The compositions of the glass beads, including 56 major, minor, and trace elements, were obtained using LA-ICP-MS at the Elemental Analysis Facility at the Field Museum. More details on the instrumentation and protocol are in Then-Obłuska and Dussubieux (2021), and ESM 2 presents major, minor, and trace element compositions of Corning Reference Glass B and D. Seventy-six glass beads, pendants, and chunks were analyzed. Different colors of the bichrome and polychrome beads were measured individually, and some measurements had to be repeated because, in some cases, the color meant to be targeted had been missed, and another one was measured instead. These resulted in 112 compositions (ESM 3). Soda is the main alkali in all glass samples, and four main glass types were identified based on the content of MgO and Al2O3 (Fig. 3). Soda-lime glasses form the most numerous group with eight samples made of plant ash-soda-lime glass (v-Na-Ca) and 84 samples made of a mineral soda-lime glass (m-Na-Ca). Four samples feature mineral- or plant ash-soda composition (m/v-Na-Ca), and 16 samples are mineral soda-high alumina (m-Na-Al) (Table 1).
Fig. 3Chemical variability of the investigated beads: low-alumina soda-lime glass, high-alumina glass, and plant-ash soda-lime glass based on MgO and Al2O3 determination (data are given as wt.%)
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Table 1 Glass composition groups for analyzed beads from Lower Nubian sites, arranged by periodFull size table
Eight samples made from soda-rich glass have low alumina (Al2O3 < 2%) and high magnesia (MgO > 3%) concentrations, indicating the use of plant-ash soda as a flux. Lime (CaO) concentrations range 3.5–8.0%. Plant-ash soda-lime-silica glass (v-Na-Ca) is the earliest known glass type. It was produced in Egypt (e.g., Rehren & Pusch, 2005; Smirniou & Rehren, 2011; Tite & Shortland, 2003) and Mesopotamia (e.g., Shortland et al., 2018) as early as the middle of the second millennium BC. Later, v-Na-Ca glass was made by the Sasanians. This was followed by Islamic glass-makers in a region east of the Euphrates from the third century BC to about the seventeenth century AD, and by Islamic glass-makers in the East Mediterranean region, Egypt, and the Levant, starting from the mid-ninth century AD (Brill, 2005; Henderson et al., 2016; Mirti et al., 2008, 2009; Phelps, 2016). Based on different levels of MgO and trace constituents such as Ti, Zr, Cr, and La, two subtypes of plant ash-soda glass are distinguished in the OINE assemblage: New Kingdom (v-Na-Ca NK) and Medieval (v-Na-Ca OINE73) (Fig. 4A).
Fig. 4A A biplot of chromium/lanthanum versus 1, 000 × zirconium/titanium in OINE v-Na-Ca glass in frames for late Bronze Age glasses from Egypt (Amarna and Malkata) and Mesopotamia (Tell Brak and Nuzi) (based on Shortland et al., 2007); B Biplot of Al2O3 and MgO/CaO showing results for v-Na-Ca glass OINE73, and “Mesopotamian” glass from Samarra 1 & 2, mid-ninth century AD (Schibille et al., 2018), Raqqa, ninth century AD (Henderson et al., 2016), Nishapur, ninth and tenth century AD (Henderson et al., 2016), and Veh Ardasir, AD 300-700 (Mirti et al., 2008, 2009), within range borders, according to Phelps (2016)
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A pendant of light blue wound glass decorated with a white spiral trail (OINE65Bl, W), found in Nobadian grave R 119 at Qustul and thought to be Meroitic in date (Williams, 1991, p. 146), is part of a v-Na-Ca sub-group. It has low levels of Rb (about 11 ppm) and Li (about 5 ppm). These chemical attributes exclude glass affiliation with contemporary v-Na-Ca Sasanian glass, featuring higher levels of both elements (e.g., Mirti et al., 2009; Then-Obłuska & Dussubieux, 2016). The two-colored glasses used to make this pendant have trace element levels indicating a Late Bronze Age date. Soda plant ash glass was produced since the middle of the second millennium in Egypt and Mesopotamia, and both production areas can be distinguished by plotting Zr/Ti and Cr/La ratios. A high ratio of 1000*Zr/Ti > 40 and a low ratio of Cr/La < 4 suggest Egyptian provenance of the glass, while the ratios of 1000*Zr/Ti < 60 and Cr/La > 4 indicate Mesopotamian glass (Shortland et al., 2007). Comparison of the two ratios in OINE65 with those in Late Bronze Age glasses from Egypt and Mesopotamia (based on Shortland et al., 2007; Henderson, 2013, Fig. 6.10) reveals similarities with the Egyptian data (Amarna and Malkata) (Fig. 4A).
