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Uranium glass

Uranium glass is glass which has had uranium, usually in oxide diuranate form, added to a glass mix prior to melting. The proportion usually varies from trace levels to about 2% by weight uranium, although some 19th-century pieces were made with up to 25% uranium.

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. Otherwise, modern uranium glass is now mainly limited to small objects like beads or marbles as scientific or decorative novelties.

Appearance

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.

Vaseline glass

The most typical color of uranium glass is pale yellowish-green, which in the 1920s led to the nickname vaseline glass based on a perceived resemblance to the appearance of petroleum jelly as formulated and commercially sold at that time. Specialized collectors still define "vaseline glass" as transparent or semitransparent uranium glass in this specific color.

"Vaseline glass" is now frequently used as a synonym for any uranium glass, especially in the United States, but this usage is not universal. The term is sometimes carelessly applied to other types of glass based on certain aspects of their superficial appearance in normal light, regardless of actual uranium content which requires a blacklight test to verify the characteristic green fluorescence.

In England and Australia, the term "vaseline glass" can be used to refer to any type of translucent glass. Even within the United States, the "vaseline" description is sometimes applied to any type of translucent glass with a greasy-looking surface lustre.

Other colors

Several other common subtypes of uranium glass have their own nicknames: custard glass (opaque or semiopaque pale yellow), jadite glass (opaque or semiopaque pale green; initially, the name was trademarked as "Jadite", although this is sometimes overcorrected in modern usage to "jadeite"), and Depression glass (transparent or semitransparent pale green).

However, like "vaseline", the terms "custard" and "jad(e)ite" are often applied on the basis of superficial appearance rather than uranium content. Similarly, Depression glass is also a general description for any piece of glassware manufactured during the Great Depression regardless of appearance or formula.

History

Pre-industrial usage

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..

Martin Klaproth (1743-1817), the discoverer of uranium, later experimented with the use of this element as a glass colorant.

19th-century mass production

Uranium glass became popular in the mid 19th century. The first major producer of items made of uranium glass is commonly recognized as Josef Riedel, who named the yellow (Gelb) and yellow-green (German: Gelb-Grün) varieties of the glass "annagelb" and "annagrün", respectively, in honor of his wife Anna Maria. Riedel was a prolific blower of uranium glass in Dolni Polubny, Bohemia from 1830 to 1848.

By the 1840s many other glassworks throughout Europe began to produce uranium glass items, including new varieties of uranium glass. The Baccarat glassworks of France created an opaque green uranium glass which they named chrysoprase, for its similarity to the green form of chalcedony with that name.

At the end of the 19th century, it was discovered that uranium glass with certain additional minerals could be tempered at high temperature to partially crystallise, changing from its normal transparent yellow or yellow-green with increasing opacity to, ultimately, opaque white. This material, technically a glass-ceramic, inspired the name "vaseline glass" due to its similar appearance to petroleum jelly.