Fig. 4
From: Phosphate: a neglected argument in studies of ancient glass technology
Case Study I. Pre-industrial K–Ca glass from Swiss Jura and German Black Forest. Left column glass hut Court Chaluet, operational 1699–1714 (Gerber and Stern 2012, N = 220) a Phosphate vs Alkali-index. c Phosphate vs main components indicating the effect of ash-processing (arrows different slope of soluble K2O and less soluble oxides of Mg, Al, Ca, Fe). e Ternary diagram with chemical main components SiO2, K2O, CaO and melting diagram after Morey et al. (1930) displaying naturally coloured wood-ash glass made from native wood-ash (red crosses) and colourless potash extract glass (red circles). g Same diagram with average glass compositions from glass-hut Court Chaluet (c) and Black Forest (b), wood-ash glass vs potash extract glass. Right column Black Forest, selected glass fragments from 37 glass huts of the 12th to 18th century. Data from Maus and Jenisch (1999), N = 102. b Phosphate vs Alkali-index. d Phosphate vs main components, caption same as from c. f Ternary diagram, captions same as from e. h Phosphate vs estimated year of production (naturally coloured forest glass and colourless potash extract glass). Potash extract glass is present since earliest documented huts and is present also as coloured window glass (ca. 1300 AD) in Freiburg i.B. cathedral (Brill 1999, large red circles)