An exceptionally rare "sandwich glass" cup, Syria, 9th-10th century

the transparent glass of cylindrical form with flat base with pontil, decorated with gold and blue enamels sandwiched between two layers of glass, with an arcade of palmettes below a minor band of split-palmettes juxtaposed by blue dots, the base with a bird motif

Sandwich glass is extremely rare in the Islamic period. The technique, which was first used by the Romans (circa 4th century A.D.) and went on to be developed by the Byzantines, involves sandwiching a gold-leaf decorative pattern between two layers of glass. In this particular example, the gold leaf has been applied to the glass on the inside after which a second layer of glass has been blown into the first. 

Carboni writes: "The technique was probably first invented to meet the need for luxury glass objects incorporating gold.  Had the gold leaf been applied to the exterior surface of a vessel, the decoration would have lasted for a short period, even after firing.  The idea of encapsulating it between two layers of colourless glass that would reveal the pattern and at the same time preserve it represented a clever artistic solution.

"In the Islamic period, the production of sandwich glass probably arose from the challenge of imitating Roman examples than from the need to preserve the decoration for posterity. The technique was limited and short-lived, judging from the rare examples and fragments, none of which bears an inscription that would link the group to a specific court or period.  Obviously a luxury item, sandwich glass was therefore more probably the result of experimentation in an established glass centre rather than of caliph or courtly patronage, although the expense involved in its production made it affordable only to the wealthy." (Carboni and Whitehouse 2001, pp.221-222).

There are only a handful of surviving examples located in major public collections: a fragmentary cup in the David Collection (inv. no.4/1987) (von Folsach 2001, p.213, no.325; Carboni and Whitehouse 2001, no.110, pp.221-222); a bottle in the British Museum (inv. no. 1978.10-11.2) (ibid., no.111, pp.223-224); and a stemless cup in the Corning Museum of Glass (inv. no.64.1.32) (ibid., no.112, pp.225).  All bear similar decorative patterns to the present example suggesting a common timeframe and centre of production.