Hagia Sophia Mosaics
Tons of gold are used in the construction of Hagia Sophia mosaics however besides the gold, stone pieces such as silver, tinted glass, terracotta and colored marble also have been used. In the year of 726 all icons and statues had been removed from the Hagia Sophia with the destruction order of Leon III. This is why all of the mosaics that contain face depictions which you can see today are the mosaics that had been made after the period of iconoclasm. In addition to these some of the mosaics which does not contain any face depictions are the first mosaics that had been placed in Hagia Sophia in the sixth century.
Right after Hagia Sophia converted into mosque in the year of 1453, mosaics that coated with a thin plaster due to they contain human figures and left under this plaster for centuries were able to get rid of the natural and man-made destruction. It can be understood that mosaics that do not contain any human figure and some of the mosaics that contain human figures are left without coating with a plaster in line with the reports of explorers that visited Istanbul during the 17th century and watched the conversion of Hagia Sophia from church to mosque. Fully coating of the mosaics in Hagia Sophia took place in 842 or towards the end of 18th century. Baron De Tott who visited Istanbul in 1755 noted that all of the mosaics were coated with a plaster.
Fossati brothers who engaged in a variety of restoration work in the Hagia Sophia between 1847 and 1849 at the request of Sultan Abdulmecid and took permission for the documentation of mosaics that can be found during the restoration removed the plaster on the mosaics, copied the designs of the mosaics and then closed the plaster again. These documents are missing today. Whereas architect W. Salzenberg who sent by German government for the restoration work in that year drew some of the patterns of mosaics and published them.
Most of plaster on the Hagia Sophia mosaics were removed by a team of organization named Byzantine Institute of America during 1930s. This took place for the first time in 1932 by the head of the Byzantine Institute of America institution, Thomas Whittemore, and the first mosaic that revealed was the mosaic that is on the Emperor Gate.In addition to these it is possible to see the mosiacs on the half dome in the eastern side.