Janet H Walker on thu 8 jan 98
Judith Enright reported:
In talking with Ann in the lab at the Mason stain company this
morning, she insisted that their colors are foodsafe to ^10 in
oxidation, ASSUMING THAT THE BASE IS BALANCED AND FIRED CORRECTLY.
Just wondering. Did you ask her if they had any test results that
you could see?
At NCECA, there was a display from a company that sold glazes marked
as foodsafe. I asked the representative what kind of testing they
did on their glazes. They gave me a funny look. "Testing?" Yes, I
said, in order to demonstrate the safety. "Well," they said, "we
don't have to test them because they are fritted." So I made a note
of the conversation on the brochure from that company. (Sorry,
don't have it with me. It was NOT the Mason company however.)
From what I've read, I'm not sure how any glaze company can tell you
what is safe and what is not since you could put together a set of
chemical circumstances in your glaze that they had no way of imagining.
(Note that Ann Mason's claim includes the warning that the glaze has
to be properly balanced and fired. This is the responsibility of
each of us, not of the company making the stain.)
The post from Tom Buck pointed out that manufacturers of
encapsulated stains say not to fire above 1250C (which is about ^7
by the way). This seems to suggest caution. Perhaps read the fine
print and then pay attention to its implications is the best policy.
I'm not maligning Mason here. I don't even know if their stains
have the same ingredient as Tom Buck's post is referring to. I'm
just saying that there's a clear puzzle here. Someone says "not
above ^7" and someone else says "fine to ^10". You then have to ask
why such a difference exists and do some investigation to clear up
the puzzle to your own satisfaction. Maybe the two sources are
talking about different technologies and that explains the different
recommendations. But until you know the reason for the difference,
isn't it best to stay cautious?
Jan Walker
Cambridge MA USA
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