as sketched in E; it is further whetted off at F, opened, as G, and has the projecting canes on the outside of the cup; a Glass disk, or post, being made to adhere to its open end, as H. The inner case of the Vitro di Trino process is thus completed. To make a corresponding outer case, a ball must be formed into a cup or cover, of exactly the same character, a little larger, but turned inside out, as I; which gives the twist the reverse way, and causes its interior canes to project inside the cup, K.

The inner cup, or case, H is now placed within the outer case, K; and these two conical cases now crossing each other, are, by re-warming, collapsed together, entrapping between each white enamel crossed section, uniform interior air-bubbles, as L; and the two cases, now become one, may be formed into the bowl of a wine-glass, or any other vessel; the disk, H, having been previously removed by a gentle tap of the chest-knife. Upon this principle was made the specimen, in the coloured Plate 4, fig. 1.

The principle of casing a layer of colour upon Flint Crystal Glass, or as many layers or varieties of colour upon each other as may be required, was well known to the ancients who made the Portland and Naples Vases. Only one operation need be explained, as every additional coating is merely a repetition of the same process. Presuming, therefore, that any two or more glasses intended for casing have been mixed of the same specific gravity, to give them the capability of harmonizing,—that is, contracting and expanding equally,—the blower has to gather a ball of solid Glass, intended for the interior layer, in the usual manner, as A, which, in this instance,