the Christ Deesis Mosaic in Hagia Sophia

the Christ Deesis Mosaic in Hagia Sophia

Probes beneath the surface of the existing mosaic and cornice show that there was an earlier mosaic in the spot now occupied by the great Deesis. A number of gold tesserae made of darker glass were found beneath the cornice and these appear to be of sixth century manufacture.

The Deesis must have been completed in one summer season, from May - September, since there were two undercoats of plaster that had to dry before the final layer was applied on which the mosaic was set. The two under-layers were pretty straightforward. The first layer contained crushed brick, lime dust and chopped straw. The second layer was finer and upon this layer rough outline of the design of the mosaic was painted. The plaster on the Deesis panel was finely done with large trowels and has some variation in it on purpose. A slightly uneven surface would reflect gold mosaic in a lively, glittering way. When Justinian built the church in the sixth century the plaster work was fast and a bit sloppy - they had huge areas to cover - imagine the vast vaults to be done - in gold mosaic and not much time to get it finished. The uneven surfaces and joins of Justinian's time have given those mosaics a much admired, but unintended shimmer. It was much easier to lay plaster on a flat surface and fortunately, that's what our workmen had to cover here in the south gallery.

The same plastering method is found in Byzantine churches from Greece to Italy, Russia and Georgia. This technique remained the same for almost 800 years, until the end of the empire.

Before the mosaic artists began work, a huge number or mosaic tesserae had to be assembled in various colors according to hue and intensity of color. Each color might which require dozens of shades. Some mosaic was stone and other was glass. The stone tesserae included cubes of semi-precious stones, such as lapis lazuli and porphyry. However, it was the glass tesserae that had the strongest and most brilliant color combined with the subtle effects on light penetrating the cubes. A significant amount of the gold glass was from the 6th century and was 500 years old. The tones of gold ranged from deep yellow to a sun yellow and in many cases include what appears to be red gold and white gold. These variations are caused by the various colors of glass under which the gold leaf is laid, by the gold used, and sometimes by paint applied under the tesserae. In the background of the Deesis, silver is also found. Great care was taken with the selection of the gold. Our artists were experts at using various types of gold tesserae to create dazzling effects.

Byzantium was still one of the world-centers of glass production and its factories could produce tons of mosaic a year, which was exported throughout the empire, Western Europe and the Middle East.

Once the plaster had dried and set properly, work began on the topmost layer of lime and marble dust where the mosaic cubes would be set. This fine layer of plaster was applied in a patchwork of sections just large enough to be completed in one day's work. The plaster joins were easy for the restorers to see and record. It gave them a good understanding of how the mosaic was created. On this layer a detailed colored painting was prepared as a guide for the artists.