We have some stunning glass pieces at the moment, some of which are a beautiful green uranium glass. To the general public the word uranium is synonymous with nuclear weapons, nuclear power stations and radioactivity. But the term uranium glass, to the collector, will always be associated with that yellow, green, transparent glass which glows vibrantly under a black, or UV, light.
Uranium glass is a coloured glass, made by adding a small amount of uranium into a base glass. It has a typical colour tone, either light yellow or light green. The glass has a unique and beautiful shine due to the fluorescent effect of uranium contained in the glass. Uranium glass has been sought after for more than 200 years. The radioactivity of uranium glass has been well researched and it has been found to be about the same level naturally contained in the human body.
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. Most such objects are now considered antiques or retro-era collectibles, although there has been a minor revival in art glassware. 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.
But who first thought of using uranium to colour glass? The use of uranium glass dates back to at least 79 AD, the date of a mosaic containing yellow glass with 1% uranium oxide found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy by R. T. Gunther of the University of Oxford in 1912. Starting in the late Middle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic) and was used as a coloring agent in the local glassmaking industry. Some authors give the honour to Josef Riedel at his glassworks in Bohemia in the 1830s. It may be that he was the first to produce uranium coloured glass in quantity with his Annagrun and Annagelb – green and yellow glasses named after his wife – but it is unlikely that he was the first to add Klaproth’s discovery to sand and alkali. We know from records held by the Museum of London that Whitefriars used uranium colouring in 1836. There is good reason to believe that the British scientist, William Vernon Harcourt, started experimenting with glass compositions in 1834. He did not publish his work but it would appear that by 1861 his work had included uranium. There are reports of a uranium glass beaker cut with a portrait of the famous German poet and dramatist Friedrich Schiller. He died in 1805 and it is thought this beaker commemorates the 20th anniversary of his death, as it is inscribed with the date 1825. Between 1800 and 1809, Thomas Cock, brother-in-law of P.N. Johnson of Johnson Matthey, working at the laboratory of William Allen at Plough Court in Lombard Street, studied the extraction of uranium oxide and its application to the colouring of glass. An early English reference to uranium in glass also comes from C. S. Gilbert’s Historical Survey of Cornwall (1817). From all this we conclude that the colouring properties of uranium were known early in the 19th century, but it was not until the second quarter of the century that it was marketed