality table and perfume vessels, their fragments, as well as fragments of window panes and lamps (Harden, 1961; Morrison, 1991; Ward, 1998). Despite the presence of two amorphous, unworked blue glass lumps, suggesting glass objects may have been manufactured on site, no glass-working industry at Soba has been actually confirmed (Anderson & Welsby, 2004b, p. 235; Ward, 1998, pp. 83–84). Glass specimens found at the site are said to have been sourced from Iran, Iraq, and Egypt. However, the differences between the Iranian and Egyptian products are visually hard to distinguish (Morrison, 1991, p. 258; PinderWilson & Scanlon, 1987, p. 60). An attempt to solve the issue of identifying origins of the Soba glass analysis was undertaken to determine their chemical composition, the results of which are presented below. Recent excavations at Soba, between 2019 and 2022, of the interdisciplinary project “Soba—the heart of Alwa” directed by Mariusz Drzewiecki (Drzewiecki & Ryndziewicz, 2019; Drzewiecki et al., 2022; Drzewiecki, Ryndziewicz, Ciesielska, et al., 2020; Drzewiecki, Ryndziewicz, Michalik, et al., 2020; Drzewiecki & Michalik, 2021)—have uncovered only one cosmetic bottle and 32 glass vessel and window pane fragments. The present chemical compositional analysis of 30 glass fragments provides the first scientific evidence for the origin of glass vessels and window panes in the Christian capital on the Blue Nile and in Nubia in general. The study offers new data to the subject of the early Islamic glass trade in Northeast Africa between the 9th and the 12th centuries CE. SITE AND SAMPLES The remains of Soba are located on the right bank of the Blue Nile, approximately 15 km from downtown Khartoum. A larger part of the 275 ha area of the city has been, in the last 20– 30 years, subject to developments of urban infrastructure; for example, a new road has been constructed there (Drzewiecki & Ryndziewicz, 2019). However, thanks to the past excavations, approximately 1% of medieval Soba has been researched in detail (Drzewiecki & Ryndziewicz, 2019; Shinnie, 1961; Welsby, 1998; Welsby & Daniels, 1991). Although remains of medieval architecture are not visible on the surface, some previous surveys identified at least 17 mounds covered with red brick debris, and numerous mounds covered with gravel (Drzewiecki & Ryndziewicz, 2019). Recent excavations, designed to reconstruct the spatial organization of the city, uncovered residual and post-occupational burial deposits in some trenches in areas OS, SH, CW, CV, GN, and CS. Architectural remains, mud-brick and wooden structures, were uncovered. Burials were cut into the topmost layers of the trench 1/OS. In general, excavations yielded a large amount of pottery as well as faunal remains, stone tools, a few metal objects, beads, and some glass fragments (e.g., Drzewiecki & Ryndziewicz, 2019; Drzewiecki, Ryndziewicz, Ciesielska, et al., 2020; Drzewiecki, Ryndziewicz, Michalik, et al., 2020; Drzewiecki et al., 2022). The glass sample assemblage consists of 30 glass fragments, most of which have been excavated in residual deposits in six trenches: 1/OS, 2/OS, 1/CW, 1/SH, 1/GN, and 2/GN (Figure 1b). Nine samples were found in trench 1/OS (deposits 1, 6, 8, 9, 12, 19) (Figure 1c: Sv.01–03, 05, 6A–B, 07, 09–10), one fragment in trench 2/OS (deposit 4), and two fragments in trench 1/CW (feature 30, deposit 8) (Figure 1c: Sv.08 and Sv.18–19, respectively). Additionally, 11 fragments have been recorded from trench 1/SH (feature 26, deposits 1, 3, 4, 5, 9, 10) (Figure 1c: Sv.11A–D, 12–13, 14A–B, 15–17). Trench 1/GN (deposit 1) provided two fragments and trench 2/GN (deposits 5, 20) three fragments (Figure 1c: Sv.20A–B and Sv.22–23A–B, respectively). Another two fragments were surface finds (Figure 1c: Sv.04, 21). All samples were 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ISLAMIC GLASS IN THE CHRISTIAN KINGDOM OF ALWA: CHEMISTRY OF SHARDS FROM SOBA, NUBIA, SUDAN THEN-OBŁUSKA and