Undoubtedly, the blue glass (OINE65B) owes its color to the presence of CuO (2.5%), although a contribution of Fe2O3 (0.5%) cannot be excluded. Traces of tin, SnO2 (0.09%), Co (61 ppm), and Ni (62 ppm) might have been brought in accidentally by the copper. All the elements occur in proportions resembling the scores for the “Cu blue” glass from Amarna and Malkata (Shortland & Eremin, 2006, Table 1). The white glass (OINE 65 W) has CaO at a level of 6.5% and a very high level of Sb2O5 (5.1%) and, like the New Kingdom v-Na-Ca glass from Amarna and Malkata, was decorated with calcium antimonate (Shortland & Eremin, 2006, p. 591, Table 1). Similar proportions of CaO in the blue and the white glass prompt the conclusion that the latter color was obtained solely by adding antimony to the colorless glass. Antimony precipitated with the calcium in the glass made with soda plant ashes, and calcium antimonate was obtained in this way (Shortland, 2002).
A higher level of Al2O3 and Sb2O5 in the white glass (OINE65W) along with traces of cobalt in copper blue glass (OINE65B) would exclude its affiliation with later New Kingdom glass from Lisht, dated to the end of the second millennium (Shortland & Eremin, 2006, p. 596–597, Table 2). Furthermore, the presence of traces of SnO2 in OINE65B would also exclude its affiliation with early New Kingdom blue glass dated to the fifteenth century BC (Shortland & Eremin, 2006, p. 596–597, Table 2). The OINE65 affiliation with the Amarna and Malkata sites, assumed glass-making centers in the fourteenth century BC (Shortland & Eremin, 2006), makes this bead stand out from the Nobadian tomb collection. The bead may have been moved from one of the New Kingdom tombs at Qustul (Then-Obłuska, forthcoming; Williams, 1992). Bichrome pendants with a similar trail added spirally are dated to the New Kingdom period (Spaer, 2001, cats. 72–74). Another bead, OINE62, found in a 25th Dynasty grave, features higher K2O (1.3%) and high MgO (2.8%), and its translucent purple wound glass has 0.8% MnO and 0.7% Fe2O3. Although the New Kingdom glass usually features more elevated magnesium and potassium (Shortland & Eremin, 2006), OINE62 still seems to fit this glass group since it typologically resembles other New Kingdom beads (Then-Obłuska in press: cat. 324.1, from Qustul R 94 dated to New Kingdom Post-Amarna period; Metropolitan Museum of Arts, New York, MET 11.215.661, from Malqata, Palace of Amenhotep III, ca. 1390–1353 BC). Also, comparing its Cr/La and 1000*Zr/Ti ratios with records for Egyptian and Mesopotamian glass makes its attribution to New Kingdom Egyptian glass fairly apparent (Fig. 4A).
