This week’s blog focus is uranium glass (also called Vaseline or canary glass). Although seemingly non-descript under incandescent lighting, these objects fluoresce brilliantly when viewed under an ultraviolet black light. The glow produced by these objects is a result of the colorant used in the vessels – uranium. Uranium glass was widely popular and was produced by several Pennsylvania glass manufacturers. While using uranium glass for food consumption is not recommended, they usually pose little danger to people.
Photo by Melanie Mayhew (private collection)
The hidden properties of uranium glass are revealed under a black light.
Uranium was formally discovered over 220 years ago by German chemist Martin Klaproth. Klaproth named this element “uran” after the planet Uranus. As with the discovery of other brightly colored compounds and elements, uranium soon became a popular pigment. The first documented use as a glass colorant was recorded in 1817 (Lole 1995). Its popularity as a colorant in Europe later spread to the United States and Japan. Natural uranium was used to color glass, enamels, and ceramic glazes until the 1940s when the onset of World War II resulted in a production gap of uranium-containing housewares. Depleted uranium was made available for use beginning in 1959. Although uranium use as a colorant has decreased dramatically in recent decades, some contemporary objects claiming to contain uranium can still be found for sale online.
Photo by Andrew Silver, USGS, Public domain, via Wikimedia Commons
The natural yellow to green color of uranium ore led to the widespread use of this material as a colorant.
Uranium glass is most frequently associated with yellow to yellow-green colors, but fluorescent objects were later made in a range of colors. There is a lack of awareness around the widespread use of uranium colorants (Strahan 2001), possibly because without a black light or specialized knowledge of uranium colorants, identification by archaeologists can be easily missed. Archaeologists use several observational methods to identify and classify artifacts, and a UV light is a useful tool to assist with the identification of objects containing radioactive colorants. The Corning Museum of Glass identifies several other components used in glass manufacture that may also fluoresce, such as antimony (light pink or pink-orange), manganese (yellow), and glass with a high lead content (bluish white).
Photos by Wombat1138, Public Domain via Wikimedia Commons
Glass objects containing radioactive material have been made in a range of colors, making their identification more difficult.
Pennsylvania's rich resources, including sand, coal, and flint, contributed to its importance as a glass manufacturer. By the time of the Civil War, Pittsburgh, Pennsylvania was the premier city for glassworks in the United States. Many glass manufacturers in Pittsburgh produced a range of uranium glass housewares to satisfy consumer demand at the turn of the 20th century.
For those with a fondness for these objects, the Environmental Protection Agency (EPA) indicates there is usually little health risk involved with keeping antiques containing radioactive materials, if they are in good condition. Moreover, an additional source indicates little health risk unless objects are stored in a small area, are used to store and consume large quantities of acidic or alkaline foods, or if the object must be drilled for conservation work thus creating a dust from the removed material (Strahan 2001).
We hope you have enjoyed this blog on the hidden properties of uranium glass. We invite you to explore related objects by searching for the popular term “Vaseline glass” in the Pennsylvania Historical and Museum Commission’s online collections database.
Argonne National Laboratory
N.D. Uranium Quick Facts. Depleted UF6 Guide. https://web.evs.anl.gov/uranium/guide/facts/, accessed August 10, 2021.
Corning Museum of Glass
N.D. Conservation Laboratory. Conservation. https://www.cmog.org/collection/conservation/laboratory, accessed August 10, 2021.
Environmental Protection Agency (EPA)
N.D. Radioactivity in Antiques. Radtown. https://www.epa.gov/radtown/radioactivity-antiques, accessed August 10, 2021
Heinz History Center
N.D. Glass: Shattering Notions. Exhibits. https://www.heinzhistorycenter.org/exhibits/glass-shattering-notions, accessed August 10, 2021
Lole, F. Peter
1995 Uranium Glass in 1817- A Pre-Riedel Record. Journal of Glass Studies 37:139-140.
2001 Uranium in Glass, Glazes and Enamels: History, Identification and Handling. Studies in Conservation 46(3):181-195