Mid-century trilateral controlled-bubble sommerso glass vase from the Theresienthal  glassworks, Germany c1960's. The vase is of trilateral form and of sommerso style with thick clear crystal encasing a green core. Decorated with a delicate spiral of bubbles. Ground pontil mark. The vase measures 21 cm in height, 8.5 cm in width and 8 cm depth.
 
Often called “controlled bubble glass” but also “bullicante” – this artisan technique was especially popular with Murano as well as Scandinavian glass artists during the 1950s and 60s. During the glass-blowing process, indentations are made on the surface of a molten “portion” of glass that is malleable. Because molten glass retains its shape for a time, when the outer casing layer of glass is applied, air bubbles become trapped between the two layers. The pattern of bubbles is dependent on the pattern in which the indentations are first made as well as in how the glassblower then manipulates the molten glass. Patterned indentations are usually made by rolling the glass portion on a surface with spikes or pressing it into a conical mould with spikes on its inside. Single or multiple bubbles can also made using a hand tool to make indentations before applying the outer layer. Bubbles can also be made by adding certain substances to the glass that will release gas during the process however these will not form in a pattern.