Uranium glass

How to read it

Uranium glass has uranium added to the batch as a colorant. The Nuclear Regulatory Commission’s assessment of it, NUREG-1717 (2001), says the uranium ends up spread evenly through the glass as uranium oxide, an integral part of the glass, at anywhere from 0.26 to 10 percent by weight, with the lower amounts more common. The sources give different typical figures: the Corning Museum of Glass says the color is usually obtained with about 0.5 percent, while ORAU’s Museum of Radiation and Radioactivity puts Vaseline glass at about 2 percent and some glass from the early 1900s as high as 25 percent. Yellow and yellow-green are the commonest colors, NUREG-1717 says, with orange, vermillion red and white also made. Its list of known pieces is drinking glasses, wine glasses, tumblers, candy dishes, vases, pitchers, goblets, ash trays and candlestick holders. ORAU calls a black light in the dark perhaps the most reliable way to find uranium in glass: if the glass glows a rich green, it contains uranium.

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Why it glows under a black light

The glow is fluorescence. Paul Frame, the retired ORAU health physicist who curates its museum, describes it as a visual effect of ultraviolet light interacting with the uranium in the glass. An expert answering for the Health Physics Society adds that the glow is ordinary light, not ionizing radiation, and that it can’t be burned out, even by keeping the glass under lights day and night. The Corning Museum of Glass gives uranium a very strong bright-green response, the strongest of the common ingredients that make glass fluoresce.

The same effect changes how the glass looks in daylight. ORAU says it explains why a piece that looks yellow under incandescent light can take on a greenish tinge outdoors, and NUREG-1717 notes that glass which is yellow-green in transmitted light may look emerald green in reflected light. There are exceptions: ORAU has a yellow glass “gemstone” that contains uranium and does not fluoresce.

Glass that glows but isn’t uranium glass

Not every glow is uranium. Robert Brill, a research scientist at the Corning Museum of Glass, says a weak to moderate yellowish-green fluorescence usually means manganese was added as a decolorizer, a common response in non-lead glass of many periods. Corning describes manganese’s glow as a “lemonade-like” greenish-yellow that is usually not strong, set against uranium’s very strong bright green; lead glass gives an icy blue. It also happens the other way round. ORAU notes that some yellow or yellow-green glass is colored with other additives, such as cerium oxide, can look exactly like uranium glass, and may even be radioactive from thorium impurities.

Uranium glass or Vaseline glass?

The names overlap but are not the same. ORAU uses Vaseline glass for transparent yellow to yellow-green glass colored with uranium, and calls uranium glass the older and more general term, since uranium also colors opaque glass such as custard glass and Burmese glass. Canary glass is older still: ORAU dates it to the 1840s. The Maryland Archaeological Conservation Lab adds jadite, an opaque whitish-green, to the uranium glasses. The EPA’s page on radioactive antiques gives Vaseline glass and canary glass as nicknames for yellow uranium glass.

How it began

The Corning Museum of Glass dates the earliest reference to uranium glass to 1817 and credits Josef Riedel, in Bohemia, with making it popular in and after 1834; his yellow and green were called Annagelb and Annagrün. The Victoria and Albert Museum’s record of a Riedel goblet says he experimented with tinting glass from about 1830 to 1848 and is said to have named the glass after his wife, Anna. It gives a different recipe for the yellow: Annagrün is a uranium glass, it says, while Annagelb’s color came from antimony or silver chloride. Other glasshouses copied Riedel’s technique, the Harrach Glassworks among them. The Maryland lab, which notes small amounts of uranium oxide in the glass of first-century Roman mosaics and Martin Klaproth’s identification of the element in 1789, says uranium glass became popular in Europe after 1820, particularly in Bohemia, and in the US from the 1830s, and Michigan State University’s Campus Archaeology Program puts its height of popularity from the 1880s to the 1920s.

The wartime gap, about 1943 to 1958

US production stopped during the Second World War, and the sources give slightly different years. Michigan State’s archaeologists say production stopped in 1943 under heavy regulation of uranium and resumed in 1958, when uranium was deregulated; a second post of theirs says civilian use of uranium was heavily regulated from 1942 to 1958. The Maryland lab puts the halt just before the war and its end in 1958, when uranium oxide was deregulated. ORAU describes a gap of fifteen years or so beginning in the war, with production resuming in 1959, and says glassmakers used natural uranium before it and depleted uranium after. A 1980 NRC study (Buckley and others, NUREG/CR-1775) estimated that at least 4,160,000 decorative pieces were made in the US between 1958 and 1978, and 15,000 drinking glasses between 1968 and 1972.

Is uranium glass radioactive?

Yes, slightly. NUREG-1717 looked at three ways the glass can expose people: beta particles to the hands while holding it, beta and gamma radiation while near it, and uranium leached into food or drink that has been in contact with it. For glass with 10 percent uranium by weight, it put the gamma dose rate from a decorative piece at 0.0018 mrem an hour at 1 foot (30 cm) and 0.00005 mrem an hour at 6 feet (1.8 m). ORAU sets those beside the background rate from gamma rays, about 0.01 mrem an hour. The beta dose rate in contact with a 10-inch (25 cm) plate was 27 mrad an hour. NUREG-1717 estimated 2 mrem a year for a person with such glassware in the home and 4 mrem a year for the most exposed person, the driver of the delivery truck from the factory; ORAU puts that at about 1 to 2 percent of the average American’s yearly radiation exposure.

In the leaching tests NUREG-1717 cites (Landa and Councell, 1992), drinking glasses left for 24 hours released on average 0.052 micrograms of uranium per liter into water and 5.9 into acetic acid, and less each time the test was repeated. An expert answering for the Health Physics Society says the bigger concern with uranium is its chemical toxicity rather than its radiation: once in the bloodstream, it can damage the kidneys. The EPA says radioactive antiques are usually not a health risk while they are intact and in good condition, and that a chipped piece used for food can put particles of uranium into it.

What US law says

NRC rule 10 CFR 40.13 exempts glassware from licensing if it contains no more than 2 percent source material by weight (in glassware, normally uranium, NUREG-1717 says), or 10 percent for glassware made before 27 August 2013. The exemption doesn’t cover glass brick, pane glass, ceramic tile or other glass used in construction. NUREG-1717 traces an exemption for glass products back to 1947, and the present glassware exemption to a rule of 1961.

Is uranium glass still made?

The sources disagree. The EPA says that after 1970, US glassmakers stopped using radioactive materials for color, though some other countries still use them and such glass still reaches the US. ORAU listed four US companies still making Vaseline glass in 2004 (Boyd Crystal Art Glass, Mosser, Summit Glass and Fenton), all of it decorative and none of it dinnerware. NUREG-1717 (2001) also found US production limited to decorative pieces, from one of the few known domestic makers.