Glass that fluoresces bright green under ultraviolet light is surely the ultimate yard sale find, but snoopers may have unknowingly passed up on a uranium glass find owing to the fact that it’s not necessarily all that recognizable in the light of day. However, pop that same glass under ultraviolet light and you’ll be rewarded with a dinner display of epic proportions.

Uranium glass is – unsurprisingly – glass that’s been cut with uranium and depending on the quantity it can vary from opaque to see-through. It can be green or clear in color, but in a dark room with a UV light, it fluoresces bright green.

What is uranium glass?

Swirling uranium into glassware first began back in the 1830s, says the Museum of Radiation and Radioactivity, as a means of adding color to glass. In the same way that other heavy metals have been used to color glass throughout its creation, uranium was thrown in for its green hue long before we understood its energy potential.

It’s estimated that more than four million decorative pieces were churned out in the US between 1958 and 1978. That’s a lot of glowing glassware.

Most of the novelty glass contained less than 2 percent uranium, but a few choice pieces from the early 1900s can be one-quarter uranium. Uranium is a heavy metal and naturally radioactive element that’s earned it a spot in the recipe pages for an atomic bomb, which begs the question…

Is uranium glass safe?

When it comes to radiation exposure risk, some of the “hotter” uranium glass products have a higher capacity than others to increase a person’s annual exposure. These include earlier pieces with a higher concentration of uranium which are more likely to leach into food or drink contained in the glassware and expose hands to higher doses of radiation, though this is still quite low.

Some uranium glass was created with natural uranium but after World War II, using depleted uranium (DU) became more common. DU comes with the benefit of mostly releasing alpha radiation which can’t penetrate the skin so isn’t considered a serious hazard outside of the body.

The “Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials” set out to investigate the various exposure routes (leaching and skin contact) and potential doses of radiation from uranium glass. They found that the people most at risk from the products were actually the people responsible for shipping them.

As for the recreational uranium glass owner, they estimated that the maximum estimated dose only represented around one to two percent of an American’s average annual radiation exposure. However, the International Gem Society warn against cutting uranium glass without following safety precautions.

How to identify uranium glass

Some examples of uranium glass, such as vaseline glass, can be easy to spot with the naked eye if you know what you’re looking for, which is glass the color of a wad of petroleum jelly. For clearer glass, however, you may need an ultraviolet light and a dark room to reveal its radioactive potential.

A positive sign for uranium glass is a rich green glow under the ultraviolet light, and keen collectors use black lights and Geiger counters to hunt down the real deal. There are some exceptions that won’t glow even though they contain uranium, but where’s the fun in that?

If you’ll excuse us, we’re off to hit up some thrift stores.