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).