The final stage of mosaic-glass production is relatively simple: the tiny tesserae are arranged according to a desired pattern one by one over a heat-resistant form that gives shape to the object. It is then placed in a kiln at high temperature to fuse their edges, thus creating a single piece, and left to cool down slowly. After polishing, the work is complete.
The preparatory stage, however, is extremely time-consuming because each tessera represents a diminutive slice from a long and narrow glass cane that was originally formed by wrapping layers of different-colored glass around its core until the desired combination was achieved. The finished cane probably had a diameter of three to four inches (7.5–10 cm) and was at least fifteen to twenty inches long (35–50 cm). In order to reduce it to the desired diameter of about one-tenth of an inch (2.5 mm), the cane was softened and pulled from both ends, maintaining the original cross-section pattern; once the cane had cooled, it was cut into thin slices. Initially made of simple patterns of concentric circles or bicolored spirals, by late Roman times canes began to include more complex and ambitious designs. Islamic glassmakers inherited the canemaking technique, improving upon it in late eighth- or early ninth-century Abbasid Iraq.
Inevitably, glass-mosaic vessels were destined to be small in size with simple open shapes not only due to the complexity of the technique but also because they were slumped over a mold and could not be blown to a larger size. The present bowl, with a diameter of almost six inches (15 cm), seems to represent the largest intact work in this technique. When viewed through transmitted light, the bowl comes alive because the fused outer edge of each slice is a translucent emerald green.
First created in imitation of variegated stones such as agates, mosaic glass acquired a more ornamental function in the Islamic period. We know, for example, that the floor in front of the throne of the Abbasid caliph in Samarra was composed of multicolored, flowerlike mosaic tiles. Venetian glassmakers, who revived the technique, which became known as millefiori or "a thousand flowers" in Europe during the fifteenth century, were able to use it to create blown vessels.
Stefano Carboni in [Ekhtiar, Soucek, Canby, and Haidar 2011]
1. A photographic demonstration of the various phases of canemaking, fusing, and slumping performed by William Gudenrath of the Corning Museum of Glass can be found in Carboni et al 2001, pp. 58–59.
2. The largest surviving fragment of these tiles is in the Museum für Islamische Kunst, Staatliche Museen zu Berlin. For a color image that fully suggests the original dazzling effect of mosaic glass, see ibid., p. 148, no. 61.
[ Mansour Gallery, London, until 2001; sold to MMA]
New York. The Metropolitan Museum of Art. "Glass of the Sultans," October 2, 2001–January 13, 2002, not in catalogue.
Metropolitan Museum of Art Bulletin vol. 59 (2000–2001). pp. 14-15, ill. (color).
Carboni, Stefano, David Whitehouse, Robert H. Brill, and William Gudenrath. Glass of the Sultans. New Haven: Yale University Press, 2001. pp. 58–59.
Journal of Glass Studies 44 (2002). p. 217, ill. (b/w).
Ekhtiar, Maryam, Sheila R. Canby, Navina Haidar, and Priscilla P. Soucek, ed. Masterpieces from the Department of Islamic Art in The Metropolitan Museum of Art. 1st ed. ed. New York: The Metropolitan Museum of Art, 2011. no. 15, p. 38, ill. p. 38 (color).