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