DUSSUBIEUX nondiagnostic pieces, less than 4 cm in width, and most of them were covered with a thick layer of whitish or blackish patina. Where diaphaneity and color could be discerned, the fragments were usually of transparent and translucent glass: colorless, colorless with greenish and yellow tinge, green, and blue. All samples in this study are presented in Data S1 (Supporting Information), arranged according to trench, color, thickness, inventory number, and glass type. METHOD Elemental analyses were carried out at the Field Museum of Natural History in Chicago, IL, USA, by inductively coupled plasma mass spectrometry (ICP-MS) with a Thermo ICAP Q instrument connected to an electrospray ionization laser (Elemental Scientific Lasers NW213) for direct introduction of solid samples. The parameters of the ICP-MS (argon flow, radio-frequency power, torch position, lenses, mirror and detector voltages) were optimized using the National Institute of Standards and Technology (NIST) standard reference material 612 to ensure a stable signal with a maximum intensity over the full range of masses of the elements, and to keep the oxides and doubleionized species formation below 1–2%. For better sensitivity, helium was used as a gas carrier in the laser. In order to determine elements with concentrations in the range of parts per million and below, while leaving a trace on the surface of the sample invisible to the naked eye, the single-point analysis mode was used with a laser beam diameter of 55 μm, operating at 40% of the laser energy (0.1 mJ) and at a pulse frequency of 20 Hz. A pre-ablation time of 20 s was set, first, to eliminate the transient part of the signal and, second, to make sure that a possible surface contamination or corrosion would not affect the results of the analysis. For each glass sample, an average of four measurements corrected from the blank was considered for the calculation of concentrations. To improve the reproducibility of measurements, an internal standard is required to correct possible instrumental drifts or changes in ablation efficiency. The element chosen as an internal standard has to be present in a relatively high concentration so that its measurement is as accurate as possible. In order to obtain absolute concentrations for the analyzed elements, the concentration of the internal standard must be known. In the said analysis 29Si isotope was used for internal standardization. Concentrations of major elements, including silica, are calculated assuming that the sum of their concentrations in weight percentage in glass equals 100% (Gratuze, 2016). Fully quantitative analyses are possible with the use of external standards. To prevent matrix effects, the composition of standards must be as close as possible to that of the samples. Different standards are used to measure major, minor and trace elements. SRM 610 is a sodalime–silica glass doped with trace elements in the range of 500 ppm. Certified values are available for a very limited number of elements. Concentrations as in Pearce et al. (1997) are used for other elements. The second series of standards were manufactured by Corning glasses B and D, which are glasses that match the compositions of ancient glass (Brill, 1999, vol. 2, p. 544). All standards are measured with each batch of samples, which consists generally of 10 glass objects. Accuracy and precision of our measurements are assessed through the measurement of Corning glass A throughout the day with each batch of samples (see Data S2, “Corning A glass results”, Supporting Information). Accuracy is the relative deviation between the accepted concentrations (Vicenzi et al., 2002) and the average concentrations measured by laser ablation– ICP-MS for a given sample. It is generally better than 10%. It is important to note that the homogeneity of Corning A has never been tested (in general, and more particularly for the trace elements) and it is possible that some heterogeneity of