The works pictured above, all made by Karl Martz in the 1930's and early 1940's, employ uranium glazes. They emit radioactivity easily detectable with a Geiger counter.

Since earlier than 79 A.D., uranium oxides and salts were used in glasses and ceramic glazes to achieve rich yellows, oranges, and reds (under oxidizing conditions). After uranium began to be used for nuclear weapons and power plants, the material available for pottery was "depleted uranium", depleted of the isotope of uranium (²³⁵U) utilized for nuclear fission. Depleted uranium is somewhat less radioactive. Uranium is very toxic, both chemically and as a radioisotope. Its use in ceramics was restricted by the US Government beginning in 1943, but resumed (with depleted uranium) in 1959 through the 1970's. See also

• Health Physics Society: Uranium in dinnerware and art glazes and Radiation doses from uranium dinnerware.
• Uranium and Ceramics.
• Uranium (history, chemistry, physics).
• Uranium (Environmental Protection Agency).
• Fiesta Ware at Auction