Achaeometrical Research in Hungary II., 1988
ANALYSES - GLASS - Edit MESTER - István SZABÓ: Research of medieval glass vessels and glasshauses in Visegrád and Diósjenő
Fig. 5: SEM micrograps of the cross section of the weathered medieval glasses from the royal residence in Visegrád. Fissures and cracks penetrate the surface zone of samples and advanced into the bulk of the palish green (No. 1 and No. 2) and brown (No. 3) glass samples. (E. MESTER, I. SZABÓ, 1997.) Venetian glasses Ancient Romain glasses Venetian type glass vessels from Visegrád Venetian type glass from France Si0 2 69.51 68.56 67.98 65.4 Na 2 0 19.39 17.97 12.15 15.4 к 2 : 2.96 1.21 3.39 3.5 CaO 5.75 6.76 13.22 10.2 other oxides 3.51 6.5 4.36 6.5 Fig. 4: Average compositions of Venetian type glasses (weight-percent) (E. MESTER, I. SZABÓ, 1997., D. FOY, 1985., K. HETTES, 1963.) From the results of the ICP-OES examinations, given in mg/kg, we concluded, that the dark brown glass sherds have the highest content of Mg, Fe and Ni, 8517.70, 6271.39 and 143.82, respectively. The concentrations of Zn (136.71) and Cu (101.62) are not particularly high, but still significant. These latter data are responsible not only for the dark brown colour, but for poor chemical durability as well. In order to study the durability of glass, Newton introduced (and later Gillies and Cox applied) a method of representing its chemical composition expressed as the molar percentages of three reduced variables (NEWTON, 1975: 161-168; COX, 1979: 54-75; BARRERA, 1989: 48-54). These values H Si0 2 ", '*R 2 0" and "RO" group together as the network formers, and the monovalent and divalent network modifies, respectively. In this paper "Si0 2 " includes Si0 2 , P 2 0 5 and PbO and also twice the amount of trivalent oxides A1 2 0 3 , Fe 2 0 3 and Cr 2 0 3 . The term "R 2 0" is the sum of the concentration of Na 2 0 and 101
