Figure 3: Na2O versus SiO2 (a), MgO versus K2O (b), Al2O3 versus CaO (c), and MnO versus FeO (d) contents of Greek glass samples, subdivided by provenance: Thessaloniki Agora (⋄), Maroneia (○), Thessaloniki, various sites (∆: natron glass; ▲: soda ash glass). Mean chemical compositions and standard deviations of main compositional natron groups, identified in literature and comparable with Greek samples, are also shown: “Roman” glass (bold plus sign), Group 2 (bold multiplication sign) [22, 35].