Uranium tile
Uranium tiles have been used in the ceramics industry for many centuries, as uranium oxide makes an excellent ceramic glaze, and is reasonably abundant. In addition to its medical usage, radium was used in the 1920s and 1930s for making watch, clock and aircraft dials. Because it takes approximately three metric tons of uranium to extract 1 gram of radium, prodigious quantities of uranium were mined to sustain this new industry. The uranium ore itself was considered a waste product and taking advantage of this newly abundant resource, the tile and pottery industry had a relatively inexpensive and abundant source of glazing material. Vibrant colors of orange, yellow, red, green, blue, black, mauve, etc. were produced, and some 25% of all houses and apartments constructed during that period (circa 1920–1940) used bathroom or kitchen tiles that had been glazed with uranium. These can now be detected by a Geiger counter that detects the beta radiation emitted by uranium's decay chain. In most situations, the radiation exposure is not excessive, but there may be exceptions for pure uranium oxide (which produces red-orange coloration as a glaze) on bathroom floors, which can pose a hazard for infants crawling around.
The use of uranium in ceramic glazes ceased during World War II when all uranium was diverted to the Manhattan project and didn't resume until 1959. In 1987, NCRP Report 95 indicated that no manufacturers were using uranium-glaze in dinnerware.[1]
Potential doses
Although the uranium in the glaze emits gamma rays, alpha particles, and beta particles, the gamma and alpha emissions are weak. The beta particles are the easiest to detect, and they are also responsible for the bulk of the radiation exposure to those handling ceramics that employ a uranium glaze.
NCRP Report 95 reported the following measurements for dinnerware employing uranium glazes: 0.2 to 20 mrad per hour on contact as measured using film badges;
NUREG/CRCP-0001 reported a measurement of approximately 0.7 mR/hr at 25 cm from a Fiesta red dinner plate. It also reported the results of an Oak Ridge National Laboratory analysis that predicted 34.4 mrem/year to a dishwasher at a restaurant using ceramic plates containing 20% uranium in the glaze, 7.9 mrem/year to the waiters, and 0.2 mrem to a patron for a four-hour exposure.
It is likely that the major health issue associated with this dinnerware is not the radiation exposures but the ingestion of uranium or other heavy metals that have leached into food or drink in contact with the dinnerware. One FDA study measured 1.66 x 10−5 uCi/ml in a 4% acetic acid solution in contact with the ceramic dinnerware for 50 hours. This exceeded the ICRP's maximum permissible concentration (MPC).
One common misconception is that a uranium-containing glaze can be a source of 222Rn. This is incorrect because the glaze contains chemically purified uranium, not the complete uranium series. Chemically purified uranium contains: 238U plus its two short-lived decay products, 234Th and 234mPa; 234U; and 235U plus its decay product 231Th. Since 226Ra is not present, there is no radon (222Rn) production. It is true that the clay used to produce the body of the ceramic (rather than the glaze) can be a source of radon, but this is true for all ceramics, with or without a uranium glaze.
Ordinary ceramics often contain elevated levels of naturally occurring radionuclides, e.g., 40K and the various members of the uranium and thorium decay series. Because of this, health physicists who are conducting radiation surveys expect to see higher readings when they are making measurements over ceramic tiles and similar materials. Sometimes the higher readings are due to uranium in the glaze; sometimes they are due to the radionuclides in the clay that was used to produce the ceramic.
Reported examples include a vehicle carrying toilets setting off a radiation monitor at a truck weigh station, and health physicists at Oak Ridge National Laboratory reporting excessively high readings while surveying newly purchased urinals for the men's restrooms.
Ceramics can be particularly radioactive if some compound of uranium (e.g., uranium oxide, sodium urinate) has been used to impart color (e.g., orange-red, green, yellow, black) to the glaze.
Background
Not long after Henri Becquerel discovered radioactivity in uranium salts, Madame Curie discovered both polonium and radium as two new radioactive elements also present with uranium. The relatively high specific activity and moderate half-life of 1,600 years of 226Ra, the main radioisotope of radium found in uranium ore, made for a material which when mixed with a phosphor allowed for a glow-in-the-dark substance.
Thus, in addition to its medical usage, radium usage also became a major industry in the 1920s and 1930s for making watch, clock and aircraft dials. The radium dial painters brought a certain degree of notoriety to the abuse of radioactive materials, and that precautions needed to be followed with this new substance.
Because it takes approximately three metric tons of uranium to extract 1 gram of 226Ra, prodigious quantities of uranium were mined to sustain this new industry. The uranium ore itself was a "waste product" of this industry. By some estimates, nearly one million tons of uranium were mined to support this industry.
Taking advantage of this newly abundant resource, the tile and pottery glazing industry then had a relatively inexpensive and abundant source of glazing material that produced a wide variety of colors depending upon admixtures, firing, etc.
Vibrant colors of orange, yellow, red, green, blue, black, mauve, etc. were produced on tiles and other ceramic materials, and by some estimates, some 25% of all houses and apartments constructed during that period (circa 1920–1940) used varying amounts of bathroom or kitchen tiles that had been glazed with varying amounts of uranium. These can now be readily found in older homes, apartments, and other buildings still standing from that era by use of a simple Geiger counter that readily detects the beta radiation emitted by uranium's ever-present decay chain radio-daughters.[2]
After EURATOM restrictions about uranium uses in ceramic glazes, there are no factories left working with uranium glazes, which is why uranium glazed tiles have become rare pieces for collectors.[3]
These glazes are generally made with 238U raw material, known as yellowcake UO2 uranium granules. 21st century contemporary ceramic artist and academic researcher Sencer Sari is one of the known specialists who is working with these uranium glazes.[4]
In most situations, the radiation exposure is not excessive, but there are some exceptions in which pure uranium oxide [which produces red-orange coloration as a glaze] on bathroom floors can pose a hazard for infants crawling around for hours on end, day after day.
References
- Harry McMaster. Earthenware Dishes and Glaze Therefor. Patent No. 1,890,297,
- http://www.nbcnews.com/id/3077213/ns/technology_and_science-science/t/uranium-hunter-follows-trail-tiles/ Uranium hunter follows trail of tiles
- msnbc.com, Alan Boyle (2003-12-12). "Uranium hunter follows trail of tiles". msnbc.com. Retrieved 2019-05-28.
- http://sencersari.com/wrd/?page_id=2101