A non-destructive approach for the characterization of glass artifacts: The case of glass beads from the Iron Age Picene necropolises of Novilara and Crocefisso-Matelica (Italy)

Abstract

A totally non-destructive approach was employed to characterize beads from two Picene necropolises (Novilara-PU and Crocefisso-Matelica-MC) dating back to between 9th and 6th centuries B.C. Investigations were carried out principally by means of Reflectance Spectroscopy determining Co2+, Cu2+ and Fe3+ as the main chromophores, and by Raman Spectroscopy to distinguish samples realized with other materials, in particular bones and shells were recognized. Furthermore, Raman spectroscopy identified hematite as a coloring phase in the unique red bead discovered as unmelt crystals in blue and yellow beads. Additionally, X-Ray Diffractometry investigations indicated Ca-phosphates, bindhemite and the less common brizzite, as opacifiers in white and yellow beads, while chemical data collected through X-Ray Fluorescence evidenced differences between findings from the two localities and/or within the same site. Beads were found to belong to the Low Magnesium Glass (LMG) and High Magnesium Low Potassium (HMLK) classes with most blue beads being comprised of cobaltiferous alum salts and a relatively impure sand, and a calcareous sand having been used for all other analyzed beads. Finally, differentiations performed on the basis of MgO amounts tended to indicate the samples from Crocefisso as being more similar to Bronze Age compositions than the Novilara ones which are closer to typical Iron Age proportions. In addition, high amounts of lead have been detected in all the yellow beads, but they could be positively correlated to Sb2O3 only for samples recovered in the Novilara necropolis, thus indicating the use of lead antimonates as coloring agents.