 Uranium glass is used as one of several intermediate glasses in what is known to scientific glass blowers as a 'graded seal'.This is typically used in glass-to-metal seals such as tungsten and molybdenum or nickel based alloys such as Kovar, as an intermediary glass between the metal sealing glass and lower expansion borosilicate glass.Uranium glass became popular in the mid-19th century, with its period of greatest popularity being from the 1880s to the 1920s.