Chemical characterization of glass beads from the necropolis of DrenDelyan (6th–4th century BC), Southwest Bulgaria

Abstract

The glass beads from the Dren-Delyan necropolis are found in burial complexes dated as from the end of the 6th century BC until the first half of the 4th 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.

Known Glass Compositions in Iron Age Europe—Current Synthesis and Emerging Questions

“…The transition from the Bronze Age plant ash-based glassmaking tradition to natronfluxed glass is by no means clear-cut, as evidenced by the centuries-long parallel production and circulation of glass fluxed with natron and plant ashes throughout Europe during the early first millennium BCE, most notably in France and Italy [20,35,37,38,75,78,79,83]. In fact, studies of European glass beads and other artefacts in the last decade alone have shown that several different types of glass were in use throughout Europe during the 1st millennium BCE [33,[37][38][39]84]. The subdivision of glass types is based primarily on their MgO and K 2 O contents, but other elements, most notably Al and Fe, can be used to define further sub-types.…”

“…The few exceptions that exhibit MgO and K2O values similar to those of previously described glass types are some 6th-5th century BCE samples from Stična (Slovenia) which show MgO and K2O values compatible with the LMMK group ( Stična 42,44,45,51,51) [31], a mixed alkali (LMHK) sample from Slovenia (Stična 41) [31], and two coeval HMG (Wicina 68d) and HMLK (Mechlin 41) samples from Poland [39]. Slightly younger examples, dating from the 6th-4th centuries BCE, are even scarcer: a HMG sample (Bg) from Bulgaria [84]; two samples from Italy (IG 11b, IG 44b) [93] corresponding to LMHK and HMLK glass, respectively; and another HMLK sample (Stična 29) from Slovenia [31]. Of the mentioned samples, only the HMG glass plots falls into the plant ash soda-lime [31,33,[37][38][39][40]42,84,86,90,92,93].…”

“…Slightly younger examples, dating from the 6th-4th centuries BCE, are even scarcer: a HMG sample (Bg) from Bulgaria [84]; two samples from Italy (IG 11b, IG 44b) [93] corresponding to LMHK and HMLK glass, respectively; and another HMLK sample (Stična 29) from Slovenia [31]. Of the mentioned samples, only the HMG glass plots falls into the plant ash soda-lime [31,33,[37][38][39][40]42,84,86,90,92,93]. Glass family ranges were obtained from [10].…”

“…(b) Al 2 O 3 -CaO-FeO ternary diagram of glass from Europe roughly dated to the 6th century BCE. Data were taken from various publications [31,33,[37][38][39][40]42,84,86,90,92,93].…”

Archaeometric Analysis of the Objects from the Scala Santa (Holy Stairs) in the Crypt under the Piarist Church in Cracow (Poland)

“…Admixtures of Mg, Al and Zn are also characteristic of jacobsite [49]. It is possible that the higher Mg content (mean MgO 2.75 wt%) is the result of using jacobsite as a pigment (magnesium is a common admixture in Mn and Fe compounds [51]). However, magnesium may also come from the ash used as the flux.…”