High‐boron and High‐alumina Middle Byzantine (10th–12th Century ce) Glass Bracelets: A Western Anatolian Glass Industry

Abstract

The trace element boron is present in most ancient glasses as an impurity, and high boron (≥ 300 ppm) marks raw material sources that are geologically specific and relatively uncommon. Recent analyses of Byzantine glass with high boron contents suggest that glass‐making was not limited to the traditional regions of the Levant and Egypt, and a production origin in or near western Anatolia is proposed. Glass bracelets from Ḥiṣn al‐Tīnāt in southern Turkey give fresh evidence for the production and circulation of high‐boron glasses that closely correlates with object typology. The patterning of findspots suggests that high‐boron glass was closely connected to the Byzantine world.

A unique recipe for glass beads at Iron Age Sardis

“…Two main groups were described in the glass of Pergamon: the first is dark blue HBAl glass (characterized by B around 1000ppm, Al2O3 around 9wt%, CaO around 5wt% and Sr around 300ppm), while the second is transparent HLiBAl glass (characterized by B around 1500ppm, Li around 300ppm, Al2O3 around 4-7 wt%, CaO around 8-11wt%) . Swan et al (2018) reports compositional groups which are similar but distinct. Of interest for our work is the dark blue glass of group 2 (characterised by B between 1000-2000ppm, Al2O3 between 9.5-11 wt% and Co between 100-500ppm).…”

“…It seems this glass tradition with elevated B, Al and/or Li, of which the glass from Sardis is an early example, continues or is reused, from the first century CE onwards in Pergamon and more generally in Western Anatolia during the Byzantine period , Swan et al 2018. These later glasses are often dark blue but coloured with cobalt, whereas the black glass from Sardis is coloured by iron (similar to the Romanian glass) (Bugoi et al 2016).…”

“…In recent years high alumina glasses have been identified in Western Anatolia (Dussubieux et al 2010, Schibille, 2010and Swan et al 2018, Bulgaria (Bugoi et al 2016) and Italy (Neri et al 2019). Most of these occurrences are connected to the Byzantine period, although in Pergamon high alumina glasses are found as early as the first century CE.…”

“…This second option thus not only complies more satisfactorily with the boron isotopic signature of the samples considered here, but would also explain the potash concentration and the potash to magnesia ratio found in the glasses. The Na-HCO3 springs have also been suggested as the source of flux for medieval high Al-B glasses (up to 3000 ppm B) from Ḥiṣn al-Tīnāt (Swan et al 2018). A clear direct link cannot be made for materials that are nearly two millennia apart, but the possibility of a continued production of this glass type in the region over a prolonged period is an intriguing one which warrants further study of glass assemblages in that region.…”

Evidencing Human Occupation of a Small Island Through Ancient Glass: The Case of Ustica (Palermo, Italy)

“…High alumina soda glasses are generally not found frequently, but they are recognized in assemblages such as 2 nd /1 st century BC-5 th century AD glass beads from Sri Lanka and South India (Dussubieux, Gratuze, & Blet-Lemarquand, 2010, tab. 4;Dussubieux & Gratuze, 2013;Carter, 2016) which were present in Early Roman Quseir, Egypt (Then-Obłuska & Dussubieux, 2016) and during Early Byzantine period in Europe (Poulain, Scuiller, & Gratuze, 2013;Pion & Gratuze 2016); 4 th -6 th century AD glass beads from upper Nubia in Africa (Then-Obłuska, Wagner, & Kepa-Linowska, 2019); 7 th -8 th century AD Asian glass beads imported to Scandinavia and north Germany (Sode, Gratuze, & Lankton, 2017); 7 th -10 th century AD in Zanzibar (Wood, Panighello, Orsega, Robertshaw, van Elteren Crowther, Horton, & Boivin, 2017); 8 th -12 th century AD glass bracelets from Ḥiṣn al-Tīnātand in Turkey (Swan, Rehren, Dussubieux, & Eger, 2018). Few red opaque glass beads of Asian production found in Scandinavia and northern Germany (defined as group 4) show the most similarity with USTRA-01 as both calcium and aluminum values are around 10 wt% (Sode et al, 2017, Figure 5).…”