Rare Alkali Elements as Markers of Local Glass Working in Medieval Tolmo de Minateda (Spain)

Abstract

Analytical data of Roman and early Islamic glass established several primary glass production groups linked to glassmaking centres in the Levant and in Egypt. In contrast, the activities of secondary glass workshops are largely invisible in the compositional fingerprint of first millennium glass. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of 261 glass finds from the Visigothic settlement of Tolmo de Minateda (Spain) revealed a site-specific contamination pattern due to secondary glass processing and recycling, namely the enrichment of the glass batch by a unique combination of rare alkali elements (Li, K, Rb, Cs). With a median of 21 ppm, Li is particularly distinctive. Elevated lithium contents (Li > 30 ppm) are also one of the characteristic features of Iberian plant ash glass from the Islamic period. The earliest known examples of this type of glass were found among the ninth-century remains from Tolmo.

Early Islamic glass (7th– 10th centuries AD) in Unguja Ukuu, Zanzibar: A microcosm of a globalised industry in the early ‘Abbasid period

“…It is possible to separate plant ash glass into broad compositional groups but using major and minor elements it can be difficult to define with confidence compositional subgroups which could reflect sub-regional production zones. For instance, although it is possible observe trends in the data which coincide with regions, it is nearly impossible to separate Levantine and Syrian glass with major and minor elements such as Al 2 O 3 , MgO, CaO, Na 2 O and K 2 O [ 7 , 28 ].…”