CHARACTERIZATION OF THE CHEMICAL COMPOSITION OF MEDIEVAL GLASS FINDS FROM SOUTH BULGARIA

Abstract

PIXE and PIGE were used for determination of 23 elements in 50 glass samples excavated in Zlatna Livada – South Bulgaria (dated 11 th -12 th century AD). Elemental concentrations show that the analyzed fragments belong to soda-lime-silica glasses. Cluster analysis and bivariate plots in- dicate the use of natron, plant ash and mixed alkalis as well as production according Near East and Roman-province recipes. The metal oxides responsible for coloration were also investigated. The blue and blue-green colors are due either to CoO or to high concentration of FeO (blue: 3.3-6.3%, blue-green: 1.23-2.83%), melted in reducing atmosphere. The melting under oxidizing environment determined the higher oxidation state of iron oxide and the green color of some of the glasses (0.7- 3.4% Fe 2 O 3 ). Different shades of brown color are due to the high concentration of Fe 2 O 3 (2.4-4.9%) and Mn 2 O 3 (0.3-0.7%) melted in oxidizing atmosphere. Discoloration of the glasses is achieved by the presence of high amount of MnO (0.6-2%). A comparison to other medieval Bulgarian glasses was performed.