Nancy Galland on fri 20 oct 00
In response to the statement that al whate clays are robably ball clays, I
asked if pure porcelain, which does not contain ball clay according to my
supplier, is also a ball clay. This is the relply I received:
Hi Nancy,
It's my understanding that porcelin dishware is made largely, if not
entirely, from kaolin - at least that seems true for slip-poured porcelin
china. Kaolin for china is mined mostly in Georgia. I know that the kaolin
folks went through their own dioxin scare a number of years ago and that
they began testing at that time. Believe it or not, there is a Kaolin
Association that has a web site that can be contacted about this issue. You
could also ask your kaolin supplier to provide some testing info.
Ball clays seem to be used in stoneware clay mixes and "sanitary ware" -
sinks, toilets and the like. I wouldn't be surprized, though, if ball clay
was added to some porcelin pottery mixes where the clay is intended to be
wheel thrown, as pure kaolin seems to be too difficult for most folks to
work on a wheel.
I'm not aware of a list of clays that have been tested for dioxins. Most of
the problem seems to be centered on ball clays, however, we still don't know
why or how they have come to be contaminated. It's possible that these
dioxins date from the time when the clay was deposited - 35 million years
ago - since we can find no evidence of human sources.
-John C. Matheson, FDA
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