This blue vase is a masterpiece of the so-called “cameo” technique. The production of cameo vases has been dated between 25 B.C. and 50 A.D. These dark blue, almost black vessels have a transparent neck and an outer coating of white opaque glass where an engraver (the diatretarius) would carve a decorative motif. According to scholars, cameo glass was made following this procedure: in order to bind the two layers of glass, the craftsman cast a layer of glass into the receptacle-shaped mould which formed the vessel's exterior. Then, using a blowpipe, he took molten glass from the furnace and blew it into the mould, taking care to make it adhere to the previously cast shape. In order to made the two layers of glass perfectly adhered, without risks of breaking, the glassmaker had to have a precise knowledge of the proportions of the two pastes.