the glass accounts for higher relative 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 4 5 standard deviation (RSD) for some elements. Reproducibility is a way to assess that our results are consistent over time. Reproducibility can be calculated as the RSD obtained from multiple measurements carried out over several days to several months on a same sample (here again, we used Corning glass A). For the Soba glass samples, measurements were carried out within a single day and the RSD were usually lower than 10%. The very low concentrations of the rare earth elements in Corning glass A, close to the limits of detection for these elements, accounts certainly for higher RSD. More details are available in Dussubieux (2022). RESULTS AND DISCUSSION Results of the compositional analyses of 30 glass fragments are given in the Supporting Information in Data S3. Soda-lime glasses, with seven samples made of mineral–soda-lime glass (m-Na-Ca), and 20 samples made from plant ash–soda-lime–silica glass (v-Na-Ca) make up the largest group (Figure 2). High-lead glass (Pb-Si) is represented by three fragments. Mineral–soda-lime glass Soda-lime glass with low MgO and K2O (<1.5%) levels, pointing to the use of a mineral–soda flux usually in the form of natron from Wadi el Natrun in Egypt, has been attested for seven fragments (Sv.02, 6A, 10, 19, 14A–B, 17). Glass of this type, common in the Southern and Eastern Mediterranean, was also known in Egypt between the 10th century BCE and mid-9th century CE when a shift from natron to plant ash used in glass making took place (e.g., Phelps et al., 2016; Shortland et al. 2006). Egyptian primary glass can be distinguished from Levantine glass based on TiO2/Al2O3 and Al2O3/SiO2, and Y2O3/ZrO2, and CeO2/ZrO2 ratios: the Egyptian glass features higher TiO2, and lower Y2O3/ZrO2 and CeO2/ZrO2 ratios (<0.08 and <0.18, respectively), compared to glasses from the Levant (>0.1 and >0.24) (Freestone, 2020a, fig. 22.1; Schibille et al., 2018; Figure 3b,c). A comprehensive chronological specification of the Levantine and Egyptian F I G U R E 2 Chemical variability of the investigated fragments based on MgO and K2O determination (data given as wt%). See also Supporting Information, Data S3. 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ISLAMIC GLASS IN THE CHRISTIAN KINGDOM OF ALWA: CHEMISTRY OF SHARDS FROM SOBA, NUBIA, SUDAN FIGURE 3 6 Legend on next page. THEN-OBŁUSKA and DUSSUBIEUX 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 7 F I G U R E 3 (a) Ratios of Y2O3/ZrO2 and CeO2/ZrO2 showing Egyptian origin of mineral–soda glass from Soba (Schibille et al., 2019, data S—Egypt; Phelps et al., 2016, appendix a - Levant). (b) Ratios of Al2O3/SiO2 and TiO2/ Al2O3 showing Egyptian origin of mineral–soda glass from Soba (Schibille et al., 2019, data S—Egypt; Phelps et al., 2016, appendix a - Levant). (c) Biplot of Na2O (wt%) and CaO (wt%) showing Egyptian (E2 > 815 CE) origin of mineral–soda glass from Soba (Schibille et al., 2019). See also Supporting Information, Data S3. natron glass has been accomplished based on the composition of Islamic glass weights (Schibille et al., 2019; Schibille, 2021, tab. 3). The low ratios of CeO2/ZrO2 (0.07 and 0.08) and Y2O3/ZrO2 (0.4) in the m-Na-Ca samples from Soba point to the Egyptian origin of the glass (e.g., Schibille et al., 2018; Figure 3b; ThenObłuska & Dussubieux, 2023a; Figure 3a). Ratios of TiO2/Al2O3 (0.09–0.10) to Al2O3/SiO2 (0.034–0.043) plot close to the results given for natron glass produced in the 8th–9th century Egypt (Freestone, 2020a, fig. 22.1; Schibille et al., 2019, 2021) (Figure 3b). With low levels of Na2O (12–13.9%) and high levels of CaO (9.0–9.9%) the m-Na-Ca glass from Soba fits well with “Egypt 2” glass group dated between 815 and 870 CE as given for early Islamic natron-type glass groups from Egypt (Schibille, 2021, tab. 2; Schibille et al., 2019, tab. S1; Figure 3c). Plant ash–soda glass Twenty soda-rich samples, with