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leaching question (cobalt and others)

updated sat 7 mar 98


John Baymore on fri 6 mar 98

Hi folks=21 Wow....... haven't posted on CLAYART in a long while. =

Do you know of a source book or article where I can read further on
leachability levels of cobalt (and other metals) and what is harmful? I was
thinking and curious about healthy amounts of trace metals and how this
relates to clay pots and the leachability issues.

For instance: cooking in cast iron ware is supposed to be healthy for you
because of the small amounts that the pot or cookware releases.

What is the threshhold level of cobalt for humans? What amount is ok if


Leaching of anything is a complex subject, and a bit important if you make
functional ware for sale to the public. Also important if you teach others
to make functional ware.....both ethically and legally. I think schools
should be at the forefront of researching and disseminating information on
this issue.

Not a lot of studies have been done (in this country) on leaching of metals
specifically in relation to =22art / craft=22 pottery. Some industrial =
focusing mostly on the leaching of those materials regulated by the FDA
(lead and cadmium) have been done.

The =22we've been using it for years and haven't had a problem=22 and =22I =
know a
guy who has been using it and he's 98 years old and healthy as an ox=22 and
=22xxxxxxx have been using pots glazed with xxxxxxxxx for years and they are
fine=22 approaches to (supposedly) establishing the relative safety of a
specific material are somewhat misleading........... at one point that
situation was true of lead, for example. We now know lead leaches out of
improperly formulated, applied, and/or fired glazes and that small levels
do significant harm.

The complexities of such things as the synergistic effects of different
toxic materials in a person's body, total body burden, risks imposed by
other unrelated illnesses, multiple sources of exposure, genetic
predisposition factors, and the like make studying this stuff an incredibly
difficult (and expensive) proposition.

The answer to the =22how much is OK=22 question for most of the metals used =
ceramics is pretty much .......=22no one really knows for sure=22. No one =
done much in the way of clinical studies of this subject on most stuff
......... it is a pretty narrow focus field. Plenty of other more pressing
subjects for the research dollars.

As to lead and cadmium, there are specific FDA standards that are written
into law and which apply to all potters (California has additional more
stringent laws).

Monona Rossol (see below) promotes the use of the EPA drinking water
standards as a good basis for comparison (for a 24 hour leach test) lacking
any specific studies and government regulations. Seems pretty reasonable
from a moral standpoint, and probably a good defense in a potential product
liability case =3Cwg=3E.

Basically speaking, I think that without definitive data proving the
contrary, one should assume that a reasonable standard of care should be
exercised with all materials. If there is a substance that could leach out
that has some known toxic properties on ingestion (this information is more
readliy available)...... then you might want to carefully consider how you
are using it in your functional ceramics. To not do so seems morally
irresponsible and possibly legally inadvisable.

That =22reasonable standard of care=22 is the phrase that lawyers will spend
hours (and fortunes) debating in a product liability suit =3Cg=3E.

Contact Monona Rossol, MS., MFA, industrial hygenist at ACTS (Art, Craft,
and Theatre Safety 181 Thompson St. =2323, Ny NY 10012-2586), for some =
information on leaching issues. She can also probably give you references
for more technical sources of information. She is one of the top two
experts in the field of health and safety in the arts. Just happens to
have an MFA in ceramics to boot =3Cg=3E, so clay is near and dear to her =
She can be reached at 75054, or at 212-777-0062. Web
site at is also available.

The other expert would be Dr. Michael McCann, who wrote =22Artist Beware=22.
He was based out of the Center for Safety in the Arts also in NYC, but I am
not sure if he can still be reached there. That book has some good
information also.

There probably are some expert ceramic engineers specalizing in glaze
leaching issues out there in the industrial world also.



John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA