Analytical and technological examination of glass tesserae from Hagia Sophia

A collection of nine coloured glass tesserae from Hagia Sophia, Constantinopolis is analytically studied aiming at the characterisation of the base glass used and its technology production, as well as at the diagnosis of its preservation state. A variety of non-invasive techniques like Fibre Optics Microscopy (FOM), Scanning Electron Microscopy with Energy Dispersion X-ray Analysis (SEM-EDS), X-ray Fluorescence (XRF), and Prompt-Gamma Activation Analysis (PGAA) are used for the analytical examination of the glass tesserae of different colourings. Additionally, and of great importance, is an attempt to estimate its chronological framework and, further, to produce provenance assignments, based on the statistical evaluation with parallels from published studies of other Byzantine monuments of Early and Late Byzantine Era. It is concluded that all the examined tesserae which were found severely deteriorated, are Early Byzantine natron glasses produced in the Levant, with the exception of a dark blue individual tessera having a Byzantine-Syrian origin of a latter period (Middle Byzantine). Furthermore, based on compositional similarities, use of tesserae transported by the Constantinopolis artisans for the decoration of parts of the mosaics at the palaeo-christian monuments of Ravenna and Padova in Italy, holds a great probability. Finally, well known Early Byzantine church monuments from Thessaloniki, Greece, followed statistical evaluation, found as to have used tesserae of the type likewise Hagia Sophia, but also plant-ash tesserae of an Eastern Byzantine origin; the latter indicating posterior construction or modification phases of the monuments' mosaics.