Some glassware collectors take a handheld black light along with them when they shop in order to test Vaseline glass, also known as canary glass or uranium glass. Real uranium glass will glow green under a black light. Glassmakers began using uranium as a coloring agent in the late 1700s, but it wasn’t until the 20th century that we knew how dangerous radioactivity is. Still, Vaseline glass continued to be made, with the exception of the World War II years, up to the present day. That’s because the tiny amounts of radiation emitting from Vaseline glass are smaller than radiation emitted from many other things we encounter in our everyday lives. So why does it glow?
Even if radioactivity is the thing that makes Vaseline glass cool, it’s not what makes Vaseline glass glow, says Barrie Skelcher, who’s written two Vaseline glass books of his own. That may come as a surprise to many Vaseline glass collectors, who assume that radioactivity is the reason why Vaseline glass glows under ultraviolet light, confusing the cartoon depiction of radioactivity for the science.
“It’s the chemistry of uranium that makes Vaseline glass glow, not radioactivity,” Skelcher says by phone from England, where he lives with his wife, Shirley, and 500 or so pieces of Vaseline glass in a collection that once numbered more than 1,000. “It wouldn’t make any difference whether the glass contained depleted uranium with the 235 isotope removed or natural uranium; the chemistry is identical. Uranium fluoresces under UV light.”
In other words, glass containing uranium will glow under UV light even after all the radiation has, er, radiated. The danger associated with uranium glass pales in comparison with glass that contain lead, arsenic, cobalt, or a number of other colorants and additives. And you’ll receive more dangerous radiation from the black light than from the glass. Still, the story of Vaseline glass is fascinating. I was surprised to learn that the name “Vaseline” was given to uranium glass because that’s the color Vaseline used to be! (Eww.) You can read plenty more about Vaseline glass at Collectors Weekly.
(Image credit: Dave Peterson at Vaseline Glass Collectors, Inc.)