Cobalt blue glass. A remarkable example of early cast ribbed bowls, this piece was made using a saturated hue of cobalt blue glass. This type of vessel was created by a process of sagging, lathe-cutting and fire polishing. of extremely compact form, the bowl has a very slightly concave bottom, a curving body with a series of vertical ribs and a vertical rim with rounded edge.
Although these bowls were quite popular in the first centuries BC/AD, the most frequently encountered specimens are in bluish-green glass. Pieces in colored glass, particularly such a rich dark blue, are extremely rare and seldom offered.
Cf: Oppenlander, no. 253, pp. 96 & 99; Toledo 1989, nos. 235 & 238, pp. 265-266. For a discussion of the complex process involved in making such vessels, see Toledo 1989, pp. 244 ff; The National Archeological Museum of Naples, Stefano De Caro, 1996.