Geek Trivia

Vintage Marbles Glow Brilliantly Under Blacklight Thanks To What?

Milk Glass
Which Creature Cannot Survive In A Micro Gravity Environment?

Answer: Uranium

Many vintage marbles have a curious property that delights kids and adults alike: if you shine a black light (or other concentrated UV source) on them, they fluoresce an absolutely brilliant green color.

Why do some vintage marbles shine brilliantly and some simply react to the presence of the black light like any other glass? The secret is the composition of the glass: many vintage marbles were manufactured with uranium infused glass. When illuminated by concentrated UV, the glass shines an intense (and stereotypically “radioactive”) green.

But why would anyone add uranium, however trace the amount, to glass marbles? Especially when you consider that back in the 1920s nobody was walking around with a pocket black light to make their marbles glow. Uranium infused glass, commonly called “Vaseline glass” by collectors because of its slightly cloudy appearance, takes on a special appearance when exposed to even the smaller concentration of ultraviolet light rained down upon us by the sun. Uranium infused glass vases, bowls, and prisms, and glass door panels took on a beautiful almost opalescent emerald quality when sunlight hit them just right.

Uranium glass use fell out of favor during the late 1930s and 1940s as the United States government snapped up all available Uranium for nuclear research, development, and weapons construction purposes. Today, a small handful of marble companies still make small runs of marbles with uranium glass and an even smaller number of glass artisans still craft vases, bowls, and decorative objects with the curious glass.