Other v-Na-Ca compositions belong to a polychrome bead fragment, OINE73A-E, found in a Nobadian house (fourth–sixth centuries AD), thus implying the v-Na-Ca OINE73 glass could have been produced during the Sasanian period. To date, the OINE73A-E data for the various colored glass fragments were placed in a MgO/CaO vs. Al2O3 graph. The result demonstrated a distinction between the soda plant ash glass of Eastern Mediterranean provenance (Syria, Egypt, and Palestine/Levant) and the soda plant ash from the Mesopotamian region (northern Syria, Iran, and Iraq), dated between the eighth and tenth centuries AD (McIntosh et al., 2020; Phelps, 2016; Schibille et al., 2019). Further, two groups have been distinguished in the Mesopotamian glass: Mesopotamian Type 1 with samples from Veh Ardasir (third through seventh centuries AD) and Raqqa (type 4; ninth century AD), and Mesopotamian Type 2 with samples from Samarra (Schibille et al., 2018, Fig. 6). The results for OINE73, with Al2O3 (about < 1.5%), fit the Mesopotamian Type 2 (Phelps, 2016; Schibille et al., 2018; Fig. 6), particularly the Samarra 2 sub-group (Fig. 4B).
Analyses of (de)colorants and opacifiers in OINE73 are compatible with an Islamic glass-period affiliation. All glasses (yellow, black, red, and colorless) contain some concentrations of SnO2 and PbO (> 2%). The white (PbO2 and SnO2 = 1.6%) and yellow (PbO = 8.7%, SnO2 = 1.05%) colors were opacified with tin oxide and lead stannate, accordingly. The yellow color has some traces of antimonate (0.04%). Although, after the fourth century AD, tin, instead of antimonate, was used as an opacifier (Tite et al., 2008), occasional use of antimonate and arsenic was recorded for Merovingian- and Islamic-period yellow and greenish-yellow glass (Neri et al., 2019). With all the above in mind, the OINE73 fragment may be assumed to be a Medieval intrusion in the context of the Serra East Nobadian household rather than a Sasanian production. In fact, OINE73A-E is the fragment of a bead made of mosaic glass with a so-called checkerboard pattern already known in the Hellenistic period, and its production continued through Medieval times (e.g., Spaer, 2001, p. 120). The glass might have arrived through the Red Sea ports of Aidhab (used as a port at least from the time of the Fatimid conquest of Egypt in AD 969) and Suakin, some 230 miles south of ʿAidhab, founded in the ninth century.
Most analyzed OINE samples (n = 84), featuring low alumina (< 3%), also have low magnesia (< 1.5%) concentrations, indicating the use of mineral soda as flux. Soda-lime glass, using mineral soda as a flux — usually in the form of natron from Wadi el Natrun in Egypt — was manufactured in Egypt and the Syro-Palestinian region for two millennia, between the tenth century BC and mid-ninth century AD (e.g., Phelps et al., 2016; Shortland et al., 2006). Dated to the beginning of the tenth century BC, glass vessels from Theban tomb 320 are characterized by low potassium and magnesium (< 1.2%), soda (18.2–23.4%), calcium (1.3–4.8%), and alumina (> 2.1%) and, most likely, were made from sand and mineral soda (Schlick-Nolte & Werthmann, 2003). Natron-based glass, usually containing low levels of magnesia and potash (< 1.5%) (LMLK glass) and moderate levels of Al2O3 (0.5 to 3%) (e.g., Panighello et al., 2012), became widespread in the Southern, Eastern, and Western Mediterranean (e.g., Shortland et al., 2006). Some samples of the OINE m-Na-Ca type have very low levels of Al2O3 (< 0.5%) and low levels of some trace elements (m-Na-Ca LT), suggesting the use of silica sources different from that of the m-Na-Ca glass produced between the Hellenistic and Islamic periods. In the sample discussed, this type of glass is found mainly in the first through sixth century-AD bead types. Hence, they are labeled Roman glass (m-Na-Ca R).
