Production and provenance of architectural glass from the Umayyad period

Abstract

A large assemblage (n = 307) of architectural glasses (tesserae and windows) from the early 8th-century Umayyad residential site at Khirbat al-Minya was analysed by laser ablation inductively coupled plasma mass spectrometry. Trace element patterns are essential to establish the provenance of the base glass, while the comparative evaluation of the colouring and opacifying additives allow us to advance a production model for the manufacture of glass mosaic tesserae during the early Islamic period. The primary glass types are Levantine I and Egypt 1a, as well as a few older, reused tesserae, and Mesopotamian plant ash glass used for amber-coloured window fragments. Chemical data revealed fundamental differences in the colouring and opacification technologies between the Egyptian and Levantine tesserae. Co-variations of lead and bismuth, and copper, tin and zinc in the Egypt 1a tesserae provide first evidence for the production of different mosaic colours in a single workshop, specialising in the manufacture of tesserae of different colours. No such trend is apparent in the Levantine samples. Red, cobalt blue and gold leaf tesserae were found to be exclusively made from a Levantine base glass, indicating that the generation of some colours may have been a specialised process. The same may apply to the amber-coloured window glass fragments of Mesopotamian origin that exhibit very unusual characteristics, combining elevated copper (2% CuO) with an excess in iron oxide (5% Fe 2 O 3). These findings have significant implications for the production model of strongly coloured glass and the exploitation of resources during the early Islamic period.

Loose glass tesserae and lost decorations: chronology and production of mosaics from Gerasa's Northwest Quarter*

“…With the exception of the HIMT gilded tessera, which dates to the fourth or fifth century, the gold tesserae are roughly contemporary with the Levantine group, and can thus be also associated with the decoration of churches. Gold tesserae with a Levantine base glass composition were realtively common in Byzantine and early Umayyad Palestine, where they might have been manufactured (Gorin-Rosen 2015, Adlington et al 2020. This makes the exclusive import of Egyptian gold-leaf tesserae to Gerasa particularly intriguing, especially in view of the general lack of Egyptian primary compositional groups in Jordan at this time (Figure 6).…”

“…Gold tesserae with a Levantine base glass composition were realtively common in Byzantine and early Umayyad Palestine, where they might have been manufactured (Gorin‐Rosen 2015 , Adlington et al . 2020 ). This makes the exclusive import of Egyptian gold‐leaf tesserae to Gerasa particularly intriguing, especially in view of the general lack of Egyptian primary compositional groups in Jordan at this time (Figure 6 ).…”

A Tale of Two Legacies: Byzantine and Egyptian Influences in the Manufacture and Supply of Glass Tesserae under the Umayyad Caliphate (661–750 AD)

“…Data demonstrated that T1 tesserae have been made by using sands richer in the heavy accessory minerals and lower in the strontium contents; with low CaO (between 2.69 and 4.34 wt%) and high Na 2 O (16.87 and 19.38 wt%), these features are consistent with Egypt I compositional category. Green area: Apollonia-type glass [32][33][34], orange area: Jalame-type glass [35], red area-full line: Egypt I late antique/early Islamic glass [34,[36][37][38][39], red area-dotted line: Egypt I Wadi Natrun glass [40], purple area: Foy-2 glass [38,[41][42][43][44], Qusayr' Amra [45], Khirbat al-Minya [46].…”

“…Regarding the manufacture of mosaic tesserae, the use of Egypt I glass is a distinguishing feature of the Umayyad age. Apart from the quasr of Khirbat al-Mafjar, the Great Mosque of Damascus, and the Dome of the Rock, it has recently been found among assemblages of tesserae from the baths of Qusayr 'Amra [45] and Khirbat al-Minya [39,46].…”

“…The maps provided in Figure 6 show that glass tesserae matching Apollonia-type and Foy-2 compositional categories have mainly been recovered from sites located in the territories under the domain of Byzantium, datable back between the 5th and the 10th century, with a major amount from the 6th century. [39,41,44,46].…”