After 160 years of darkness, Seraphim's face is in daylight.
There are 4 seraphim mosaics ( God's protector angels with 6 wings) on the 4 pendentives that carry the dome. The 4 seraphims' faces were covered with 6-7 layers of plaster for almost 160 years during the sovereignty of Ottomans. The last person who saw the faces of the Seraphims was the Swiss architect Gaspare Fossati while he was holding the restoration at Hagia Sophia in 1840s. With a 10 day hard work, experts managed to take off the 7 layers of plasters and reveal the face of one of the seraphims.