Concept
Uranium glass is glass which has had uranium, usually in oxide diuranate form, added to a glass mix before melting for colouration. The proportion usually varies from trace levels to about 2% uranium by weight, although some 20th-century pieces were made with up to 25% uranium. First identified in 1789 by a German chemist, uranium was soon being added to decorative glass for its fluorescent effect. James Powell’s Whitefriars glass company in London, England, was one of the first to market the glowing glass, but other manufacturers soon realised its sales potential and Uranium glass was produced across Europe and later North America. Uranium glass was once made into tableware and household items, but fell out of widespread use when the availability of uranium to most industries was sharply curtailed during the Cold War in the 1940s to 1990s. Most such objects are now considered antiques or retro-era collectibles, although there has been a minor revival in art glassware. Otherwise, modern uranium glass is now mainly limited to small objects like beads or marbles as scientific or decorative novelties. The normal colour of uranium glass ranges from yellow to green depending on the oxidation state and concentration of the metal ions, although this may be altered by the addition of other elements as glass colorants. Uranium glass also fluoresces bright green under ultraviolet light and can register above background radiation on a sufficiently sensitive Geiger counter, although most pieces of uranium glass are considered to be harmless and only negligibly radioactive. File:Uranium glass beads, black background.jpg|Modern uranium glass beads (black background) File:Uranium glass beads, UV light.jpg|Modern uranium glass beads (UV light) The most common color of uranium glass is pale yellowish-green, which in the 1930s led to the nickname "Vaseline glass", based on a perceived resemblance to the appearance of Vaseline-brand petroleum jelly as formulated at that time.