relatively high levels of MgO and K2O (>1.5%), were made from soda plant (vegetal) ash, labeled as v-Na-Ca glass, and produced since the middle of the second millennium BCE in Egypt and Mesopotamia (e.g., Shortland et al. 2007). Glass of this type has been attested for regions east of the Euphrates, where both Sasanian and Islamic glassmakers produced it between the 3rd and 17th century CE (e.g., Henderson et al., 2016—Raqqa, Syria, 8th–11th centuries; Mirti et al., 2008, 2009—Veh Ardasir, Iraq, 3rd–7th century CE, Sasanian glass; Henderson et al., 2016—Nishapur, Iran, 9th–10th century; Phelps, 2016; Schibille et al., 2018—Samarra, 9th century). Levantine earliest finds of the Islamic soda-ash glass can be dated to as early as the end of the 8th century, while the Egyptian samples come from the 10th century at the earliest (Gratuze & Barrandon, 1990; Henderson et al., 2016; Phelps, 2016, 2018). A number of glass subgroups, supposedly of various provenance, have been identified with the use of concentrations of certain elements. The Middle East/ “Mesopotamian” glass (likely produced in Iran and Iraq) is characterized by higher MgO/CaO ratios when compared to the Eastern Mediterranean (Egypt, Levant and South Syria) glass, suggesting different sources of soda plant ash used. Additionally, differences in some trace elements, such as Cr, generally lower in the Eastern Mediterranean glass, seem to indicate the use of different sand sources (Henderson et al., 2016; McIntosh et al., 2020; Phelps, 2016; Schibille et al., 2018, 2022). Recent studies have provided further chronological grouping of early Islamic plant ash soda glass (Schibille, 2021, tab. 7; Schibille et al., 2018, 2019). For the “Mesopotamian” glass group, using the concentrations of Al2O3, further groupings appear with a Type 1 glass with higher alumina concentrations compared to a Type 2 glass (Phelps, 2016; Schibille et al., 2022). Two of these subgroups could be identified among Soba samples: the Middle East/“Mesopotamian” (Iran, Iraq) and the Eastern Mediterranean (Egypt and Levant) (Figure 4a). v-Na-Ca Middle East/“Mesopotamian” Ten samples (Sv.01, 05, 06B, 08, 18, 11B–D, 20A, 23B) have higher MgO/CaO ratios and therefore plot well with the “Mesopotamian” subgroup (see Figure 4a). Their identification is 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ISLAMIC GLASS IN THE CHRISTIAN KINGDOM OF ALWA: CHEMISTRY OF SHARDS FROM SOBA, NUBIA, SUDAN FIGURE 4 8 Legend on next page. THEN-OBŁUSKA and DUSSUBIEUX 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 9 F I G U R E 4 (a) Biplot of Al2O3 (wt%) and MgO/CaO showing results for the v-Na-Ca glass from Soba, the “Mesopotamian” glass from Samarra 1 & 2 (Schibille et al., 2018), Iranian glass from Raqqa, 9th century (Henderson et al., 2016, type 4) and Nishapur, 9th–10th century (Henderson et al., 2016), and Eastern Mediterranean glass from Raqqa (Henderson et al., 2016, type 1) within range borders according to Phelps et al. (2016). (b) Biplot of Fe2O3 (wt%) and Cr (ppm) confirming the Iranian and Eastern Mediterranean sources of plant ash–soda glass for glass fragments found in Soba. (c) Ratios of Cr/La to Ti/Zr confirming different origins for the two types of plant ash–soda glass found in Soba. See also Supporting Information, Data S3. confirmed by their Cr and Fe2O3 concentrations, with Cr concentrations generally higher for a given iron concentration in this group compared to the Eastern Mediterranean v-Na-Ca glass group, and the Cr/La ratio is also higher in the “Mesopotamian” v-Na-Ca glass when compared to the Eastern Mediterranean one (Henderson et al., 2016; McIntosh et al., 2020; Schibille et al., 2018, fig. 11; Figure 4b,c). This glass subgroup can be further divided, also using the Al2O3 concentrations, into two types (see Figure 4a): “Mesopotamia” Type 1 (higher Al2O3 concentrations) with samples from Nishapur (9th century) and Raqqa (type 4; 9th century), and “Mesopotamia” Type 2 (lower Al2O3 