The Composition of Byzantine Glass Mosaic Tesserae

International Network Sponsored by
The Leverhulme Trust 2007-2010

Mosaics are perhaps the most outstanding examples of Byzantine art which survive, yet we know next to nothing about how they were made. One of the most important gaps in the study of Byzantine mosaics lies in our understanding of the manufacture of the medium of their composition. Glass-making was a relatively sophisticated skill in the mediaeval world, yet no written documents survive from Byzantium about the methods used for making a mosaic or creating its tesserae, and we have no knowledge of the ways in which manufacturing patterns existed and changed over time, or, indeed, of where and exactly how tesserae were created. Only the mosaics themselves speak to their composition. We know that glass making and glass working were two distinct processes, but did the differently coloured glass tesserae on one site all come from the same batch of raw glass? Where did that raw glass come from? The nature of the actual colours used in making mosaics changed over time: is this simply a question of changing aesthetics or are there also technical explanations for these alterations?

To discuss questions like these, we are running a series of workshops. We hope that these will not only provide answers to central questions about artistic practices, but will also feed both information and analysis into wider debates about the nature of trade and exchange within the Mediterranean during this period and into our understanding of political and social changes within the Mediterranean world. From a study of the distribution patterns of glass tesserae, can we, for example, gain any sense of how the sourcing of raw materials for glass-making changed over time? One thing we are particularly keen to explore is the possibility of collating evidence about the chemical make-up of glass tesserae, which might then make it possible to build up a pattern of both mosaic and glass manufacture within the Mediterranean throughout the Middle Ages.

It is a project that can only be accomplished with collaboration across disciplines and scholars: no single person has the tremendous breadth of knowledge that would be required to tackle this field alone. Consequently, the network, which cuts across art history, archaeology, chemistry, physics and Byzantine studies, brings together a range of scholars from Europe and America interested in the chemical and physical analysis of Byzantine glass together with those concerned with the formal and cultural aspects of Byzantine mosaics in order to reappraise mosaics and mosaic making in this interdisciplinary context. The programme aims to draw together scholars who work on different aspects of glass mosaic production and analysis from the scientific and art historic worlds, but who rarely, if ever, meet and discuss their common concerns.

Workshops during 2007-2010 in London, Ravenna, Athens and Thessaloniki will address technical questions about the manufacture and distribution of coloured glass mosaic tesserae. One of the key objectives is to establish a common framework for the testing of glass and the comparison of the scientific data obtained from testing. Another is to set up a centralised record of information of this nature, in order to facilitate its comparison. The workshops will also discuss questions beyond the purely technical. In particular, they will address issues of whether patterns occur in the distribution and colours of Byzantine mosaic glass. By collating evidence it should become possible to build up a pattern of mosaic and, further, glass manufacture within the Mediterranean throughout the Middle Ages.

We are grateful to The Leverhulme Trust for undertaking the funding of this International Network.

The Project is directed from Sussex by Prof. Liz James (Department of Art History, University of Sussex and Sussex Centre for Byzantine Cultural History).

For further information visit our website.

See also Liz James's excellent 2006 paper Byzantine glass tesserae.

The Network is housed in the Sussex Centre for Byzantine Cultural History at the University of Sussex. If you are interested in joining the Network or want more information please contact Liz James (01273 873611) or Network Facilitator Bente Bjornholt (01237 873038).