Chemical characterization of glass beads from the necropolis of Dren-Delyan (6^th–4^th century BC), Southwest Bulgaria

The glass beads from the Dren-Delyan necropolis are found in burial complexes dated as from the end of the 6^th century BC until the first half of the 4^th century BC. The purpose of this study is to obtain data on the chemical composition of the glass and the technology of its production. LA-ICP-MS and SEM-EDS analyses were conducted.
   The analysed glass beads are classified as a low-magnesium type (LMG), and only one of the samples is determined as high-magnesium glass (HMG). The yellow colour of the glass is due to crystals of lead antimonate incorporated into the glass matrix. The green colour of the beads is a result of interaction of added copper and lead in the glass mixture, in presence of iron and chromium. Dark blue samples are coloured by additives with cobalt, copper and lower iron content. Light blue colouration of opaque glass beads is due to high copper content, along with the presence of iron. The colouring agent of a transparent light blue bead is FeO in amount up to 0.25 wt%. The brown colour is associated with high iron content. Two different opacifiers were used for the production of opaque glass beads – antimony and tin, either individually or together. The decolourising agent is antimony without the involvement of manganese. Based on the results of the studied glass beads, we assume at least four types of raw material mixtures for their production. Comparison of the obtained results and published data about similar ancient glass findings was made.