One of Byzantium's greatest achievements was its sumptuous mosaics. With the rise of the Byzantine Empire from the 5th century onwards, centred on Byzantium (now Istanbul, Turkey), the art form took on new characteristics. These included Eastern influences in style and the use of special glass tesserae called smalti, manufactured in northern Italy. These were made from thick sheets of coloured glass. Smalti have a rough surface and contain tiny air bubbles. They are sometimes backed with reflective silver or gold leaf.
The art of creating mosaic patterns grew and developed with the rise of the Byzantine Empire in the 5th century. New characteristics appeared in mosaics with Eastern influences in style and the use of glass tesserae, known as smalti, sourced from northern Italy. This added new texture and life to the mosaic patterns being created, with the smalti, which were cut from thick sheets of colored glass and had a rough surface and tiny air bubbles throughout, being backed by reflective silver or gold leaf.
Byzantine glass mosaic tile or smalti is the type of opaque glass tile used in classical Byzantine mosaics. Smalti is not molded into uniform shapes like modern glass mosaic tile.
Smalti is made by mixing glass and various minerals according to traditional recipes and melting the mixture in a furnace. The molten glass is then poured onto a slab for cooling, and then cut by hand into rectangular pieces. The pieces are about 1/2" or smaller and they aren't perfect rectangles. They vary in thickness, shape, size and color.
Mosaics made in Ravenna for the Ostrogoth king Theodoric are the first full manifestations of byzantine art in the west. As seen in two of the foremost works from his time, the baptistery of the arians and the church of Santís Apollinare Nuovo, the gold background now dominates. Accompanying it was silver, a novelty among the mosaics of Italy.
Also there were efforts made to uncover the Byzantine mosaics of Hagia Sophia(Ayasofia museum) Istanbul, Turkey. Restoration work in the 20th century was begun in 1932 by the American Byzantine Institute, during which most of the figures were uncovered.
Due to its long history as both a church and a mosque, a particular challenge arises in the restoration process. The Christian iconographic mosaics are being gradually uncovered. However, in order to do so, important, historic Islamic art would have to be destroyed. Restorers have attempted to maintain a balance between both Christian and Islamic cultures.