The Strolling through Istanbul guide wrote that the “mosque is darkened by the soot which has accumulated on its windows” and that “the tiles which decorate the interior are of a quality inferior to those in earlier mosques, the celebrated Iznik tiles of the period 1555-1620”. Still they have one group of these tiles, representing Mecca, that is considered so valuable it is locked in as if it were gold (as a matter of fact, gold is just a metal, an Iznik tile can be more valuable, being a piece of art that cannot be replaced the way you can buy an ingot of gold).

İznik work, named after the town in western Anatolia where it was made, is a decorated ceramic that was produced from the last quarter of the 15th century until the end of the 17th century. Often used motifs are tulips, roses, carnations, hyacinths, violets, pomegranates, feather-shaped reed grass, leaves, grape bunches and vines, and arched flower branches. In Ottoman culture (and more generally in Islamic art) flowers symbolize the Garden of Eden and Paradise.

İznik town was an established centre for the production of simple earthenware pottery with an underglaze decoration when in the last quarter of the 15th century, craftsmen in the town began to manufacture high quality tiles and pottery with a fritware body (frit being added to clay to reduce its fusion temperature), painted with cobalt blue under a colourless lead glaze. During the 16th century the decoration gradually changed in style, becoming looser and more flowing. Additional colours were introduced. Initially turquoise was combined with the dark shade of cobalt blue and then the pastel shades of sage green and pale purple were added. Finally, in the middle of the 16th century, a very characteristic bole red replaced the purple and a bright emerald green replaced the sage green.
From the last quarter of the 16th century there was a marked deterioration in quality and although production continued during the 17th century the designs became poor, and the city's role as primary ceramics producer was taken up by Kütahya.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Guides Bleus: Turquie’ – Edition 1986 & Wikipedia.