Each of these sherds belongs to a number of highly important groups of glass testifying to the various productions of glass within the early Islamic lands.
The piece of sandwich glass is the earliest and most rare example in this group. The technique, which was first used by the Romans (circa fourth century AD) 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 as can be seen along the edges of the piece.
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.221-2); a bottle in the British Museum (inv. no. 1978.10-11.2) (ibid, no.111, pp.223-4); and a stemless cup in the Corning Museum of Glass (inv. no.64.1.32) (ibid, no.112, p.225). All bear similar decorative patterns to the present example suggesting a common timeframe and centre of production.
Continuing chronologically, the seven examples of mosaic or millefiori glass bear witness to the persistence of this technique in Syria and Iraq in the early Islamic period after its flourishing in the Hellenistic and Roman times. The widest and most varied group present are from the Mamluk period, and feature multiple decorative techniques, including lustre, applied gold and enamel. The dark purple fragment which at first appears mysterious, can be attributed to Syria or the Egyptian region, mid-late thirteenth century, following Stefano Carboni's cataloguing of an identical piece in the Al-Sabah Collection, Kuwait (Carboni 2001, pp.348-9, no.94e).