Joseph Herbert on sun 12 aug 07
The mineral Talc and the minerals that make up Asbestos generally have the
same sort of geologic history, metamorphosis of preexisting rock under heat,
pressure, and active chemical solutions and so are often found together. As
with any mineral deposit, purity is a relative concept. The idea of a
"pure" mineral deposit could, at best, only be applied to a single crystal
of something. There have been single Beryl crystals of substantial size
(weighing several tons) found that could considered a pure deposit, but that
is rare. All mined bulk "minerals" are actually rocks, that is, a naturally
occurring combination of minerals. Sometimes the percentage of one mineral
can be very high and so we think of "pure" deposits. It is never 100% and,
while processes that can remove contaminates exist, they are generally too
expensive for use except in the case of metal ores. Coal, for example, is
often mostly carbon but there is also Iron Pyrite (Iron Sulfide), a
significant source of Sulfur dioxide in the air, and some arsenic and enough
silica to make fly ash and cinders.
That being said, the presence of other minerals in talc is not surprising
and the fact that those minerals could be asbestos components is less
surprising still. While I have not followed the research in the progress of
Mesothieloma, I seem to recall that there was some thought that the shape of
the particles was a key component of development of the disease.
(Interesting to call it a disease since it is an industrial injury of the
most insidious kind) In any event, I think that the indication now is to
avoid inhaling any needle-like insoluble crystal or particle. Just what the
composition of the little needles is may not matter so much as long as they
keep their shape in the lungs and move, and scar, and move, and scar....
So, we are back to the constant common potter's problem of combating dust.
Asbestos never caused many problems (that we know of) until it was adopted
as an industrial feedstock for hundreds of products. Particularly the use
of the material, in a finely divided state, as filler in insulation, tiles,
and other building products. Its use in sprayed-on insulation has been
particularly tragic for shipyard workers and in the construction trades. In
school situation where the art teacher may not be (as we have heard in
recent discussions) as informed might be desirable in all things ceramic,
using a talc clay body that may contain up to 50% talc by weight seems an
unnecessary risk to the young. These days elementary art teachers are often
working under less than desirable conditions, not having their own room,
spending relatively little time in a particular place, and sometimes leaving
cleanup to persons even less conversant with the problems of clay dust.
What the pursuit of whiteness in clay products does for (to) us. Would not
a red firing earthware be more plastic, cheaper to buy, and easier to fire?
But it isn't white.
Joe
Joseph Herbert
Technical Writer
Irving, Texas
214-725-8305 (Cell)
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