On the making, mixing and trading of glass from the Roman military fort at Oudenburg (Belgium)

Abstract

This paper presents the analysis of decoloured and naturally coloured glass from well-dated contexts in the southwest corner of the Roman fort at Oudenburg (Belgium) ranging from the late second to the early fifth century AD. The aim is threefold. First, provide comparative material in the study of glass consumption from the northwestern provinces of the Roman Empire. Secondly, evaluate possible diachronic shifts in the applied decolourizing agent to produce colourless glass as to assess potential correlations between glass production recipes, provenance and chrono-typology. Finally, provide an added value to the research of glass recycling and mixing in the Roman imperial period. Nine subgroups are distinguished based on their chemical composition determined by LA-ICP-MS: Sb-only, two groups of Mn-only, four groups of mixed Mn-Sb, HIMT and one glass without any decolouring agent. The Sb-decoloured glass is used in the earliest phases and can be attributed to an Egyptian provenance. The two subgroups of Mn-glass likely come from different provenances: one from Egypt and the other later one from the Levant. Most of the glass shows high marks of mixing based on high trace elements concentrations and the simultaneous presence of antimony and manganese. Inhomogeneous mixing of manganese and antimony was also detected through μXRF. One Mn-Sb subgroup likely comes from mixing antimony glass with HIMT. The obtained results help better recognise the shifts in applied glass recipes throughout the Roman imperial period and improve our understanding about the mixing and recycling of glass to supply a Roman military camp.

50 shades of colour: how thickness, iron redox and manganese/antimony contents influence perceived and intrinsic colour in Roman glass

“…Although the glass samples from Padova and San Genesio are dated beyond the main chronological range considered here, their chemical compositions (Silvestri et al 2014;Mendera et al 2017 The averages and standard deviations of main elements of the present dataset are given in Table 1. It should be stressed that, although chemical data of the glass considered here, except for reference glass, were determined in previous studies by means of different analytical methods and instruments during a span of about 10 years (Silvestri et al 2008(Silvestri et al , 2014Silvestri 2008;Ganio et al 2012;Gallo et al 2013;Mendera et al 2017;Bidegaray et al 2019), the results are perfectly comparable on the basis of the good precision and accuracy of the different techniques for major and minor elemental analysis.…”

“…These supplementary data were made identifiable by adding a letter (b or c) to the end of sample label (Appendix). The present dataset was previously characterised by the chemical point of view and results are detailed elsewhere (Silvestri et al 2008(Silvestri et al , 2014Silvestri 2008;Ganio et al 2012;Gallo et al 2013;Mendera et al 2017;Bidegaray et al 2019); here it is analysed using optical absorption spectroscopy.…”

“…Error on the total concentration of iron was also taken into account as reported in the literature (Silvestri et al 2008(Silvestri et al , 2014Silvestri 2008;Ganio et al 2012;Gallo et al 2013;Mendera et al 2017;Bidegaray et al 2019).…”

“…It nevertheless represents a relatively long-lived site in the northwestern provinces along important cross-channel trade routes between the Rhine region and Britain. An earlier chemical study on a selection of 90 colourless and naturally coloured glasses, covering the different archaeological sequences, identified various compositional groups: antimony-only, manganese-only, mixed antimony-manganese, HIMT, and one glass without any decolouring agent (Bidegaray et al 2019). Included in the present study were seven antimony samples, five manganese samples, 36 mixed manganese-antimony samples, 11 HIMT samples, and one "Fe alone" sample (i.e., glass with iron as the only colouring element and no decolouring agents).…”

“…Therefore, for all elements discussed here (i.e., iron, manganese and antimony), the between-group variation, meaning the difference between group averages, was higher than the analytical variability, as also demonstrated by relative standard variations of iron, manganese and antimony calculated among the considered groups, which are higher than 10%. (Silvestri et al 2008;Silvestri 2008); of Embiez from (Ganio et al 2012); of Adria and purple glass from (Gallo et al 2013;Silvestri et al 2014;Mendera et al 2017), of Oudenburg from (Bidegaray et al 2019…”