concentrations) with samples from Samarra (mid-9th century); the latter type is further divided into Samarra 1 and 2 (Henderson et al., 2016, 2004; Phelps, 2016; Schibille et al., 2018, fig. 6). Nine samples from Soba (Sv.01, 05, 06B, 18, 11B–D, 20A, 23B) in the “Mesopotamian” subgroup with Al2O3 > 1.8%, fits the “Mesopotamian” Type 1 glass that was produced in Iran in the 9th century (Henderson et al., 2016, 2004; Phelps, 2016; Schibille et al., 2018, fig. 6; Schibille et al., 2022; see Figure 4a). One sample (Sv.08) is in fact a borderline case between “Mesopotamian” Type 1 and 2 (see Figure 4a) and its composition matches results for some major and minor elements in both Nishapur 1a and Samarra 1 groups (Schibille, 2021, tab. 7). However, its low level of Al2O3 (1.2%), and the concentrations of trace elements—TiO2 (0.03%), Ce (6 ppm), Cr (16 ppm), Sr (281 ppm), and Li (20 ppm)—match better the Samarra 1 subgroup in the “Mesopotamian” Type 2 glass (Schibille, 2021, tab. 7). Although compositions of two samples (Sv.16, 21) plot with results for Eastern Mediterranean glass (see Figure 4a), concentrations of Cr and Fe2O3 and Ti/Zr to Cr/La ratios contradict the group attribution as determined with the use of the MgO/CaO ratio and their alumina concentrations, suggesting a “Mesopotamian” origin for the two samples (see Figure 4b,c). Those two samples have therefore a sand that would be similar to that of the “Mesopotamian” v-NaCa glass but their flux resembling that of the Eastern Mediterranean v-Na-Ca glass. They could belong to a separate group or result from a mix of different glass types. Sv.21 is a dark-blue shard colored with Co (645 ppm), Zn (199 ppm), and Ni (136 ppm). Although cobalt glass is well recognized from Ramla (Phelps, 2018) and as Eastern Mediterranean imports from Samarra (Schibille et al., 2018), concentrations of the mentioned elements differ significantly from the ones in the Soba sample. v-Na-Ca Eastern Mediterranean Compositions of eight samples (Sv.03, 07, 11A, 12, 13, 20B, 22, 23A) have lower MgO/CaO ratios and therefore plot well with the Eastern Mediterranean glass (see Figure 4a). Their identification is confirmed by their Cr and Fe2O3 concentrations, with Cr concentrations generally lower for a given iron concentration in this group compared to the “Mesopotamian” v-Na-Ca glass group, and the Cr/La ratio is also lower in the Eastern Mediterranean v-Na-Ca glass when compared to the “Mesopotamian” one (Henderson et al., 2016; McIntosh et al., 2020; Schibille et al., 2018, fig. 11; see Figure 4b,c). Results obtained for Islamic glass weights (Schibille, 2021, tab. 3; Schibille et al., 2019), including TiO2/Al2O3 ratio of as well as concentrations of Zr and TiO2, useful in distinguishing 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ISLAMIC GLASS IN THE CHRISTIAN KINGDOM OF ALWA: CHEMISTRY OF SHARDS FROM SOBA, NUBIA, SUDAN THEN-OBŁUSKA and DUSSUBIEUX F I G U R E 5 (a) Ratios of MgO (wt%) to TiO2/Al2O3 showing Egyptian and Levantine origin of the Eastern Mediterranean glass from Soba (Schibille et al., 2019). (b) Biplot of TiO2 (wt%) and Zr (ppm) confirming Egyptian and Levantine origin of some plant ash–soda glass from Soba (Schibille et al., 2019). See also Supporting Information, Data S3. 10 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 11 Egyptian and Levantine glass, allow greater accuracy in provenance specifications (Figure 5a,b). Five v-Na-Ca samples from Soba (Sv.11A, 12, 20B, 22, 23A) in the Eastern Mediterranean group have low ratios of TiO2/Al2O3 (<0.05) and low concentrations of Zr (<42 ppm), matching the results for plant ash Levantine glass dated between the mid-10th and first quarter of the 12th century (Schibille et al., 2019; Schibille, 2021, tab. 3; Figure 5a,b). With its low concentration of ZrO2 (between 48 and 69 ppm) the Levantine glass from Soba would fit best glass from Tyre, Lebanon, dated to the 10th–11th century (Phelps, 2018, tab. 11.6). Although glass