Seventy-two samples have low levels of magnesia (< 1.5%), potash (< 1%), and low to moderate levels of alumina (1–3.5%), indicating the use of mineral soda as flux and sand as silica. All beads made of m-Na-Ca glass come from Nobadian graves, although many were reused Meroitic/Early Roman bead types (e.g., OINE05, 16, 22, 32, 33, 34, 36, 55, 71, and 72). The southeastern part of the Mediterranean basin and the Levantine coast owe their sand deposits to the Nile drainage into the Mediterranean Sea. The sediments flow, primarily the wave-induced longshore currents that cause changes in the proportion of selected minerals, may help determine certain glass types’ provenance. For example, declining ratios of zircons (Barfod et al., 2020) may serve as a criterion to separate Egyptian and Levantine glasses. Since Egyptian sand would contain higher zirconium concentrations, Egyptian glass should have lower yttrium to zirconium (Y/Zr) and cerium to zirconium (Ce/Zr) ratios when compared to glass from the Levant, produced from sand with lower Zr concentrations (Van Strydonck et al., 2018). Calculating the yttrium to zirconium (Y/Zr) and cerium to zirconium (Ce/Zr) ratios for the low-alumina soda-lime glass from Nubia would be indicative of an Egyptian provenance for OINE06, 15R, 16, 28Y, 32Bl, 33, 34, 36, 37, 41, 44, 55, 56, 71Y, 72, 75, 77, 78, and 80. A number of samples are of Levantine provenance (OINE06, 15R, 16, 28Y, 32Bl, 33, 34, 36, 37, 41, 44, 55, 56, 71Y, 72, 75, 77, 78, and 80) (Fig. 5A). The Ti levels for the OINE samples usually score low in the group of Levantine glass (< 400 ppm), confirming their attribution based on the Y/Zr and Ce/Zr ratios. However, some exceptions exist (OINE80, Levantine and Ti > 500 ppm; OINE44, 55, Levantine glass and Ti > 470 ppm) but to a limited extent. The Levantine glass in the OINE assemblage was partly identified for the Meroitic/Early Roman bead types (OINE16, 32, 33, 34, 36, 71, 72). Nearly all Nobadian translucent and semi-translucent blue glass beads feature comparable compositions with CuO, 0.3–1.8%, and antimony hardly present (OINE06, 37, 44, 66B, 71B, 75, 78, 80). The diagnostic Nobadian bead types, especially the wound bodies of eye beads and teardrop pendants (see below), appear to be made mostly of Levantine glass (Fig. 5B). Other beads (OINE05, 22, 55B) have elevated levels of CuO (1.6–2.4%) and significant quantities of Sb2O5 (0.6–1.2%).
Fig. 5A Ratios of Y/Zr to Ce/Zr showing Egyptian and Levantine origins for the low-alumina soda-lime subtypes; B Ratios of Y/Zr to Ce/Zr showing Egyptian and Levantine origins for Co and Cu blue glasses; C A biplot of Co/Ni versus Zn (ppm) in OINE m-Na-Ca Roman glass
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An elevated cobalt (555–1629 ppm) content was the main colorant of the dark blue beads (OINE02BCo, 09, 13, 15BCo, 16BCo, 25, 30, 31BCo, 33BCo, 34BCo, 35, 41, 55BCo, 72, 74, 81) and workshop chunks (OINE76–77). The cobalt used for the natron-type beads is not unambiguously associated with any particular impurities, a trademark of Roman cobalt sources (Gratuze et al., 1992). According to Gratuze et al. (2018), natron glass colored with cobalt features a relatively constant pattern with a high CoO/NiO ratio (CoO/NiO > 24). Sometime between the late fourth and the beginning of the sixth century, the CoO/NiO ratios experience a drastic decrease (2.2 < CoO/NiO < 5.1) (Gratuze et al., 2018, p. 18). In the OINE assemblage, only a few dark blue glass beads have a high Co/Ni ratio (> 24 for OINE16, 33, 72), while the glass of these Nobadian-dated beads may have been produced earlier, in the Meroitic period. Only one bead in the studied assemblage has a low Co/Ni ratio of 5.9 (OINE32). In contrast, most samples have ratios below 24 but higher than 5 (OINE02, 09, 13, 15, 25, 30, 31, 34, 35, 41, 55, 74, 76, 77, 81), which may have resulted from recycling earlier glass mixed with the glass of a later date (Fig. 5C). Many of these samples were made of Egyptian glass (Fig. 5B). It seems probable that the period between the late fourth and the sixth century was the time when earlier, Early Roman cobalt glass of Co/Ni ratio above 24 (Gratuze et al., 2018) would have been mixed with new resources characterized by the Co/Ni ratio between 2.2 and 5.1 (Gratuze et al., 2018).
