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glaze toxicity (fwd)

updated mon 31 mar 97


Monona Rossol on sat 29 mar 97

Kris Baum wrote:

> I am also concerned about potential liability. And I don't have the
> financial resources to do leach testing on every glaze nor to carry
> liability insurance (at least, until I start making a profit.) <

The maker or manufacturer is always liable for damages if any product
causes a consumer harm (unless the consumer deliberately abuses the object).
But if the maker or manufacturer can show that they did everything reasonable
and possible to insure that the object was safe, then at least, they will
only be liable for the actual damages proven by the injured party. No
additional punitive damages can be assessed.

But if the jury hears during the trial that 1) the potter had heard that
there might be a hazard from their glazes; 2) they chose to do absolutely no
testing of the potential hazards of the glazed ware they sold, NOW, not only
are damages in order, but so are **punitive** damages. The potter clearly
did not exercise due care.

Punitive damages also must be paid directly out of the pocket of the maker.
They do to manufacturers (large and small) what they did to Simpson. They
take a look at their financial worth and make a judgement about what is
proper. And no insurance company is allowed to write a policy to protect
anyone from punitive damages.

It is also important to realize that meeting a regulation--that is only
avoiding lead and cadmium because they are regulated by FDA--does not protect
your liability. Even if you meet every single law and regulation regarding
your product, it if injures someone, you pay. After all, it wasn't the
consumers fault.

On the other hand, if the potter goes into court with at least SOME test
results showing that they tried to quantify the problem and use safer glazes,
then the potter has demonstrated a degree of due care. I would consider
the cost of those lab tests as payments on a sort of "insurance" policy.

> If a published recipe says that it is food-safe, can that be relied upon?<

Not a recipe or a product label can be leaned on heavily. Some of you
should remember that only a couple months ago a Maine potter got a visit
from FDA and found her carefully fired "Food Safe" labeled commercial glazes
flunked. The glaze distributor just showed FDA their glaze manufacturer's
test results and claimed that the potter must not have done a good job of
application or firing.

However, as someone who has been writing expert opinions on labeling issues
for an up-coming trial all last week, let me offer one more opinion:

Not including information about all the variables and not advising users of
the glazes to test their ware regularly could be construed as "failure to
warn." For an individual with limited funds, I would probably write that
opinion for free just to get better labeling out of the ceramic industry.

As for an article or book whose text includes the claim that a certain
glaze is "food safe," the claim may be actually easier. Publishers are now
being sued for damages when their authors make mistakes or even omissions in
advice that result in harm. You should see the fancy wording on my more
recent book contracts by which my publisher transfers that liability to me.

> And if one tinkers with the glaze a little (e.g., like upping the lithium
> carb from 1 to 1.5%, or substituting whiting for strontium carbonate),
> does that invalidate the presumption of non-toxicity? <

If you alter a commercial glaze in even the tiniest way, the manufacturer's
warrantees are all void. I would assume the same with a published recipe.

> How are others handling this issue? Are we only free from litigation if
> we limit our glazes to commercial glazes that are rated food-safe? <

Again I say for emphasis, you are not protected by using Food Safe glazes.
Manufacturers can claim you did something wrong. And some Food Safe glazes
now say in small print that ware should be tested.

I suspect that there will be even more label changes if the case I am working
on currently has the effect I hope it will.

Monona Rossol, industrial hygienist
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York, NY 10012-2586 212/777-0062

Monona Rossol on sat 29 mar 97

Ric Swensen wrote in part:
"great mysteries" of toxicity.

> I would encourage some of our ceramics school that have chemistry
> departments to sponsor research. The Society of Glass and Ceramic Decorators
> and the American Ceramic Society, surely have done much work in studying
> dinnerware and release of potentially harmful "stuff"<

Could agree with you more!!! I have actually embarrassed representatives of
Alfred with this idea in public lectures.

>...and if a student could be interested in developing a reliable test for
> toxicity for potters glazes and bodies, or some light could be shone into
> this great deep black hole....<

They wouldn't even need to develop a "test." The tests are already in place
and the equipment is in the Chemistry Departments. The only thing they have
to do is plan which glazes they are going to test and for which variables
(e.g. different firing temperatures, variations in oxidation/reduction
balance, etc.).

> that could be a great service to us all. <

And aren't "services to the field" what educational institutions should be
providing? You damn bettcha.

Thanks for making my day, Ric.


Monona Rossol, industrial hygienist
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York, NY 10012-2586 212/777-0062

Monona Rossol on sat 29 mar 97

More good ideas from Ron Roy,

> I'll start a list of materials that I know are safe to use in a relatively
> balanced glaze. I wish I could say any glaze but there are certain oxides I
> think can be a problem like Boron and Zinc. I have no objection to being
> corrected. I know Boron is a "soft" material so you need some skill to use
> it or it could come out of glazes. If you are low firing you have to use it
> - even at cone 6 it is a very useful flux (oops - I promised myself not to
> get into that one.) <

I would worry about boron though. Soluble boron compounds are used as wood
preservatives and pesticides. They are not as toxic as other pesticides, but
the EPA drinking water quality standard for it is 0.6 ppm.


> All clays except Barnard (Black Bird) which has a fair bit of MnO2.<
> Bentonite.
> All feldspars including Cornwall Stone and Neph Sy.<
> Silica
> Whiting
> Tin oxide <

These are all probably safe, but get MSDSs anyway to check to be sure that
the manufacturer or Mother Nature has not given you a surprise. Many
mineral deposits of calcium carbonate (whiting), for example, contain lead.
This is why dietary supplements of inorganic calcium list the lead content
on the label.

> Zinc Oxide? <

It would take a LOT of zinc to cause a problem. I'd probably do a couple of
tests and than compare with the RDI (Reference Daily Intake).

> Frits 3110, 3124, 3134, 3195, 3278, 3269. (there are many more but these
> are the ones I use - all have some boron.)<

Then I'd test.

> Iron oxide, Rutile and Titanium Dioxide
> Dolomite

Again get the MSDS. Rutile is usually quite impure. Dolomite also often
contains lead. Hopefully well below the reportable 0.1 % which must be
reported on MSDSs.

> Gerstely Borate <


> Talc
> Wolastonite
> Zircopax <

Check MSDSs

> Strontium Carb (has a small amount of Barium 1to2%) <


> Magnesium Carb
> Bone Ash
> Soda Ash (soluble) <

Check MSDSs

> Encapsulated stains? <

Never trust them. Always test if they contain toxic metals. These things
are very stable with respect to heat, but that says nothing about how stable
they are with respect to acid either in the powdered state or once fired in a

> I think small amounts of Cobalt (under 0.5 %) and (Copper 2% or less) are
> OK but there are some glazes that would give them up I am sure. <

Yup. Copper's drinking water standard is 1.3 ppm, but it was set for taste.
It takes a little more than that to be toxic so you've got a bit of
leeway. Cobalt has no standard in drinking water--probably because it is
almost never there. But it is very toxic and a suspect carcinogen. I think
I'd test.

> If you can't make a decent liner glaze from the above it's your ability to
> make glazes that needs improvement. Get smarter or hire someone to do it
> for you.<

Good advice. My column in the next (summer issue) Clay Times should cover
how a former Clayart subscriber searched your library for cone 6 glazes with
only a short list of materials I suggested. She found about 7, made
experimental batches and tested them. This is not a big deal.


Monona Rossol, industrial hygienist
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York, NY 10012-2586 212/777-0062