Materials characterization of 5th-6th century early Byzantine glass tesserae from Sinop Balatlar Church (Black Sea region, Türkiye)

Abstract

This study presents the first comprehensive archaeometric investigation of Early Byzantine glass tesserae from the Sinop Balatlar Church excavation and represents the first detailed analysis of glass artifacts from Türkiye’s Black Sea region. The majority of the studied tesserae are dated to the 5th -6th centuries CE, providing insights into the composition, production technologies, and raw material sources of these tesserae. A combination of analytical techniques, including laser ablation - inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscope-energy dispersive x-ray spectroscopy (SEM-EDS), was employed to determine major, trace, and rare earth element compositions, as well as crystalline phases, textural and microstructural features. The results indicate that the samples are soda-lime-silica glasses, with SiO2 contents ranging between 51 wt% and 75 wt%. Most samples exhibit low levels of MgO and K2O (< 1.5 wt%), suggesting the use of natron as a flux, while two samples display higher concentrations of MgO and K2O, indicating the possible use of plant ash. The study also identifies various coloring, decoloring, and opacifying agents, including Cu, Fe, Mn, Sb, and Pb, which were used to achieve different hues and opacity levels. XRD and SEM-EDS analyses confirm the presence of crystalline phases such as metallic native copper, lead stannate, bindheimite, and hexagonal calcium antimonate, contributing to the coloration and opacity of certain tesserae. Additionally, Late Roman metal-leaf-covered tesserae- dated to the 4th century CE- were analyzed, revealing a relatively pure gold coating. Elevated Mn and Sb concentrations in several samples suggest that glass recycling was practiced during this period. Various forms of degradation were also observed. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.