Obsidian and Obsidian-like Glass Tesserae: A Multidisciplinary Approach to Study the Dedication Wall Mosaic in the Church of St. Mary of the Admiral in Palermo (12th Century)

Valentina Cantone,Ivana Angelini,Rita Deiana,Alberta Silvestri

doi:10.1515/opar-2020-0116

Abstract

AbstractPliny the Elder testifies that roman workshops used volcanic glass (obsidian), but also produced and used a dark glass (obsidian-like glass) quite similar to the natural one. In the context of the study on medieval mosaics, the use of the obsidian and obsidian-like tesserae is a challenging research topic. In this paper, we present the results of a multidisciplinary study carried out on the Dedication wall mosaic, realized by a byzantine workshop in the 12th century in the Church of St. Mary of the Admiral in Palermo, and where numerous black-appearing tesserae, supposed to be composed of obsidian by naked-eyes observation, are present. Historical documents, multispectral imaging of the wall mosaic, and some analytical methods (SEM-EDS and XRPD) applied to a sample of black tesserae, concur in identifying here the presence of obsidian and different obsidian-like glass tesserae. This evidence, although related to the apparent tampering and restoration, could open a new scenario in the use of obsidian and obsidian-like glass tesserae during the Byzantine period in Sicily and in the reconstruction of multiple restoration phases carried out between 12th and 20th century AD on the mosaics of St. Mary of the Admiral.

Highlights

The Dedication wall mosaic (Figure 1) decorates the eastern wall of a northern baroque chapel, partially demolished in the 19th century, inside the church of St
The time-lapse analysis of the pictures in a frame of around a hundred years helps in the identification of several significative anomalies
The Virgin face in this mosaic appears similar to this, contemporary, of the Virgin in the Nativity scene at the Palatine Chapel (Brenk, 2010, p. 460), but with only this information we cannot have any certainty about this originality

Summary

Introduction

The Dedication wall mosaic (Figure 1) decorates the eastern wall of a northern baroque chapel, partially demolished in the 19th century, inside the church of St. Mary of the Admiral in Palermo (Figure 2 and Figure 3). The mosaic represents the Admiral George of Antioch in proskynesis, at the foot of the Virgin Mary. The Mother of God, Μητέρα του Θεού in Greek, as in the abbreviation ΜΡ ΘΥ, is praying for her son Jesus Christ, shown in the right upper corner of the same scene. The Virgin Mary holds in the left hand a long white sheet reporting the text of her prayer made with glittering dark tesserae. Pointing at George, she asks Jesus Christ for the forgiveness of his sins because he built her this beautiful temple Pointing at George, she asks Jesus Christ for the forgiveness of his sins because he built her this beautiful temple (Kitzinger, 1990, pp. 316–17)

Methods

Results

Conclusion