Answer to Question #1583 Submitted to "Ask the Experts"

Q

I just recently asked a question and have one additional question to go along with my previous question. We also get calls from the public asking about ceramics. Are there still measurable sources of radioactivity present in the glaze of some ceramics today? (Or am I just confusing this with the old J.B. Hawthorne red plates/etc. that were made prior to 1972?)

A

The use of uranium as a colorant in dinnerware and art glazes increased rapidly during the mid to late 1930s but stopped in the early 1940s due to wartime restrictions. The color most associated with these glazes was a bright orange-red but uranium was sometimes an ingredient in other colors including ivory, yellow, burgundy, green, brown, and black. Commercial production of dinnerware with uranium glazes resumed in the 1950s, reaching approximately 200,000 pieces per year between 1959 and 1969. Probably the best known U.S. producers were Homer Laughlin China Co., with their Fiesta line of dinnerware, and the Bauer Pottery Co. of San Francisco. Domestic production of uranium dinnerware ceased entirely by about 1980 due to environmental, regulatory, and production concerns but radioactive pieces are still relatively easy to find in flea markets, antique shops, Internet auctions, and on collector's shelves. Early uranium glazes also contained large amounts of lead which, like uranium, could leach out in acid foods and may have presented an equal, if not greater, health hazard. Although current regulations permit glazes containing up to 20% by weight of uranium, glazes used on ceramic food containers are now subject to the U.S. Food and Drug Administration approval and no dinnerware containing uranium has been approved since the regulation took effect. Uranium glazes have also been used on technical porcelain. Coors Ceramic, for example, produced a line of black crucibles that were able to withstand very high temperatures and yet remain jet-black. A similar glaze was available on Coors' laboratory spot-plates up until 1989. Thorium is another radioactive material that has been used in glazes, though I have not personally come across any pieces. Moreover, glazes aren't the only possible source of radiation in ceramics. Some ceramics contain measurable amounts of naturally occurring radioactive material (NORM) in the clay itself. To summarize: Easily measurable amounts of intentionally added uranium can be found in many older glazes but this intentional use of radioactive colorants in commercial glazes essentially ceased in the 1970s. The radiation levels associated with modern ceramics can be above background, but would not be described as "easily measurable." Finally, it is also possible that foreign ceramics containing uranium might occasionally enter the country, as was the case with some of the imported cloisonné jewelry during the 1980s. William Kolb For more information on uranium glazes, formulas, activity, and producers see Frame P, Kolb W. Living with Radiation-the First Hundred Years. Another good source of information is "Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials" NUREG-1717.