Clay Culture: radioCHROME Mike Stumbras

Appears in the December 2015 issue of Ceramics Monthly.

The impetus for this project came from a piece of amethystine quartz that I found while walking along Rye beach in New York. As I held the oddly shaped rock up to the sun, I was struck with wonder as light rays bounced around inside the crystal, revealing a subtle, variegated purple hue. I wanted to create a glaze that could capture this quality.

The creation of ceramic glazes designed to mimic precious stones is not a new phenomenon. Historic celadons were admired because of their striking resemblance to jade, while chun glazes are often referred to by the qualities they share with opal. However, some quick research revealed that amethyst and many other gemstones are colored when they are exposed to natural sources of radiation within the earth’s crust.

It wasn’t until two years later that I found myself outside the Louisiana State University (LSU) Nuclear Science Building, which is festooned with radiation warning signs and under constant surveillance. With a twinge of anxiety about the invisible rays of death that could eat my DNA, I was introduced to the gregarious Dr. Wei-Hsung Wang, director of LSU’s Radiation Safety Office and professor at the Center for Energy Studies. He enthusiastically showed me a collection of radiation-related oddities including a few dish-water brown shot glasses that had been irradiated with gamma rays. Dr. Wang, who spoke passionately about radiation technology, encouraged me to try this technique with glazed ceramics.

Ultimately, I teamed up with two radiation specialists at the LSU Radiation Safety Office. Charles A. Wilson IV, a Ph.D. candidate in Environmental Science with a concentration in Health Physics and Amin M. Hamideh, a health physicist. We developed a food-safe glaze that could be predictably colored by exposure to gamma radiation.

I used the glaze calculation program INSIGHT (http://digitalfire.com/ insight/index.php) to do a comparative chemical analysis of known glasses and gems that showed radiation-induced coloration with known ceramic glazes. Along with trial and error, we formulated a few glazes based on chemical analysis, and then subjected the glazes to radiation to mimic the natural process that gems like amethyst go through. We found that numerous classes of glazes exhibit a color change in some form or another when exposed to ionizing radiation.

The Process

Wilson explains the process: “The ceramic mugs are placed in a secure and shielded vault and exposed to a photon source. Energy from the source passes through or is deposited into the glaze. This can excite some elements, shifting around electrons. This change in electrons makes the glaze absorb new colors, which gives it a different appearance.” The optical quality of this glaze changes slightly depending on the quality of light hitting it, which gives a subtle, shimmery effect; most likely produced by the unique configuration of electrons in the color centers of the glaze. Note that unlike Vaseline glass and some glaze colors of the well-known Fiestaware that were produced pre-1972 that utilized radioactive materials in their composition, these irradiated objects do not pose any radiation hazards themselves—This was verified by testing in a high-purity germanium radiation-detection system.

Annealing the irradiated objects between 550–700°F (288–371°C) could further augment the colors by softening them at the cool end of this range or by bleaching it completely above 650°F. Glazes may occasionally reveal another unexpected color with heating in this range.

There are likely many additional color possibilities that this project did not explore. The resulting color appears to be dependent on the amount of radiation received, the structure of the glaze from chemistry, the presence of transition metals, and the choice of fluxing oxides used to melt the glaze. The exact change in organization of electrons in the color centers of a ceramic glaze affected by ionizing radiation is not particularly well understood by science. I recommend testing fired glazes with different flux compositions and including a variety of transition metals if you wish to achieve interesting results not mentioned here.

We found that the color of crystalline features and most types of variegation effects remained unchanged after radiation exposure. As a result, there is an interesting potential for the use of this technique as an alternative to strike firing for macrocrystalline pottery or as a way to increase contrast and visual intrigue in variegated glazes.

Dispelling Fears, Expanding Creativity

Hamideh and Wilson worked to assuage my fears about radiation. “As health physicists,” says Hamideh, “we strive to keep radiation exposure as low as reasonably achievable and that no radiation exposure should be received without a net societal benefit.”

“Radiophobia is real,” adds Wilson. He reminds us, “Pretty much everything is radioactive. Stars, people, walls, earth; we all irradiate each other, but know that bananas, medical x-rays, and nuclear bombs are not equivalently radioactive. Just like fire, radiation has many extremely good uses. However, a general fear of the word radiation has thwarted efforts to learn more.”

“If our research stays in our field forever,” Wilson explains, “few would benefit from it. Art involving science could really help ameliorate the misunderstandings and confusion involved in the general public’s opinion of nuclear science.” Just as science can be celebrated through the pursuit of art, so can science enrich our quest as artists to capture and reflect beauty around us as our eyes see it.

If you are interested in experimenting with this technique on your own, there are more than 40 companies across the US that offer affordable irradiation services to the general public. Commercial food irradiation only costs between 8–10 cents per pound, but many companies have an unreasonably large minimum order. FTSI irradiation services (http://ftsi.us/irradiation) in Mulberry, Florida, offers pricing based on package size and dose strength. Because of the penetrating nature of gamma radiation, the materials need not be removed from the package for processing. An absorbed dose of 15–30 kGy should induce a color change.

the author Mike Stumbras is a functional potter from Chicago, Illinois. He has completed residencies in four states and is currently a MFA candidate at Louisiana State University in Baton Rouge, Louisiana.