Iznik is the Ottoman name of the ancient Byzantine capital, Nicaea, and has always flourished due to its position on one of the main trade routes across Anatolia to the East. It was one of the first places occupied by the emerging Ottoman dynasty in the late C13th. There is no documentary evidence (before a palace kitchen register dating 1489-90) for the pottery which we now come to identify with this town, so we have no clear idea of when production of the new white fritware developed; however, there was an older pottery tradition already flourishing at Iznik, so the late C15th court-sponsored expansion of the industry of this town, rather than another, is easily explicable: the ceramic tradition was already established and all the necessary infrastructure and materials, such as fresh water, fuel, clay and minerals for glazing compounds, were already there.

According to the evidence of the C17th English traveller, Dr John Covel, the right kind of clay was available close to Iznik; he visited the town in the 1670s, and remarked on its decrepitude compared to its splendid Byzantine past. He also describes the weekly Wednesday market, at which one could buy:

Recent excavations at Iznik have proved conclusively that it was the production centre of a well-known type of underglaze–painted earthenware called "Miletus ware", after the first discovery of this type at Miletus (on the coast of south-west Anatolia). This type of pottery has a reddish earthenware body covered with a white slip, which is then painted under its lead-alkali glaze in dark cobalt blue, sometimes purple, turquoise or green; it averages 25 cm in diameter. Many pieces of ‘Miletus ware’ are decorated with a central rosette, others with a cluster of spiralling leaves, flying birds, six-pointed stars, or interlocking arabesque panels filled with tiny spirals; a characteristic feature is the use of narrow radiating petals in the cavetto, which may take their inspiration from metalwork or, more likely, from Chinese celadons of the Yuan and early Ming dynasties, which are richly represented in the Topkapi Saray collection. Excavations at Iznik in 1985 even uncovered a Chinese celadon sherd.

Examples have been found at Iznik together with kiln debris, such as spurs used to separate the objects in the firing, providing evidence for Iznik as a major production site for this pottery type. Other types of earthenware also seem to have been made at Iznik: the sgraffiato- and slipware-decorated pottery which is found in so many centres across the Islamic world, as far afield as Nishapur and Samarkand. These were thus the immediate precursors of the new white fritware which developed sometime towards the end of the C15th, and they probably continued to be produced as popular local wares after that date.

The Iznik craftsmen must be credited for the major innovation which occurred with the establishment of the late C15th underglaze industry: the invention of a very finely textured quartz-frit body, close in chemical composition to that described by Abu'l-Qasim in 1301, with a low iron content and a finely-textured slip. The glaze frit contains lead oxide as well as soda, and tin oxide in solution producing a brilliant transparent glaze. Fifteenth-century pottery produced in Egypt, Syria and even Persia, in imitation of Chinese porcelain examples of the period, is technologically inferior to this new Iznik ware, nor is there any technical similarity with the tiles made at Edirne (Muradiye, Üç Serefeli); it is interesting, however, that recent analysis of sherds of C16th ware from both Iznik and Kütahya (including wasters of early blue-and-white from Kütahya) shows that these two sites shared a common technology, with some minor differences.

As for firing techniques, we know very little since the Iznik excavations have produced no firm evidence for the form or dimensions of the C16th kilns, since all examples that have been found are to do with the production of glazed red earthenware. We also have no knowledge of how the tiles and vessels were stacked, while we can tell that ‘Miletus ware’ vessels were supported and separated by spurs (since triple scars in the centre of dishes are quite often seen). It is usually suggested that the large size and open shape of the Iznik vessels required that they be fired inside saggars, or enclosed ‘boxes’ made of earthernware, so that they could be stacked inside the kiln but without jeopardising the costly decoration on the dishes. Tests on Iznik ware have concluded that the firing temperature was around 850-900°C, which is low compared with the usual earthenware temperature of 1060°C or stoneware temperature of 1280°C.