The m-Na-Ca beads were made with diverse techniques, well recognized in Roman and late antique northeast Africa (e.g., Then-Obłuska & Wagner, 2019b) and beyond. These are beads made of drawn and segmented glass and gold-in-glass as produced in Alexandria, Egypt (Kucharczyk, 2011; Rodziewicz, 1984). Other beads were made of the wound, folded, and rod-pierced glass, and many of them might have been manufactured locally.
Nine m-Na-Ca samples (OINE59, 60Bl-Y, 61, 64Bl-B-Gr-W-Y) are characterized by very low levels of MgO, K2O, Al2O3 (\(\le\) 0.5%), and Fe2O3 (average of 0.8%). They also have low levels of silica-related impurities and other earth trace elements (e.g., Ti, Sr, La, Rb, and Ba) compared with the m-Na-Ca Roman glass type. Although OINE58 and 63 feature MgO, K2O, or Al2O3 levels higher than other examples in the m-Na-Na LT glass group, their trace elements (Sr) still fit the “low trace” natron group. For this reason, they have been assigned to the m-Na-Ca LT glass group.
The OINE m-Na-Ca LT composition suggests a very clean silica source, i.e., a better quality of sand or even quartz pebbles, for glass production (Shortland & Eremin, 2006). Based on the Zr level, two types of “classic natron” glass were distinguished: low-Zr and high-Zr natron glass (Conte et al., 2019). Low levels of Zr (< 9 ppm) and the lowest possible levels of alumina, magnesia, potash, iron, and REEs in a glass sample indicate, according to the authors, the use of quartz pebbles (Conte et al., 2019, table 4). However, the Zr level (> 21 < 272 ppm) in the OINE m-Na-Ca LT glass would point to a high-Zr affiliation, and this, in turn, would exclude the use of quartz pebbles. High lime concentrations in the m-Na-Ca glass came with sand collected from a beach and thus contained seashell fragments. A relatively low Sr content linked to a rather high CaO/SrO ratio (362) is thought to result from the addition of diagenetically altered shells, partly recrystallized once their initial strontium contents had been lost (Conte et al., 2019; Wedepohl et al., 2011).
As for the m-Na-Ca R glass, the authors compared yttrium to zirconium (Y/Zr) and cerium to zirconium (Ce/Zr) ratios of the m-Na-Ca LT glass samples with the ratios for glass produced in the Levantine and Egyptian regions, respectively. As shown in Fig. 5A, the m-Na-Ca LT glass samples follow a trend observed for glass samples of Egyptian provenance. Low Al2O3 (< 0.5%) levels undermine any comparison of the m-Na-Ca LT glass with most of the low MgO and K2O (< 0.5%) natron glasses from the eighth through the fourth century BC Europe (e.g., Macedonia; Blomme, et al., 2017). Still, similar compositions have been reported from various French sites, dated to the beginning of the Iron Age, in the ninth through second centuries BC (Gratuze, 2009, Fig. 2). One of these groups features low potassium and low alumina, each at a level of about 0.5%. Some samples in this group come from the Champlay context dated to ca. 750–500 BC or 750–400 BC (Gratuze, 2009, Fig. 2). An antimony decolored glass sample from Sardis (Turkey), dated to ca. 700–500 BC (Ignatiadou, 2000), and a turquoise decoration of the Bologna eye bead from 500–300 BC-Etruscan context in northern Italy feature similar very low Al2O3 results (Arletti et al., 2010, IG45). Interestingly, an opaque red chunk with MgO, K2O, and Al2O3, < 0.5%, was found in Persepolis, dated to around the fifth century BC (Brill, 1999, IIH:198). Additionally, a glass of probable Egyptian provenance, featuring Mg, K, and Al, < 0.5%, low levels of some trace elements that resemble the m-Na-Ca LT glass, and a so-called “classic natron,” was identified in the Iron Age Italy, ca. 800–500 BC (Conte et al., 2019).
