Roman blue-green bottle glass: chemical–optical analysis and high temperature viscosity modelling

Abstract

Chemical analysis, optical absorption spectroscopy and mathematical modelling of high temperature viscosity have been carried out on five 1st–2nd century AD Roman blue-green bottle glass fragments from Coppergate, York. Modelled viscosities indicate remarkable consistency within the sample set studied and support the suggestion that temperatures of ∼1000–1150 °C were required to remelt these glasses and to provide suitable viscosities for forming articles. Iron redox ratios (Fe 2+/ΣFe), analysed SO 3 contents and the absence of characteristic Fe 3+–S 2− amber absorption bands suggest that melting conditions for all studied glasses were mildly, rather than strongly, reducing (estimated pO 2 ≈ 10 −1–10 −6 bar). These furnace conditions are consistent with the effects of combustion gases and carbonaceous matter contained in the raw materials.