Scientific analysis of the glass and the glass-bearing artefacts: Technique, raw materials used and archaeological interpretation

The reasons for carrying out a scientific investigation of the glass from Wijnaldum are both technological and archaeological. The chemical compositions of ancient glasses can provide an indication of the kinds of primary raw materials used to make the glass, the impurities which were introduced with the raw materials and the means by which colours were achieved. In almost every case it is possible to use the chemical composition of the glass as a means of characterising the glass to the time of production and very occasionally to a specific region or workshop site in which it was made. As more Early Medieval glass from Europe is analysed, it has become apparent that there are clear technological traditions which can be distinguished from each other amongst the glass which are sometimes correlated to the context date of the glass and to the vessel forms 1 ; this suggests that different vessel types (and the glasses themselves) were made in a range of production centres. 2 This evidence also suggests strongly that glass recycling did not occur widely, or these fine compositional distinctions would be lost. Early medieval glass can also sometimes be distinguished compositionally from that made in the preceding ‘Roman’ technological tradition. Glass production sites are a rarity in Early Medieval Europe (even if the analytical data suggests otherwise); the evidence for the fusion of glass from its primary raw materials (fritting) is especially rare. There is some evidence for the manufacture of glass cables that were used for decorating beads and vessels, such as at Barking, Essex, England and at Ahus, Sweden and also for making glass beads themselves by working glass. A far more common situation, however, is that production zones inferred from distributions of early medieval glass vessels based on vessel forms or their colours can not be related to industrial evidence for their production. At least at Wijnaldum there is primary evidence for working opaque yellow glass: such glass has been found attached to a thick layer of baked ceramic material and was probably used for making simple wound glass beads. On the basis of this evidence we can not, however, suggest that glass vessels were manufactured from hot glass or that glass was fused from raw materials at Wijnaldum.