Clay Times Back Issues Vol. 2 Issue 4 • May/June 1996 - Page 19

Studio Health & Safety Uranium: Still Ticking in Some Potteries BY MONONA ROSSOL Most potters know that uranium can be used as a glaze colorant. And old recipe books say that it’s safe. It’s not surprising, then, that I still get inquiries about uranium. Can we buy it? In the U.S., you are allowed to purchase up to 150 pounds of “depleted” uranium a year without any special license. What is “depleted” uranium? Uranium is an element which has isotopes, that is, varieties that have different molecular weights. Uranium’s three natural isotopes are: U-238, U-235, and U-234. Only U-235 has the right weight for atomic reactions. “Depleted” uranium is uranium from which U-235 has been removed. In the 1970s and 1980s, some fuzzy-thinking potters, teachers and ceramic chemical suppliers incorrectly assumed that “depleted” uranium was not radioactive. This misinformation found its way into many books and publications. While depleted uranium is less radioactive, it is still a significant hazard because all isotopes of uranium are radioactive. Should we use it? In a 1980 review*, the Nuclear Regulatory Commission (NRC) said the use of uranium in glazes should not be allowed. However, the NRC decided not to waste its time banning them because their investigation showed that there were no known commercial producers of uraniumglazed ware in 1980. The NRC also investigated uranium use in art pottery and enamels. They talked to “the art department of a major university,” a “spokesperson for an enamelists guild,” and the “purchasing agent for one of the ten largest public school districts in the U.S.” These people all denied using or buying any uranium. (Surprise, surprise!) Then in 1984, the NRC banned uranium-containing enamels after a lot of radioactive jewelry was imported into the U.S. This also meant that domestic uranium enamels such as Thompson’s Burnt Orange #153 and Forsythia #108 were taken off the market. (I still find stockpiles of these enamels in schools.) As late as 1985, however, potters still found uranium available in a ceramic catalog and Ceramics Monthly published a letter whose author tried to convince potters that depleted uranium was no more radioactive than potassium! I still occasionally find uranium oxide in university ceramics departments and suspect there are closet uranium-glazers out there to this day. Even without a ban, the fact that the NRC is on record saying that uranium glazes should not be allowed puts uranium-users at a moral and ethical disadvantage. And just imagine explaining it to your customers! Radon —Uranium emits both radiation and a cancer-causing radioactive gas called “radon.” Uranium-containing fossils and rocks in museum collections have been shown to require special ventilation to control radon from these specimens. Radon also is emitted from uranium oxide chemicals or even large stocks of uraniumglazed ware. Radon, of course, also could be present in basement pottery studios from radioactive minerals in the soil or in cement. EPA recommends that all homeowners test for radon. Toxicity—Unrelated to its radioactivity, uranium is also toxic to the kidneys and can cause blood disorders. To protect workers from uranium dusts, OSHA assigned a permissible exposure limit of 0.2 milligrams per cubic meter 3 (mg/m ) in air for insoluble com3 pounds and 0.05 mg/m for soluble ones. Craft workers also could inhale uranium dusts during glaze or enamel mixing and application, or by inhaling kiln fumes. Exposure by ingestion could also occur from using leaching uranium-glazed or enameled foodware. How to dispose of it. If you still have a uranium-containing material tucked away, get rid of it. Most communities have a toxic waste program where you can take it on certain days each year. This service is usually free if you are an ordinary householder. However, if the materials are related to your “business,” you are supposed to call a commercia