The study by Conte et al. (2019), using the measurements of selected elements’ levels, also presents ways to date the natron black glass more adequately. Some black samples with low lime, high iron, and high trace and REEs contents are dated to ca. 900–700 BC. Other samples (TG3bl, TG12bl, and TG13bl), characterized by lower alumina, titania, iron, and higher lime concentrations, are comparable with the OINE m-Na-Ca LT, and dated to ca. 700–500 BC.
An analysis of opacifiers in the m-Na-Ca LT group confirms its early date. Yellow glass in OINE60Y and 64Y features significant Sb2O5 (1.2%, 1.1%) and PbO (15%, 9.7%) levels and a complete lack of tin. Antimony-based opacifiers (i.e., lead antimonate yellow) were used, in the Near East and Egypt, from the onset of glass production, ca. 1500 BC, through the Roman period (Turner & Rooksby, 1959). Towards the end of the Roman period (especially fourth century AD onwards), the production of opaque yellow glass would fall back on the use of stannate instead of lead antimonate (Tite et al., 2008). It was not until the late fifteenth century AD that the latter was reintroduced into glass production (Molina et al., 2014). OINE58 is translucent blue with CuO (1.2%), MnO, and Fe2O3 (0.4%). Like the blue glass in v-Na Ca NK (OINE65A), it does not contain tin.
An m-Na-Ca LT type bead (OINE64), decorated with colorful spots, belongs to a group of so-called crumb beads reported from contexts dated between the Late Bronze and the Medieval times (Spaer, 2001, p. 127). It was found along with other m-Na-Ca LT glass beads in a 25th Dynasty grave. The same context also yielded a quadruple wedjat eye, typical of the Third Intermediate Period (Williams, 1990). Comparing OINE64 black glass compositions with Italian samples (see above) suggests ca. 700–500 BC as a probable date. PXRF analysis of red “natron sodium-lead-calcium-magnesium-silica” glass beads from the Nubian site of Gala Abu Ahmed in Wadi Howar, dated ca. 1100–400 BC, provided no trace elements feasibly comparable with OINE glass (Daszkiewicz & Lahitte, 2013). Some compositional similarities in OINE58 can be recognized in an orange bead of Egyptian glass, featuring low levels of MgO, K2O, and Al2O3 (< 0.5%) (Then-Obłuska & Wagner, 2019b, SNM07). Its elemental levels (e.g., Al2O3 0.25%, Sr 93 ppm, Zr 13.8 ppm, and Ti 319 ppm) resemble those in m-Na-Ca LT glass; however, the NaO (2.98%) and CaO (1.8%) levels are much lower. The bead was found in a Sedeinga grave, accompanied by several other beads of the same type and Napatan amulets (Then-Obłuska, 2015b). A Napatan date for this glass type can be supported by evidence from Nag Shayeg, where beads of this type have been found in a probable Napatan tomb, T131 (Then-Obłuska & Wagner, 2019b, Pl. 28.1–28.2).
Four glass samples (OINE03, 45, 46, 53) with low alumina levels, moderate K2O (< 1.5%) level, and elevated concentrations of MgO (> 1.5%) suggest the use of mineral-soda and plant ash or the specific soda plant ashes. The K2O or MgO > 1.5% values are commonly believed to indicate the use of organic material in the form of plant or wood ash in the glass batch. Glass with higher concentrations of MgO or/and K2O was identified and discussed for early Roman glasses in Egypt (Nenna & Gratuze, 2009; Then-Obłuska & Dussubieux, 2016), and the Egyptian m/v-Na-Ca glass was found mainly in the first through mid-fourth centuries AD Nubia (Then-Obłuska & Dussubieux, 2021; Then-Obłuska & Wagner, 2019a). The present study confirms their Egyptian provenance (Fig. 5A), and the OINE m/v-Na-Ca glass beads in this assemblage were most probably Meroitic items reused in Nobadian graves.
