Uranium glass is a type of glass that has had uranium added to it before melting to create colors

. The proportion of uranium in the glass usually varies from trace levels to about 2% uranium by weight, although some 20th-century pieces were made with up to 25% uranium

. Uranium glass was first identified in 1789 by a German chemist, and it was soon being added to decorative glass for its fluorescent effect

. The normal color 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

. 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