Glass Provenance and Recycling as Evidence for Production Cycles, Self-Sustainability and Urban Networks

The 2012-2015 campaigns of the Danish-German Jerash Northwest Quarter Project in Jerash, Jordan, revealed numerous glass artefacts, raw glass and glass slag, testifying, on the one hand, to the use and consumption of glass and, on the other hand, intensive glass production in Jerash. The studies - archaeological, chemical and isotopic - of glass artefacts within the framework of UrbNet and the Danish-German Jerash Northwest Quarter Project show that the nature of these activities was a secondary glass working process, rather than a primary. Furthermore, they attest to Byzantine raw glass of the type Levantine I being imported from large-scale glass production centers on the Mediterranean coast. Here, on the Levantine coast with beach sand, glassmakers mixed shell-bearing sand with natron (soda) formed naturally on dry salt-lake beds, most likely from Wadi el-Natrun in Egypt.

Systematic elemental variations in glass from Jerash allow us to identify the range of minor minerals in the sands used for this glass production, providing new critical clues about the raw materials. While raw glass was not produced in Jerash, the trace elements reveal that recycling of the glasses occurred extensively and was well-organised. Glass was systematically collected and remelted, which is reflected in the well-correlated trace-element trends among the glasses.

The more the glasses were recycled (i.e. re-melted), the higher the incorporated amounts of contaminants from fuel ash and furnace walls became. The local nature of the recycling processes and the narrow range of the chemical composition of the imported glass afford an opportunity to study these competing processes in such detail that, for the first time, we can identify the behaviour of minor elements, such as e.g. vanadium, arsenic, zirconium, thorium and uranium during these processes.

The implications of these studies are promising. They indicate a relatively high self-sustainable nature of glass recycling in Jerash, which in turn allows for the detailed characterisations of the ancient recycling processes. The intention is to expand the glass studies further to include raw imported glass and glass slag, as well as a detailed trace-element study of sand from the Levantine coast, which has never been undertaken. Complimentary studies of other materials, such as iron, ceramics and semi-precious stone, will be carried out in parallel studies in order to allow for comparison of recycling scales with other material categories.

Investigators: Assistant professor Gry H. Barfod (Aarhus University), Professor Achim Lichtenberger (Ruhr-Universität Bochum) and Professor Rubina Raja (Aarhus University).