Fig. 5

Case Study II. Serravalle Castle, CH-Ticino and Venice Lagoon, Italy. Left column Serravalle, excavations by W. Meyer and S. Bezzola, mainly 14th century N = 95. Analyses by A. Burckhardt, ED-XFA Geochem. Lab. Univ. Basel, unpublished. a The large group represents 83% of the total consisting of elevated phosphate/sodium glass (right), and a small group (17%) consisting of high phosphate/low sodium (left). High sodium glass (index >0.95) as is typical for glass produced from geogenic soda is not present. c The large group represents probably glass made from native halophyte ash, P₂O₅ >0.20 wt%. Right column Venice Lagoon, 13th/16th century (Brill 1999; Verità 1985; N = 80). b Glass from Venice Lagoon consists of at least three compositional groups. One (small blue circles) represents according to a tentative interpretation Na–Ca glass made from native ash of halophile plants, one (large blue circles) consists of Na–Ca glass made from soda extract, one small group (blue crosses) might represent soda glass produced with geogenic soda, type “Wadi Natrun”. d displays glass containing >0.20 wt% P₂O₅, where highly soluble oxides like Na₂O are enriched, whilst less soluble ones are depleted as represent by arrows. This preliminary interpretation needs verification by experimental research