Uranium glass is made by adding uranium oxide to a standard glass melt, typically at concentrations between 0.1% and 25% by weight, depending on the era and desired effect. The uranium acts as a colorant, producing vivid yellow-green hues and the signature bright green fluorescence under ultraviolet light. While the chemistry is straightforward, manufacturing uranium glass today requires a federal license from the Nuclear Regulatory Commission.
The Base Glass Formula
Uranium glass starts with the same ingredients as most everyday glass: silica (sand), soda (sodium oxide), and lime (calcium oxide). This soda-lime silicate base has been the workhorse of glassmaking for centuries. Some historical formulas also included alumina (aluminum oxide) to improve durability and chemical resistance. The uranium component is introduced as uranium oxide powder, which dissolves into the molten glass and bonds within the silica structure.
The oxidation state of the uranium matters enormously. Uranium in its fully oxidized form (hexavalent) dissolves far more readily in glass, up to 13 to 20 mol% at typical melting temperatures. In its reduced form (tetravalent), solubility drops to between 1 and 5 mol%, and in some compositions barely exceeds 1%. This is why the furnace atmosphere and melting conditions directly affect both the color and clarity of the finished glass. Oxidizing conditions favor bright yellow-green tones, while more reducing conditions can shift the color toward deeper greens or even black.
Melting Temperatures and Process
Standard soda-lime glass melts at roughly 1,400 to 1,500°C. Adding uranium oxide doesn’t dramatically change this for typical concentrations of a few percent. However, specialty formulations with very high uranium content (20 to 25% uranium oxide) in alumino-silicate compositions have been melted at 1,700 to 1,800°C. These extreme temperatures were used in research and industrial contexts, not decorative glassware.
In practice, historical glassmakers mixed uranium oxide powder into their batch of sand, soda ash, and limestone before loading it into a crucible furnace. The batch was heated until fully molten and homogeneous, then worked using standard glassblowing or pressing techniques. The uranium dissolves completely into the melt, so the finished glass is uniform in color rather than streaked or speckled.
How Much Uranium Goes In
The amount of uranium varies widely depending on the intended product. Most Vaseline glass, the classic bright yellow-green variety popular from the mid-1800s through the 1940s, contains about 2% uranium by weight. Some pieces from the early 1900s pushed as high as 25%, producing intensely colored and highly fluorescent glass. Modern production, where it exists, tends to stay at the lower end of the range.
Under current U.S. regulations, finished glassware sold to consumers can contain up to 2% source material by weight without requiring the buyer to hold a license. Glassware manufactured before August 2013 was permitted up to 10%. These limits apply to the finished product in consumers’ hands, not to the manufacturing process itself, which has its own licensing requirements.
Types of Uranium Glass
Not all uranium glass looks the same. The concentration of uranium, the oxidation state, and the presence of other colorants produce distinctly different styles:
- Vaseline glass is the most recognizable type, named for its resemblance to petroleum jelly. It’s transparent yellow-green and fluoresces brilliantly under UV light. Uranium is the primary or sole colorant, typically around 2%.
- Custard glass is opaque and creamy yellow, sometimes with a slight green tint. It gets its opacity from the addition of bone ash or other opacifiers alongside the uranium.
- Burmese glass blends uranium with gold compounds to produce a gradient from yellow to pink. The pink develops through a controlled reheating process called “striking.”
- Depression glass refers to mass-produced, often pale green tableware from the 1920s and 1930s. Many pieces contain small amounts of uranium, though not all green Depression glass is uranium glass.
Why You Can’t Legally Make It at Home
The NRC is explicit: the exemptions that allow consumers to buy and own uranium glass “do not authorize the manufacture of any of the products described.” Anyone who wants to manufacture glass containing uranium must hold a specific NRC license (or an equivalent Agreement State license) under 10 CFR 40.52. This applies even if you intend to make a single piece for personal use, because acquiring and processing raw uranium oxide powder is itself a regulated activity.
The safety concerns are real. The U.S. Department of Energy’s safety data sheet for uranium oxide powder calls for local exhaust ventilation at minimum, full disposable coveralls including head and foot coverings, protective gloves, appropriate eye protection (no contact lenses), and at any detectable airborne concentration, a full-facepiece self-contained breathing apparatus operated in positive-pressure mode. Uranium is both a radioactive material and a heavy metal toxin. Inhaling or ingesting the fine powder during batching is the primary danger, far more hazardous than handling the finished glass.
Radiation Levels in Finished Glass
Once the uranium is locked inside the glass matrix, the radiation exposure from handling finished pieces is low. A typical uranium glass bowl measures about 5 microsieverts per hour at close range. For context, natural background radiation averages about 3 millisieverts per year, or roughly 0.34 microsieverts per hour. So holding a uranium glass bowl exposes you to about 15 times background, but only for as long as you’re in contact with it. Setting it on a shelf across the room drops the exposure dramatically.
The more practical question for collectors is whether uranium leaches into food and drinks. A U.S. Geological Survey study tested 33 glass items by soaking them sequentially in water, dilute acetic acid (simulating acidic foods like vinegar or citrus juice), and strong nitric acid. The maximum uranium leached from glass items was about 30 micrograms per liter, a small amount. Ceramic pieces with uranium-containing glazes were far worse, leaching up to 300,000 micrograms per liter. If you own uranium glassware, occasional decorative use is low-risk, but storing acidic beverages in it for extended periods is worth avoiding.
Where Uranium Glass Is Still Produced
A handful of licensed manufacturers still produce uranium glass, primarily for collectors and specialty markets. In the Czech Republic, which has a long tradition of Bohemian glassmaking, some studios continue to work with uranium colorants. In the United States, licensed production exists but is uncommon, partly because of the regulatory overhead and partly because demand is niche. Most uranium glass on the market today is vintage, sourced from antique shops, estate sales, and online auctions where pieces from the 1880s through the 1940s remain widely available.