Sixteen samples have high alumina (> 7%) and low magnesia (< 2%) concentrations, indicating the use of mineral-soda flux (m-Na-Al). The mineral-soda high alumina glass beads, with relatively high (> 5%) concentrations of alumina and trace elements, are particularly common in India where, undoubtedly, they were manufactured (Brill, 2003; Dussubieux et al., 2010, 2021). Low magnesia (< 2%) concentrations indicate the use of mineral-soda flux. Based on different trace element levels, two sub-types have been identified within the OINE assemblage: 15 samples were made of m-Na-Al 1 and one sample of m-Na-Al 2 (Fig. 6).
Fig. 6Principal components 1 and 2 calculated using the concentrations of MgO, CaO, Sr, Zr, Cs, Ba, and U for samples belonging to glass groups m-Na-Al 1, 2, 3, 4, and 6 and for samples from Nubia. The m-Na-Al 1 glass samples are unpublished data from Sri Lanka and South India, the m-Na-Al 2 glass samples are beads from Chaul (Dussubieux et al., 2008), the m-Na-Al 3 glass samples are beads from Kopia (Dussubieux & Kanungo, 2013), the m-Na-Al 4 are glass vessel fragments from Sumatra (Dussubieux, 2009), and the m-Na-Al 6 glass are from the site of Juani Primary School (Dussubieux & Wood, 2021)
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Fourteen samples in the OINE collection have high Al2O3 contents ranging from 7.1 to 13.4% (OINE01, 04, 07, 08, 12, 14, 18, 20,23, 39, 49, 50, 52, 79). The MgO concentrations in this glass are usually low (< 1%), while other trace elements, such as uranium with 4–24 ppm, have the highest concentration in this study. Dussubieux and co-authors distinguished a few subtypes of high-alumina mineral soda glass (m-Na-Al 1–4 and 6) based on the contents of five elements: Sr, Zr, Ba, U, and Cs (Dussubieux et al., 2010, tab. 3; Dussubieux & Wood, 2021). Using principal component analysis (PCA) and glass constituents, MgO, CaO, Zr, Sr, Ba, Cs, and U, the m-Na-Al glass beads found in Nubia were compared with already defined m-Na-Al subtypes (m-Na-Al 1–4 and 6), and they showed similarities with the m-Na-Al 1 glass (Fig. 6). The compositions of the 14 high alumina samples of this m-Na-Al 1 glass group (formerly known as “low uranium-high barium glass,” Dussubieux et al., 2010) have average contents of Ba and U that match the m-Na-Al 1 type (Table 2).
Table 2 Average concentrations and standard deviations of important elements crucial for separating m-Na-Al subtypes (data from Dussubieux et al., 2010), followed by data for the high-alumina glasses (m-Na-Al 1, m-Na-Al 2) from the Lower Nubian OINE collectionFull size table
Additionally, one sample, a green drawn and rounded bead OINE11, has a high concentration of MgO (3.3%), K2O (2.2%), and Al2O3 (5.6%), and low CaO (3.1%). The trace element levels match the m-Na-Al 1 group (Table 2). Also, the PbO (4%), CuO (0.8%), and SnO2 (0.5%) levels fit within the range for the green glass in the m-Na-Al 1 group. OINE11 was found in a Nobadian grave together with glass beads made of m-Na-Al 1 glass, which would confirm its affiliation with high alumina glass of South Indian/Sri Lankan provenance. The presence of lead and tin in OINE14 (PbO = 4.6%; SnO2 = 0.54%) suggests the yellow bead was probably colored and opacified by lead stannate. Six semi-translucent pale green samples, OINE08, 18, 23, 39, 50, 79, contain significant quantities of CuO (0.3–0.8%), PbO (2–5%), and SnO2 (0.3–0.6%), suggesting lead stannate may have contributed to the opacification of the glass. Seven beads, OINE01, 04, 07, 12, 20, 49, 52, are orange and contain high concentrations of copper (CuO 7.2–9.2%), but also a higher concentration of iron (2.3–3.1%) when compared to the blue, red, and black m-Na-Al 1 glass from both South Asia (Lankton & Dussubieux, 2006, p. 129, Table 2) and Nubian sites (Then-Obłuska & Wagner, 2019b). The orange samples are also characterized by high levels of MgO, K2O, and P2O5. Phosphorus and lime-rich inclusions were found in an orange m-Na-Al 1 glass sampIe from South Asia. These suggest a possible addition of an apatite-rich ingredient for internal reduction to convert the Cu2+ into Cu2O (Dussubieux et al., 2010) that usually colors glass orange.
