Among the first glasswares to appear in significant numbers on Roman sites in Italy are the immediately recognizable and brilliantly colored mosaic glass bowls, dishes, and cups of the late first century B.C. The manufacturing processes for these objects came to Italy with Hellenistic craftsmen from the eastern Mediterranean, and these objects retain stylistic similarities with their Hellenistic counterparts.
Mosaic glass objects were manufactured using a laborious and time-consuming technique. Multicolored canes of mosaic glass were created, then stretched to shrink the patterns and either cut across into small, circular pieces or lengthwise into strips. These were placed together to form a flat circle, heated until they fused, and the resulting disk was then sagged over or into a mold to give the object its shape. Almost all cast objects required polishing on their edges and interiors to smooth the imperfections caused by the manufacturing process; the exteriors usually did not require further polishing because the heat of the annealing furnace would create a shiny, “fire polished” surface. Despite the labor-intensive nature of the process, cast mosaic bowls were extremely popular and foreshadowed the appeal that blown glass was to have in Roman society.
Trentinella, Rosemarie. “Roman Mosaic and Network Glass.” In Heilbrunn Timeline of Art History. New York: The Metropolitan Museum of Art, 2000–. http://www.metmuseum.org/toah/hd/rmos/hd_rmos.htm (October 2003)
Oliver, Andrew, Jr. "Late Hellenistic Glass in the Metropolitan Museum." Journal of Glass Studies 9 (1967), pp. 13–33.
Oliver, Andrew, Jr. "Millefiori Glass in Classical Antiquity." Journal of Glass Studies 10 (1968), pp. 48–70.