A fragmentary dish of the same shape, in cobalt-blue, with the addition of diamond-cut decoration was excavated at Nishapur (Jens Kröger, Nishapur: Glass of the Early Islamic Period, New York, 1985, no.164, pp.117-18). Although the very strong large-scale geometric decoration on this dish is harder to parallel, a related blue glass dish, remarkably offered en suite with a conical blue bowl, was sold in these Rooms, 12 October 1999, lot 322. Another dish sold at Bonham's, 12 April 2000, lot 138.
The diamond-cut fragmentary dish mentioned above (Kröger, op.cit., no.164) has similar companion pieces found in the Famen temple in China which dates them very specifically to before 874. In the Chinese temple six dishes on small pedestal feet with slightly splayed rim have been preserved, all of (dark) blue glass (Stefano Carboni, Glass from Islamic Lands, London, 2001, p.72). The late 9th century date would also be corroborated by the shape of the bowl here, with its very close profile to the pottery of Nishapur traditionally dated to the 10th century (see for example Charles K. Wilkinson, Nishapur. Pottery of the Early Islamic Period, New York, 1974, no.18, p.97).