Pre-industrial glassmaking in the Swiss Jura: the refractory earth for the glassworks of Derrie`re Sairoche (ct. Bern, 1699–1714) G. ERAMO Department of Geosciences, Mineralogy and Petrography, University of Fribourg, Chemin du Muse´e, 6, CH-1700, Fribourg, Switzerland (e-mail:
[email protected]) Abstract: Fragments of the melting furnace and several crucibles of the glassworks of Derrie`re Sairoche are compared with local raw materials. Principal component analysis (PCA) based on the chemical composition and on the grain-size distribution of the archaeological and natural materials demonstrates that the analysed samples were made from the same raw material and that local clayey sands (Hupper, Side´rolithique) were exploited. Availability in situ of good raw materials made tempering unnecessary. Their high melting point (c. 1600 8C) allowed good performance in service conditions at tempera- tures up to 1500 8C. Moreover, because of low Fe2O3tot concentrations, batch-glass contamination was avoided. In the Middle Ages the spread of wood-ash glass materials and their influence on local glass production (‘Waldglas’) in northern Europe technology, an archaeometric characterization implied substantial changes from the natron appears necessary. In a recent paper Eramo glass produced in antiquity. The high CaO (2005b) showed that the crucible samples of (10–20 wt%) content of the former required Derrie`re Sairoche were not tempered with higher melting temperatures (up to 1400 8C) recycled crucibles and refractory fragments than the 1000–1100 8C range sufficient for the (‘grog’) as suggested in old glassmaking trea- ancient Na–Ca glasses (Turner 1956; Cable & tises. Nevertheless, some processing of the raw Smedley 1987; Cable 1998; Brill 1999; materials cannot be excluded (e.g.