Byzantine mosaics: some practical considerations

The author examines what can be deduced from Byzantine wall and vault mosaics about the organisation and technique of their production. Medieval mosaics are better visible from a distance than post-medieval ones because the craftsmen employed clear, often dark, contours rather than striving for painterly effects. They also exploited the reflective qualities of millions of glass tesserae set at slightly different angles, and they appreciated that mosaic works best on curving surfaces. They also adapted the shading and composition of their images to make use of external sources of light. In regard to materials, coloured glass was difficult to manufacture, especially red glass, so mosaics with a lot of red (or silver or gold, which were produced by sandwiching a thin sheet of the metal between two layers of glass) would have cost more than those employing only transparent blues and greens. Regarding transport, shipwrecks reveal that there was a substantial trade in raw and second-hand glass, and some written sources refer to the export of tesserae from Byzantium to cities in the Near East and Spain. Mosaic decoration on a large scale involved considerable financial investment and organisation. None the less there is evidence for widespread production of wall and vault mosaics, even in minor and remote cities. Much remains to be done on the chemical analysis of glass tesserae, to see whether there were variations according to date and place, and thus better understand the processes of production and distribution.