On the picture: The wall above the window in the southeast wall of the mihrab area.
The border in glazed tiles shows elegant calligraphy in which two scripts were used: kufic (in yellow) and sülüs (in white). The painted calligraphic works higher on the wall date from the 19th century, when the mosque was renovated after the 1855 Bursa earthquake.
In the upper half of the picture: Two colorful stained-glass windows in Classical Ottoman style, and the painted
prism-shaped triangles connecting the circular dome with the walls of the square mihrab area. This kind of wall paintings is called ‘kalem işi’ (= work of the pen/paintbrush), because it is inspired on the geometric or stylised ornamentation used by Ottoman calligraphers to illuminate books.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Vakıf Abideler ve eski Eserler’ - Vakıflar Genel Müdürlüğü III, Ankara 1983 .