Linda Pahl on sat 21 feb 04
Mildred Herot wrote:
> Hi Linda: Reading your message brought to mind a question I would
> really
> like answered. I like to layer glazes and usually brush and stipple a
> glaze
> on greenware and, after the bisque, spray on another glaze for the
> mix. If
> the second glaze is a safe one, will that negate the problem with the
> first
> if the first is not food safe? Hope I made myself clear.....Mildred
> Herot
Hi, Mildred,
I wish there were a definitive answer to this question, however, my
instinctive short answer would be a qualified "maybe". I would think
that if you applied a stable second glaze over an unstable first glaze
in an even and fairly thick application the result should be a stable
finish. Still, though it would seem logical that a stable glaze
covering an unstable one would mitigate any problems with leaching I
think the only way to be positive is to send a sample of glazed ware to
a lab to be tested.
Since I am fairly new to the world of glazes beyond strict recipes, I
hope that John Hesselberth or Ron Roy, or any of clayarts other glaze
gurus will elaborate further on this.
Regards,
Linda Pahl, Kew Gardens, New York
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email: TheClosetPotter@earthlink.net
website: http://home.earthlink.net/~jessieadair/tests/
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John Hesselberth on sat 21 feb 04
On Saturday, February 21, 2004, at 01:31 AM, Linda Pahl wrote:
>> I like to layer glazes and usually brush and stipple a glaze
>> on greenware and, after the bisque, spray on another glaze for the
>> mix. If
>> the second glaze is a safe one, will that negate the problem with the
>> first
>> if the first is not food safe? Hope I made myself clear.
Hi Mildred/Linda,
It definitely can help--the only question is how much. I have only done
a couple reasonably well designed experiments in this area and a coat
of a stable clear glaze on top of a leacher cut down the leaching by a
factor of 5-10. Quite a bit in those experiments. But would it do it
with every glaze combination--I have no idea. It is going to depend on
how stable the stable glaze is, how thick the coating of it is, and how
much opportunity those glazes have to intermingle during firing (say
during a long soak at peak temperature). Every situation would have to
be tested. The obvious better answer is to use stable glazes on
functional surfaces and then not have worry about it. I am fairly
certain that 2 stable glazes combined by layering or whatever will
always result in a stable glaze.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
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