Fig 1.
Spatial distribution of chemical glass groups in Ciudad de Vascos.
Fig 2.
Soda concentrations versus the sum of potash and magnesia of all glasses from Ciudad de Vascos.
The three main glass types are easily distinguished based on the sum of the alkali and alkaline earth components MgO and K2O.
Fig 3.
Compositional differences related to the silica sources of the natron glasses from Vascos.
(a) Titanium versus aluminium contents highlight differences in heavy element contents of the different glass groups; (b) different strontium to lime ratios imply different sources of calcium for Levantine I, HIMT and Egypt II; (c) means of selected trace element and REE data of the different natron groups normalised to the continental crust (MUQ [30]).
Fig 4.
Elements associated predominantly with the silica source of the plant ash glasses from Vascos.
(a) Titanium and aluminium concentrations identify different silica sources; (b) different correlations of zirconium and thorium separate groups 1, 2 and 3 more clearly; (c) means of trace and REE data of the five different plant ash silica groups normalised to the continental crust (MUQ [30]) confirm variations in the silica source.
Fig 5.
Computation of a mixed glass composition corresponding to group 5.
Averages of the group 3 (n = 12) and 4 (n = 31) compositions were normalised to the mean of group 5 (n = 28). A theoretical composition (groups 3 and 4 at a mixing ratio of 2:1) was calculated and normalised to group 5. Grey areas represent the standard deviation of the group 5 composition.
Fig 6.
Elements related to the plant ash component in the five different plant ash silica groups.
(a) Bivariate plot of CaO against the sum of Na2O, MgO and K2O; (b) B versus Na2O differentiates between types of plant ashes.
Fig 7.
Possible affiliations and provenance of the Vascos plant-ash glass.
(a) Aluminium and titanium concentrations in comparison with comparative material from the eastern Mediterranean in light grey from Tyre, Caesarea, and the Serçe Limani shipwreck [23, 76]; (b) distinction of the plant ash groups as a function of yttrium to zirconium and cerium to zirconium ratios.
Fig 8.
Possible affiliations and provenance of group 4 from Vascos.
(a) Aluminium and titanium concentrations in comparison with comparative assemblages from Qasar es-Seghir [23], al-Basra [71], Murcia [59] and Beja [60] in light grey as well as samples from Tuscany [64] and Silves (in preparation); (b) zirconium versus titanium contents highlight differences between Iberian glasses from Vascos and Silves (Portugal) and glasses from various Tuscan sites [64].