Uranium Glass

By Les Hansen
Issue # 370 - February 2004

Uranium was used by the Cambridge Glass Company to add yellow or green color as well as fluorescence ("glow") to glass it made. Seven Cambridge color formulas contained uranium. Three were opaque colors - Primrose, Jade, and Ivory, and four were transparent colors - Topaz, Light Emerald, Gold Krystol, and Pistachio. Formulas for all of these colors, except Pistachio, were provided in Henry T. Hellmer's Batch Book of Glass Formulae, which was published by J. W. Courter in 2002. The formula for Pistachio was obtained from another batch book of Cambridge colors. The amount of uranium in these Cambridge colors was small - less than 1% - with the exception of Primrose. The amounts per batch (with 1000 pounds of sand as a base), both in pounds and as a percentage of the total weight of the formula were:

Color  by Weight   by Percentage
Primrose 59.25 lb 2.9%
Jade 3.44 lb 0.2%
Ivory 7.00 lb 0.3%
Topaz 12.50 lb 0.7%
Light Emerald 3.20 lb 0.2%
Gold Krystol 1.00 lb 0.1%
Pistachio 1.25 lb 0.1%

It is generally known that uranium is a key ingredient for most "vaseline" (transparent light yellow or green) glass. Technically, Topaz, Light Emerald, Gold Krystol, and Pistachio are all vaseline glass, because each color glows to some extent under black light and is a light transparent yellow or green. Commonly, Cambridge items that are Light Emerald are referred to as vaseline glass when listed for sale to collectors, especially on the internet. However, among these four transparent colors made by Cambridge, only Topaz has the characteristic light yellow-green color and intense glow associated with vaseline glass by collectors. Therefore, Topaz's comparatively large content of uranium was expected.

Uranium's contribution to three of Cambridge's opaque colors might be a bit surprising. The relatively large amount of uranium in Primrose (over 59 pounds is a lot of uranium to add to a batch of glass!) probably would not have been expected by most collectors of Cambridge glass. The question then arises, should collectors be cautious in handling their Primrose-colored Cambridge glass?

An excellent resource on uranium-bearing glass is the website of the World Nuclear Association (www.world-nuclear.org) and, especially, the information provided at a linked website by the Online Glass Museum of New Zealand. The following details were pulled from that reference.

"The most striking thing about uranium glass is that it is radioactive. If you apply a Geiger counter, you will get a positive reaction. However, tests have shown that the radiation levels from even large quantities of uranium glass at close quarters are no more harmful than those associated with television sets or microwave ovens."

"Uranium was a common source of yellow and green coloring for over a hundred years. However, in the 1940s, it was banned as a glass constituent because uranium was used to make the atom bomb and, consequently, there were fears for the health of glassworkers. During the 1950s, these restrictions were lifted, and some companies now use uranium as a colorant occasionally. However, there are other chemicals which can now be used to produce the same colors, and the price of uranium is high. There are also rigorous control regulations covering protective clothing for workers, lead shielding for storage areas, and monitoring of radiation."

Being a solid material, glass is a barrier to meaningful loss of radiation from uranium it might contain. Therefore, an insignificant amount of radiation is emitted from intact glass with normal use. However, grinding and polishing uranium-bearing glass results in dust, which could theoretically be harmful if inhaled or ingested. Because of this potential risk to human health, professional glass grinders are sometimes prohibited from public buildings where glass shows are conducted.

Boyd, Summit, and Fenton all continue to use uranium for glassmaking today.