The m-Na-Al 1 glass was most probably manufactured in Sri Lanka or South India. Beads made of this glass are found in Sri Lanka and South India, between the second/first century BC and fifth century AD; and in Southeast Asia between the fifth century BC and tenth century AD (Carter, 2016; Dussubieux et al., 2010, tab. 4; Dussubieux & Gratuze, 2013). Aside from the Southeast Asian finds, the presence of South Indian/Sri Lankan glass beads has also been confirmed at the Early Roman Red Sea port of Quseir, Egypt (Then-Obłuska & Dussubieux, 2016), in Merovingian-period Europe (Pion & Gratuze, 2016; Poulain et al., 2013), and Zanzibar, AD 700-1100 (Sarathi et al., forthcoming; Wood et al., 2017).
The South Indian/Sri Lankan glass (m-Na-Al 1, — green, orange, black, yellow, and orange-on-red) has been found in the Nubian Nile Valley between the First Cataract and the confluence of the Niles (Then-Obłuska & Wagner, 2019a, b), including the mid-fourth century AD samples from the cemeteries of nomadic peoples (Blemmyes) around Kalabsha, representing the northernmost presence of these glass beads in the Nile valley (Then-Obłuska & Dussubieux, 2021). Beads made of m-Na-Al 1 glass were produced using a technique diagnostic of Indian origin—drawing a glass tube and heat-rounding its sections (Francis, 2002). South Indian or Sri Lankan glass beads have also been macroscopically identified at other sites associated with the Blemmyes: the Early and Late Roman Red Sea port sites of Berenike and Marsa Nakari (Francis, 2002, 2007; Then-Obłuska, 2016, 2017b, 2018a, 2019, 2021) and the Eastern Desert sites of Shenshef and Sikait (Then-Obłuska, 2017a, 2021), thus pointing to the east–west direction of South Asian bead distribution in northeast Africa.
One sample, OINE57, has low levels of MgO (1.1%) and K2O (1.8%) and a high level of Al2O3 (8.5%), pointing to its mineral soda high alumina affiliation. When compared with m-Na-Al 1 glass (Table 2, Fig. 6), it displays higher concentrations of U and Cs and lower concentrations of Ba, Sr, and Zr and fits the m-Na-Al 2 group as defined by Dussubieux et al. (2010). The CuO (0.7%), PbO (2.4%), and SnO2 (0.4%) levels in the green glass suggest the use of lead stannate. The m-Na-Al 2 glass was previously identified at sites dating from the ninth to the nineteenth century AD, located on the west coast of India and the east coast of Africa (Dussubieux et al., 2010). A recent analysis of more beads from the East African coast has helped revise the chronology for this glass and suggested its presence from around the fourteenth century AD onwards. The Indo-Pacific Khami beads from Southern Africa and m-Na-Al 2 beads on the East African coast have been identified as sharing the same composition. Therefore, both can be assigned to around the fourteenth century AD (Dussubieux & Wood, 2021). Although the m-Na-Al 2 glass beads might have been manufactured in Maharashtra, a recent study using Sr, Nd, and Pb isotope analysis suggests that the raw glass was likely procured from a different region, possibly western Uttar Pradesh (Dussubieux et al., 2021). The beads would have been traded across the Indian Ocean through Chaul, south of Mumbai (Wood, 2019). OINE57, found in grave VF68, originally was strung together with other drawn green and black beads and a Mediterranean Sea coral (Corallium rubrum sp.). Since the latest evidence for m-Na-Al 2 glass suggests a new fourteenth century AD dating for the Qustul VF68 grave, it appears fairly probable that the beads and grave may belong to the Islamic period in Lower Nubian history.
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