Karl P. Platt on wed 9 apr 97
Subject: Re: Ba leaching (long and picky)
From: Bill Walker
>>I suspect that BaSiO3 is not the only crystalline barium compound
found in glazes, considering the wide range of formulations that
people might try.<<
Others are (thermodynamically speaking) a lot less likely to be seen.
Formulations vary more in style than substance. The palette of elements
present in potter's glazes is, in fact, quite limited. BaSiO3 is, in a
large majority of cases, far more likely than any other combination one
might find.
>>agitating would increase the release rate<<
Significantly.
>>Food is frequently stored or cooked in ceramic containers.<<
Cooking is of far greater concern that storage. The (already slow)
reaction rates are retarded by low temperatures and elevated at high
temperatures. This is particularly true for the case of Ba as has been
noted in an earlier posting.
>>Potters often use barium because of its influence on color and texture <<
So?
--
>when used in large amounts it produces beautiful effects that would
>not be considered appropriate for chemical vats or the food processing
>industry where a smooth, usually white surface is desirable.
The glazes in question which I made were colored using a Cr-Fe-Zn stain
-- if I recall it was Pemco's GS-514 (which makes a very cool orange in
high ZnO glazes). Mason's Saturn Orange is of the same class of
pigments.
>Out of the Millions of items of trouble
>free tableware made by US producers, the only documented cases of
>leaching problems (poisoning) have been with foreign products.
>>Because the importers did not have the stuff tested!
>>And probably did not know that they should!
Of course they didn't and it's not that they didn't know -- they didn't
care. And the US makers get penalized with the burden of yet more
regulatory overhead that increases consumer costs without providing any
measurable benefit -- remember there wasn't and hadn't been a problem
with the US made goods.
>>But you still have to test!
For what and why? There is _no_ Ba leaching standard because there is no
Ba leaching "problem". It doesn't exist. Nco Existe!
No one in the history of humanity has become ill from Ba leached off of
a dinnerplate or coffee cup. The odds of having anyone taken ill by a
plate with Ba bearing glaze on it are about the same as winning the NY
State Lootery -- er, lottery.
>>Are you suggesting 0.02 ppm as the safe level?
I made no such suggestion. This is, however, no less arbitrary as any
other standard that has been suggested. Note that 0.02 ppm is equivalent
to .02 grams in a metric ton. This would exist in most places as a
consequence of nature. But then didn't I hear the EPA was looking for a
way condemn God for putting it there in the first place -- this is their
secret plan for dealing with the Federal Debt. They're going to sue God
for all he's got and we'll all get rich.
>>The extreme cases being those glazes that release 3000ppm that no one
>>ever tested because someone doubted, was ignorant of or chose to >>ingnore the
Please, please, please forward to me by FAX 55.48.234.0059 any and all
details as to this incident including the name and address of the person
who was taken ill, their physician, and the potter so that I can verify
these utterly historic precedents for our collective posterity. I am
also extremely interested to see the formula and firing conditions used
to make this glaze.
>>Or are we only considering glazes that are in thermodynamic
equilibrium?<<
Nothing is in equilibrium --- for long -- Entropy happens.
Karl P. Platt -- still extremely worried about the pernicious presence
of Dihydrogen monoxide and hovering over the Fax machine.
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