Fig. 7

Case Study IV, La Tène alkali-Ca glass. Tarodurum/D-Zarten and antiquity. Left column celtic Tarodunum/D-Zarten. Analyses by A. Burckhardt, ED-XFA Geochem. Lab. Univ. Basel (Wagner 2006; Burkhardt and Steuer 2006). a Phosphate vs alkali-index of 395 glass fragments. Roughly 5% consist of high phosphate high K₂O-glass (K, left circle), 10% represent low phosphate low K₂O specimens. c. Main oxides vs phosphate. e. Phosphate vs alkali-index of 47 high sodium glasses (index >0.95). g Ternary chemical diagram with inserted physical/melting data. Part displays a melting temperature probably over 1000 °C. Right column Egypt, Mesopotamia. Analyses from Brill (1999) and Shortland and Tite (2000), N = 50. b. Phosphate vs alkali-index. Most glasses from Egypt and Mesopotamia were probably made with native ash (P₂O₅ >0.20) and ash extract (P₂O5 <0.20), and roughly 10%, mostly Mesopotamian specimens represent probably geogenic soda glass. d Phosphate vs main oxides. f Late Roman vessel glass. Analyses: Ref. Foster and Jackson (2009, 2010), N = 220. Most blue flat glasses contain between 0.09 and 0.20 wt% P₂O₅; all colourless contain less than 0.08 wt% phosphate and over 0.95 Na₂O)/(Na₂O + K₂O) and may represent hence geogenic soda glass, type Wadi Natrun. These tentative attributions need experimental verification. h Ternary chemical diagram with inserted physical/melting data. Probable melting temperature between ≈850 and ≈950 °C