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Uranium in Ceramic Glazes

This information has been cut-and-pasted from a discussion on ClayArt during late 2003 and early 2004. The dialog was started because someone submitted an old glaze containing uranium. You decide what you think after listening to people who clearly know something about the topic. We have lost attribution of some of this material, if you are the author and wish to clarify, edit or remove it please contact us.

Uranium is a naturally occurring element in soils and rock. There are many different isotopes of uranium, each with a different combination of alpha, beta, gamma, and xray emissions. Uranium is primarily an alpha emitter (97-98%), but it is also a low level x-ray emitter (2-3%). Although there is background radiation all around us, use of low radiation materials adds unnecessarily to this.

Dangers from handling uranium glazes or uranium-glazed pieces.

Legally, in the United States, you may not sell a piece that contains uranium to an individual. You may sell it to another business (if you let them know they are buying pottery, glass, whatever, that contains uranium). Of course, that business is not allowed to legally sell the piece to an individual after purchasing it from you.

Alpha emitters have large particles that can be stopped by the skin, however inside the body, they are more dangerous. Gamma radiation penetrates better but gamma emitters generally have a short half life so ingested gamma emitters don't stay in the body nearly as long.

Unknown Author:

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 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.

THE NUCLEAR REGULATORY COMMISSION (NRC)

In a 1980, the NRC clearly said that the use of uranium glazes should not be allowed ("Environmental Assessment of Consumer Products Containing Radioactive Material," Nuclear Regulatory Commission (NUREG/CR-1775), October 1980). However, NRC decided not to waste its time banning uranium glazes because their investigation showed that there were no known commercial producers of uranium-glazed 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.

As late as 1985, pottery catalogs still listed uranium. To this day, I still occasionally find uranium oxide in university ceramics departments.

In 1984, NRC banned uranium-containing enamels after a lot of radioactive jewelry was imported into the US. 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.

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!

From: Unknown??

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 uranium-glazed 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 home owners test for radon. Combining basement pottery with a radon problem with use of uranium glazes could really boost your total exposure.

TOXICITY

Unrelated to its radioactivity, uranium is also toxic to the kidneys and can cause blood disorders. Soluble uranium from ceramic ware, ingestion of small amounts of glaze or enamel dust from lung clearing mechanisms, or absorption of soluble compounds by the lungs would be potential sources for this kind of toxicity.

To protect workers from the toxicity of uranium dusts, OSHA assigned a permissible exposure limit of 0.2 milligrams per cubic meter (mg/m3) in air for insoluble compounds and 0.05 mg/m3 for soluble ones.

Inhalation of very small insoluble dust particles into the alveoli where there are no lung clearing mechanisms effectively places an emitting radioactive particle in intimate contact with lung tissues.

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. In some cases, these programs have refused to take uranium oxide.

However, if the materials you wish to discard are related to your "business," you are supposed call a commercial company and pay for disposal.

From: Evan Dresel

Marshall is probably referring to the famous orange Fiesta Ware that obtained it's colour from a uranium bearing glaze. This stuff will cause a geiger counter to read off-scale (I don't want to imply any particular level of health hazard or lack there of). So given my other posts about uranium being an alpha emitter which is not measured by geiger counters, what gives?

When uranium decays it produces radioactive daughter products. Most of these are gamma and beta emitters which are detectable if there is enough present. Go back to the formation of the earth. A certain amount of uranium-238 and uranium-235 was present in the cosmic goo which became the earth (appologies to the astro-physicists out there). Most of that has decayed away and the amount we have now is just the remains. Now when the uranium decays it produces a whole chain of radioactive daughter products. Some of those have very short half-lives and you essentially don't see them. Some have longer half-lives and build up to significant levels. I could spend some time explaining this but this whole paragraph is a bit of overkill. The point is that over geologic time uranium deposits end up full of uranium and daughter radionuclides. It takes a very long time but after a while the rock ends up quite radioactive due to these daughter isotopes.

Still with me? Here's where the speculation comes in. I don't think that purified uranium oxide could have been used in Fiesta ware. If that was the case the daughter radionuclides would have been removed and the glaze would not be a beta/gamma emitter. Remember this stuff was made before the 1940s and uranium chemistry was not aswell known as now.

Some of the materials we use in glazes are nearly pure chemicals processed from ores -- cobalt oxide, copper oxide, etc. But some are simply mined, ground up and separated out as minerals. If you take the uranium minerals directly from a mine, you will have uranium and all the daughter isotopes that have built up since the mineral was formed. I think there is very good reason to believe that the uranium used in Fiesta Ware was not separated from the daughters. I mean why bother if you can get by with less costly and less processed material? Just mine and separate out the mineral and use that.

What this means is that you can't compare the risks of using a glaze formulated with uranium oxide with a glaze formulated with a mineral which contained both uranium and uranium daughters. That would be like comparing the risk of smoking cigarettes with the risk of wearing a nicotine patch. (Not the best analogy but you get the idea.)

BTW the advice that the WA Department of Health gives to anyone who owns some of that Fiesta Ware is that it is fine to keep on display in your house but recommends against using it for food.

From: Evan Dresel

There seems to be a lack of understanding of basic radiation physics here. Uranium is an alpha emitter. I don't know how the lab measured the radiation from the beads either -- around here they often use a device called a PAM (Portable Alpha Monitor I think) which is actually quite difficult to use unless you are dealing with something screaming hot because ... Alpha particles have very poor penetration properties. You can stop them with a piece of paper. You can stop almost all of them with the dead layer of your epidermis. You can stop them with your clothes. You can stop them with latex gloves. You don't want an internal dose of alpha particles particularly in the sensitive tissues of your lungs.

