Probes beneath the surface of the existing mosaic and cornice showed that there had been an earlier mosaic in the spot now occupied by the great Deesis. A number of gold tesselae made of darker glass were found beneath the cornice and these appear to be of 6th century date.

Our mosaic must have been completed in one summer season, from May - September, since it was only practical to be laying plaster during this drier period of the year. To prepare for the mosaic special workmen were engaged to preparing the wall. These men applied three layers of plaster down on the underlying brick and stonework. The first layer was the most course and 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.

Once this 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. On this layer a detailed painting showing the figures with coloring was applied on it in fresco.

Many Byzantine paintings and mosaics were done with stenciuls made from other works. This ensured that each ikon was true to it's prototype and could be trusted to be a true representation of the saint depicted. In some cases a great and rare artist could work right on the plaster without stencils and preparatory drawings - but this was very rare and discouraged among artists.

The background of the panel is laid in a three-lobed motif and many of the gold tessellae are set at an angle. The background would have been laid by lessor artists and apprentices in the mosaic attelier after the faces, halos and garments of the saints had been completed by the masters.

There is an obvious difference in the level of detail applied to the backgrounds and other parts of the mosaic. One can easily see a stepping up in the number of tessallae used per square inch from the garments to the hair, hands and faces. Indeed, the faces are laid in a painterly fashion with brushstroke-like lines ending in arrow-shapped slivers of glass and stone.

How much work could be done in a day? Careful examination of the setting bed clearly reveals the seams of each day's work. Along these edges cubes are more likely to drop away, leaving trails of missing tessalae where patches of plaster adjoin one another.

From this observation it appears from the plaster that the face, neck and beard of Christ were done in one session and the hair in a separate one. The clothing and throne would have gone faster but there was a larger area to cover. Where one would have expected a simplification in the laying of the mosaic in the garments this is only true to an extent. The clothing contains a myriad of colors and patterns that show the same level of bravura technique as the faces. Every inch of this mosaic shows a high degree of sophistication and pride in workmanship. Many of the details would have been invisible to the spectator and only seen up close. The artists working on the panel were either working for their own self-gratification or to please God, probably both.

In preparation for the mosaic a huge number of tessallae in various colors would have been organized according to hue and intensity of color. The cubes used included gilded tessallae covered with transparent glass, dyed glass in a variety of colors, various colored stones and marbles in various shades of white and brown, and even cubes of semi-precious stones, such as Lapis Lazuli. Many cubes were salvaged from disassembled mosaics in derelic and abandoned Byzantine churches. In the great Deesis panel there are also found many rare and unique colors such as violet, blue and vermillion in glass which show the importance of this Imperial commission.

After the work was completed it became a place of special adoration of Christ. The marble floor shows the footprint of a low chancel-like enclosure and the marks of a large candle stand. If the mosaic pre-dated the Latin conquest of 1204 - as I believe it does - the mosaic must have made a huge impression on the Crusaders. Directly across from the mosaic a Venetian Doge had his tomb installed.

During the late Byzantine period the mosaic was carefully mantained and it shows places where minor repairs were made with cubes set in beeswax. It is also thought that at some point in time the bottom of the mosaic became damaged and a layer of marble panels was set along the bottom of the panel to conceal this.