in Sv.07 has a relatively high level of Zr (51 ppm), which would suggest its Egyptian origin, high levels of MgO (3.2%) and a low level of TiO2 (0.09%) point to its Levantine provenance (Schibille, 2021, tab. 3; Figure 5a,b). With levels of Al2O3 (2.3, 2.0%), TiO2 (0.13, 0.11 ppm), and Zr (51, 49 ppm) two Soba vNa-Ca samples (Sv.03, 13) match best the results for Egyptian “plant ash E1” dated between the mid-10th and mid-12th centuries (Schibille, 2021, tab. 3; Schibille et al., 2019; Figure 5a,b). Pb-Si Three samples were made of high-lead glass. Two of them feature very high levels of PbO (>60%) (Sv.04, 15) and concentrations of alkali or alkali earth-based oxides below 1%, while the third sample (Sv.09) has a lower concentration of lead (44.6%), and higher concentrations of soda (4.6%) and lime (3.6%). The three samples are transparent green and contain significant concentrations of copper (0.7–0.8%) that produce a green glass when lead is present. Emerald high-lead compositions are found in different points of the Islamic word in contexts dating from the 9th to the 11th century CE. The high-lead soda samples are close in composition of specimens: from Aqaba in Jordan, dating from the Fatimid period (Meyer & Dussubieux, 2022), from Heshbon, 9th century CE, also in Jordan (Brill, 1999, vol. 2, p. 204), from the shipwreck of the Serçe Limani, 11th century CE (Brill, 1999, vol. 2, pp. 182–183) and from Sabra-Al-Mansuriya, Tunisia, mid-10th to mid-11th century CE (Freestone, 2020b). The presence of compositions slightly different among the high-lead–green glass group thus implies the existence of different workshops that may have produced them, although their location remains unknown (Brill, 1999, vol. 2, pp. 182–183; Freestone, 2020b; Wypyski, 2015; Meyer & Dussubieux, 2022). CONCLUSIONS While some objects from Soba were made of m-Na-Ca glass and a few samples were of highlead glass, it is fragments of v-Na-Ca glass that dominated the shard assemblage. The Soba m-Na-Ca glass was made in the 9th-century Egypt. The v-Na-Ca glass fragments originate from a variety of sources, and domination of v-Na-Ca “Mesopotamian” Type 1, produced in the 9th–10th century, would suggest strong connections of Soba with the Middle East region (Iran). Interestingly, glass made of the “Mesopotamian” Type 2/Samarra, known from the 9th-century Iraq, is represented by only one shard. The links with the mid-10th- to mid-12th-century Eastern Mediterranean region are mainly evidenced by the presence of the Levantine v-Na-Ca glass and only a few fragments of Egyptian v-Na-Ca glass. Finally, the high-lead glass from Soba has not been identified with any specific place of origin, although its dating, between the 9th and 11th century, is consistent with the dating of the other glass types found at the site. The results for shards from the medieval Nubian site of Soba are partially consistent with the early Islamic bead glass evidence as presented for other parts of Africa around the 10th century, including the Middle Nile region (e.g., Then-Obłuska & Dussubieux, 2023a; Wood, 2020). 14754754, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/arcm.12878 by Cochrane Poland, Wiley Online Library on [17/05/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ISLAMIC GLASS IN THE CHRISTIAN KINGDOM OF ALWA: CHEMISTRY OF SHARDS FROM SOBA, NUBIA, SUDAN Nevertheless, studies of bead glass from Soba bring more comprehensive evidence in tracing overseas trade connections of the medieval capital in Sahelian Africa (Then-Obłuska & Dussubieux, 2023b). A C K NO W L E D G E M E N T S The study is a part of the project “Soba—the heart of Alwa” funded by the Polish National Science Centre (grant no. UMO-2018/29/B/HS3/02533). We want to thank Dr Ghalia Garelnabi Abdelrahman (acting General Director of the National Corporation for Antiquities and Museums, NCAM) for permission to export and work on the samples. 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