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

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 (Fe2+/ΣFe), analysed SO3 contents and the absence of characteristic Fe3+–S2− amber absorption bands suggest that melting conditions for all studied glasses were mildly, rather than strongly, reducing (estimated pO2 ≈ 10−1–10−6 bar). These furnace conditions are consistent with the effects of combustion gases and carbonaceous matter contained in the raw materials.