Lustre painting was executed usually on colourless, more rarely on manganese purple, glass. There are a very few examples of lustre painting on blue glass (Lamm 43:5 and 6, both painted in orange lustre). Painting in two or more tones of lustre as here is characteristic of the 8th-10th century; in the Fatimid period painting was restricted to a single tone. Painting on both sides of the glass was the common practice in the earlier period.
The decoration of this fragment is that of the polychrome lustre painted pottery of Samarra (Philon, p.83, fig.151). This adds greatly to its importance since it supports the historical sources that Basra supplied Samarra with glass which would probably have included lustre decorated glass. Most of the surviving examples of lustre painted glass were made in Egypt or Syria.

Lamm, J.:Mittelalterlicher Gläser und Steinschnittarbeiten aus dem Nahen Osten, Berlin 1929-30
Philon, H.: Early Islamic Ceramics: Benaki Museum, Athens, London, 1980