Then if you are dealing with pure uranium you are dealing with three isotopes (four if you are thinking of the mostly spent fuel from a nuclear reactor which I think we don't need to worry about here). All three isotopes have very long half-lives. Very long half-life means very few atoms decay in any period of time. That means there is not much radiation to detect. If you want to detect it the easiest way is to dissolve up the material and put it in a liquid scintillation cocktail. That's a special liquid which emits light when it absorbs those alpha particles. Then you measure the light given off with very sensitive photomultipliers. The trouble with trying to measure the radioactivity of the solid is that nearly all of the radiation is absorbed before it even reaches the surface. Even more so when measuring the alpha radiation from a small amount of uranium in a glaze -- It's going to be really difficult to detect.

Ok for those of you who have read all this, what's my point? My point is that I am not surprised at all that the beads didn't read above background. We could get into a really esoteric discussion of what "background" is, but I don't think it is worth it. At the risk of annoying Monona (it has been known to happen :-() if you consider a single alpha particle more than would be present if the material wasn't there then she is right: it will be above background (impossible to measure because the background radiation is fluctuating constantly with time). But that's not exactly a reasonable test and is not generally accepted in the scientific community.

From: Gavin Stairs

Defining the emissions of ionizing radiation from a sample can be tricky. In the case of a small object like a bead, if you simply put it close to a counter and count, you may well decide that it emits no significant amount above background, if the area of the counter is large, or a number of other conditions. This does not mean that the bead is safe to place next to skin. It simply means that if you live next to the bead (in the same room, for example) you won't be absorbing any significant dose of radiation. This is the same effect as being in a room with an incandescent bulb vs. touching the bulb with your skin. The first is not unpleasant, but the second is distinctly unsettling. If you wish to try the experiment, you will find that there is a distance beyond which you cannot feel the heat from the bulb, but as you move closer you feel it more and more until at a certain point you begin to feel pain. Exposure to a radioactive source is like that, only the damage to tissue becomes significant long before you can feel it because we have no direct sensors to ionizing radiation.

The most damaging radiation for mucosa (lungs, mouth, digestive tract) are alphas and disintegration products. Alphas may not even penetrate skin, and they may not penetrate the glaze coat, especially if there is a clear coat over the colour.

The most damaging radiation for close contact to skin, especially if the source is buried in a glaze, is beta (electron) or gamma (photon) radiation. This has the power to penetrate several millimetres of skin. It will also penetrate a clear glaze coat over the colour.

Uranium emits alphas, betas, gammas, neutrons and fission products. If you want to know if a bead is safe to place next to skin, you must read the total activity of the bead and consider that as a skin contact source. There are standard methods of doing this. The U of Alta test was probably a simple matter of placing the bead in front of a survey counter for a few seconds, and judging if the count rate increased significantly, perhaps more than half again as much as background. This is not a sufficient test to determine safety in skin contact. I won't go into the correct methods for testing such a source, since they are somewhat involved, and are the province of experts. They require sensitive and well shielded counters sensitive to the appropriate particles, etc.

I would like to emphasize that unless you know what you are doing and take sufficient precautions, any uranium salt or product is a potential if not an actual hazard to health, even though no prompt symptoms may be detected. People who do handle uranium do so under strict protocols regarding shielding and protective procedures, and with constant supervision of the level of inhaled particles and body exposure. Under such conditions, it is possible to handle the metal and even the salt powders safely. In past, these substances were not handled properly, and many health and safety problems have resulted. Those who are unclear about the large scale problems that can result should look into the situation at Rocky Flats.

Another caution: Radioactivity was not discovered until the turn of the last century. Up until about WW2, the dangers were not appreciated, and safety protocols were rarely instituted. It is dangerous to use prewar practice as examples of proper usage, since our understanding has increase considerably since then. Indeed, most of today's regulations come from the experience of the Japanese population exposed during the bombing of Hiroshima and Nagasaki. The legacy of this is that our data is for high exposures, while what we are discussing is low exposures. There is a current debate about whether the extrapolated high exposure data is suitable for the low exposure. This will not be resolved for some time. It is prudent to continue to regard low level exposures as somewhat hazardous. Certainly, dust particle exposures in lung tissue are hazardous.

From: Evan Dresel

Sigh, uranium again. All isotopes of uranium are radioactive. The three isotopes which make up the bulk of natural uranium are uranium-234, uranium-235 and uranium-238. Nearly all the uranium **by mass** is uranium-238. However, approximately half of the radioactivity is from uranium-238 and half from uranium-234. That's because uranium-238 decays to uranium-234 and uranium-234 has a shorter half life. After a certain amount of time the decay chain reaches steady state and the uranium-234 is decaying at the same rate it is being produced. Uranium-235 produces very little of the radioactivity because there is little of it present (it is however very important to those in the massive eistruction business). In depleted uranium some of the uranium-235 has been removed. Almost certainly an even greater proportion of the uranium-234 has also been removed. How much, I don't know. All of the uranium isotopes are alpha emitters. That means the radioactivity can be stopped by a piece of paper or the dead-layer of your skin. Alpha particles however, can be quite destructive once in your body -- particularly if inhaled into your lungs. Here's the catch -- all the isotopes of uranium have extremely long half-lives. What that means is that there isn't much radiation unless you have a whole lot of the stuff. The proposed drinking water standard for uranium in the US is set mainly by it's possible chemical effect on the kidneys, not on its radioactivity. My suspicion is that uranium is fairly benign in glazes but haven't done enough research. I strongly disagree with the answer, "It's radioactive, it will kill you and your customers."

If you don't want to use radioactive materials in your pottery, you better stop using potash-feldspar and probably nearly every clay. Potassium-40 is present in all potassium containing materials and is quite radioactive. You can measure the radioactivity from the potassium in fertilizer using a simple hand-held geiger counter.

By Tony Hansen
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