In the Anatolian Seljuk period, glazed tile mosaic decoration was applied together with under-glazed tile panels we encounter in palaces, while in the Anatolian Turkic principalities of the 12th century, glazed tile mosaics were used, though not ubiquitously.

The Orhan Imaret in İznik is perhaps the first building in Ottoman architecture to be decorated with tiles. The lower part of the walls of the Imaret is covered with green and turquoise hexagonal tiles. The minaret of the Green Mosque, also built in İznik in 1378, is an example of the continuation of the Seljuk tradition with its mosaic tile and glazed brick technique, whose color range was further enriched. The tradition of mosaic tiles was continued in the Nilüfer Hatun Imaret, the mosque facade of the Bursa Murad II complex, and in various parts of the mosque and tomb in the Green complex, at times between bricks and at times between stones, and in such a way that the white plaster surfaces on the floor disappeared. The last applications of this technique in Istanbul during the reign of Sultan Mehmed the Conqueror can be seen in the outer Iwan of the Tiled Pavilion and in the tomb of Mahmut Pasha.

The most remarkable development in early Ottoman architectural ornamentation can be traced in the colored glazing technique, the most mature examples of which can be seen in the Green Tomb and the mosque in Bursa. It is known that craftsmen from Tabriz also worked on this complex of buildings, and Ali bin Ilyas Ali from Bursa, known as Nakkaş Ali, was responsible for the ornamentation program. The artist, who was brought to Samarkand by Timur, must have returned later. In the Green Complex, between 1421 and 1424, a diverse tile decoration program was successfully applied on the walls, mihrabs, ceilings of the cellars and Iwan ceilings and the sarcophagus, as well as on the raised and circular surfaces with floral folds. The matte red applied for the first time after kilning of the tiles according to the colored glaze technique, which separates the colors from each other with contours, draws attention as a kind of hardened paste. This color, which is understood to be crystallized mercury sulfide, later became the pioneer of the under-glaze raised red color in İznik tiles and ceramics.

The Green Complex, where various techniques were used in addition to the application of gold gilding on glaze on flat tiles, is a laboratory of Ottoman period Turkish tile art. Not only the extraordinary decoration quality of the tiles in the Green Tomb is remarkable, but also the combination of the dough that forms the substructure. In order to achieve good results on various surfaces, a special mixture was used, and the tiles, made with red paste obtained with free quartz and high silica ratio, were produced with a certain knowledge and experience. They were probably designed on site according to the ornamentation program and fired in local kilns. For the time being, it does not seem possible to evaluate the very small tile fragments found in the excavations in İznik, which point to the experimentation with colored glaze, to the extent of refuting this idea.

 After various examples such as the mihrab of the Muradiye Mosque in Edirne, the Yavuz Sultan Selim Tomb and Mosque in Istanbul dated 1522, and the mihrab of the Karaman Ibrahim Bey Imaret dated 1432, which is now exhibited in the Tiled Pavilion, the colored glaze technique produced perhaps its last magnificent examples in the 16th century in the Istanbul Şehzade Mehmed Tomb dated 1548 before giving way to the underglaze technique.

The first examples of tiles produced according to the underglaze technique of the early Ottoman period are found in the Muradiye tombs of Bursa. In these examples, blue-white decoration draws attention. In the 15th century, perhaps the most interesting blue-and-white decorated underglaze wall tiles can be seen in the Muradiye Mosque in Edirne. These hexagonal-shaped tiles, of which thirty-seven different examples have been identified, cover the lower part of the walls and are connected to each other by triangular flat plates.

From the first half of the 15th century onwards, İznik became prominent in the production of wall tiles as well as ceramics. The Seljuk combination of red paste scribing and slip painting techniques in ceramics began to transform into early Ottoman ceramics with white slip and free blue decoration, and the change in paste and decoration from the second half of the 15th century led to the development of a naturalistic style from the first half of the 16th century. While İznik played a crucial role in this period, recent research has proved that Kütahya also had a similar stylistic development with a different paste (‘Anadolu Toprağının Hazinesi Çini’ Belgin Demirsar Arlı-Ara Altun, pp.19-21).