The glass-melting crucibles of Derrière Sairoche (1699–1714 AD, Ct. Bern, Switzerland): a petrological approach

Structural and vibrational characterization of medieval like glass samples

“…The melting temperature of PLS medieval glass was almost 1350°C [16] and would correspond to I p values higher than 4 [87]. The low I p values suggest that the annealing, usually performed in the temperature range between 650-700°C [16] is the thermal treatment responsible for the medieval glasses polymerization degree.…”

“…The most characteristic chemical features of glass used in the Middle Ages for the production of cathedral windows in Central Europe are low levels of SiO 2 (often lower than 60 wt.%), high levels of K 2 O (12-26 wt.%) and CaO (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27) wt.%), and the presence of P 2 O 5 (1-6 wt.%) and MgO (2-7 wt.%) resulting from the use of beech and fern ashes as fluxing agents after about 1000 AD [1][2][3][4][5][6][7][8][9]. This kind of glass, known as PLS (Potash-Lime-Silica glass), was produced by mixing one part washed sand, or ground quartz pebbles, and two parts beech wood ash, as testified by the Benedictine monk Teophilus in "De diversis artibus" [10,11].…”

“…Once ready, the melt was blown, worked into objects, and then placed into an annealing oven [10,11,14]. The development of crucibles with high thermal and mechanical resistance was also necessary [15][16][17], resulting in them being made in white (kaolinic) clay fired at temperatures above 1300°C [10]. In this way mullite was obtained, responsible of the thermal resistance of the so-called Hessian crucibles [18,19], the use of which is attested in Germany from the 12th century.…”

Pre-industrial glassmaking in the Swiss Jura: the refractory earth for the glassworks of Derrière Sairoche (ct. Bern, 1699–1714)

“…Several outcrops of pure quartz sand and refractory earth are historically known near Derrirre Sairoche (Schlaich 1934;Amweg 1941); however, to obtain a better understanding of the role of the raw materials and their influence on local glass technology, an archaeometric characterization appears necessary. In a recent paper Eramo (2005b) showed that the crucible samples of Derriere Sairoche were not tempered with recycled crucibles and refractory fragments ('grog') as suggested in old glassmaking treatises. Nevertheless, some processing of the raw materials cannot be excluded (e.g.…”

Roman double-layered crucibles from Autun/France: a petrological and geochemical approach

“…This range is generally higher than temperatures described for Roman metal-melting crucibles in literature (Freestone, 1989;Hein et al, 2007;Rehren, 2003;Tylecote, 1982). However, such high pre-firing temperatures are already reported from a 15th/16th century excavation in Hesse/Germany (Martinón-Torres et al, 2008) and from the 17th century glass-melting crucibles from Derrière Sairoche/Switzerland (Eramo, 2006).…”