Walking around your house with a black light can be hugely illuminating.

For instance:

• I discovered that my handmade ceramic steamer for food contains a disconcerting number of fluorescent green spots (radioactive?)
• I sadly beheld the full extent of pet accidents on our wool rug
• I found that I own four pieces of vintage uranium glass (unequivocally radioactive)

Uranium in Glass

It turns out that uranium gives glass a lovely yellow, yellow-green, or green color. The precise hue depends on the oxidation level.

But under ultraviolet or black light (a type of ultraviolet light), such glass fluoresces vivid—saturated—green, with the brightness reflecting the amount of uranium present. 

Uranium glass is nothing new. The ancient Romans used uranium in glass mosaic tiles as far back as 79 CE. According to V. M. Expósito-Suárez et al. (2022), who evaluated non-destructive means to test collector and museum pieces for radioactivity,

sodium or potassium uranate . . . was used in ancient times due to its colouring properties in pieces manufactured with vitreous materials.

It wasn’t until 1789, however, that uranium was formally identified—by German chemist Martin Klaproth, who named it after the planet Uranus. Soon after, uranium seems to have been used to color glass, although written proof is elusive (Lopes et al. 2008). But by the 1830s, the naturally occurring heavy metal was used as a glass colorant for a wide range of products.

Europeans and Americans alike were enamored with the glass, but few were likely to see it fluoresce. Although Johann Ritter, a German physicist, discovered ultraviolet light in 1801 (violet is the end of the spectrum that we can see; ultraviolet is beyond that), black lights weren’t readily available to consumers until the 1960s.

The advent of WWII brought an end to uranium’s commercial use. When production of uranium glass resumed in 1959, depleted—rather than natural—uranium was used (ORAU). Some uranium glass is still made today, but solely for decorative items.

What’s in a Name?

Various names describe this radioactive glass. In the 1840s, it was called canary glass, which I find rather charming as well as descriptive. 

In the 1950s, it was called Vaseline glass. David Mountfield, who compiled The Antique Collectors’ Illustrated Dictionary, defines the term with candor:

A name given (in some desperation one would think) to a type of coloured glass in the late 19th century, a paleish green resembling the well-known pharmaceutical product.

A colorant, often iron oxide, might be added to Vaseline glass to deepen its green color, but it was always transparent. Uranium content was generally around 2% by weight but could reach 25% (URAU).

The term “uranium glass” predates “Vaseline glass,” but it’s also a more general term and includes semitransparent and opaque pieces. According to Studio Antiques, Vaseline glass contains uranium whereas uranium glass was made with uranium oxide.

There is overlap of uranium glass and depression glass, which was produced from the mid-1920s to the end of WWII. Inexpensive depression glass was usually colored and transparent, although it could be colorless or opaque. And, it could contain uranium.

Well, there’s disagreement about this. To some, Vaseline glass contains uranium whereas depression glass does not. To others, any glassware produced during the depression glass period counts as depression glass, with or without uranium.

Inherited from my grandmother, my pieces were probably acquired during the depression glass years; their decorative motifs seem to square with that. As to the intended use of these glasses, I really don’t know. They don’t seem to be drinking glasses.

The platter (broken when it was shipped to me, unfortunately) seems likely to have been produced during the Atomic Age (1940s–1960s), when atomic patterns were popular.

Uranium Glassware

You can find lots of vintage uranium glassware! Just try googling it and you’ll turn up plenty to buy. The variety of pieces—dishes, platters, glasses, teacups, bowls, pitchers, cream and sugar sets, stemware, decorative items—and decoration motifs are staggering. Shopgoodwill currently has multiple sets of uranium teacups and saucers on auction:

Although the inclusion of a radioisotope in your teacup may seem concerning, the level is said to be safe. The ORAU Museum of Radiation and Radioactivity notes that in tests of food that was put into uranium-containing glass, the person who transported the glass from the producer to the truck distribution center was more at risk than the person who (theoretically) consumed food or beverage served in the glassware.

Still, there’s no chance that I’m serving anyone anything in uranium glass! If you have a pretty uranium glass teacup at home, perhaps it’s best used as a conversation starter rather than for drinking tea.

Sources:
–Lopes, F. et al., “Uranium glass in museum collections,” Journal of Cultural Heritage 9:e64–e68, 2008.
–Mountfield, David, comp., The Antique Collectors’ Illustrated Dictionary, Hamlyn Publishing, NY, 1974.
–ORAU Museum of Radiation and Radioactivity, “Vaseline and uranium glass (ca. 1930s),” accessed 10/3/23.
–Studio Antiques, “What the difference?: Uranium glass, vaseline & depression glasses,” accessed 10/3/23.
–V. M. Expósito-Suárez et al., “Radiological characterization of a uranium glass collectible by gamma spectrometry,” Radiation Physics and Chemistry 199 (110299), October 2022.