A unique minai-decorated glass base sherd, Kashan, Persia, circa 1200

the greenish thick-walled glass with rounded bottom, decorated in  the centre with a roundel painted in cold-fired enamels with a central elevated figure seated on a throne flanked by musicians playing stringed instruments with a chained leonine creature lying at the feet of the enthroned figure, black, white and coloured enamels and traces of gilding 

The technology of glassmaking and glazed pottery production are closely linked and glassmakers and potters frequently exchanged ideas and techniques. The use of overglaze enamels was widespread in pottery production at Kashan in the late 12th and early 13th centuries, particularly prior to the Mongol invasions of the 1220s. The fact that the technology of cold-fired enamels was not used by the glassmakers as well, is one of the great mysteries of medieval Persian glass manufacturing. 

The existence of this glass base sherd, a solitary survivor, tells us that not only was the technique experimented with by the glassmakers but also that it never caught on, for if it had, surely more fragments would have survived.

A scientific analysis on the glass carried out by CIRAM confirmed that the chemical composition and micro-structure of the corroded glass result from natural and long-term processes and that the raw material of the glass matrix and the lead white pigment are consistent with a 12/13th century date.