Linda Fletcher on fri 19 jan 01
Antoinette wrote:
"Too often one find coarse unfinished bottoms on peoples work or glazes =
that
are not fully matured and burn ones hands in the microwave etc"
Would an under-fired glaze be the cause of burns ?=20
I would think that the high metalic content of a particular glaze would =
be the cause ???=20
I am always careful when I use any ceramics in the microwave, and =
always assume it will be hot.
I have also noticed that the same glaze on different clay bodies will =
react differently in the microwave.=20
I have guessed that it was a higher iron content in the clay that caused =
the heat.
My chemistry and/or physics education is sorely limited. Anyone more =
knowledgable have input on this ?
Linda
mudsinger in NH=20
Cindy Strnad on fri 19 jan 01
Clay pieces used in the microwave shouldn't be hot immediately upon removal.
Like any other substance, they will pick up the heat of the food after a
bit, but they shouldn't heat up on their own.
Heating can be caused by a couple of things. First, the clay may be too
permeable to water, and you may have a steam build-up in the walls. This can
not only cause burns, but could conceivably cause explosions.
Second, the glaze may be high in iron content. I have had this cause
excessive heating. I had no trouble with cobalt or copper in my experiments.
I'd say more, but I've submitted an article on this to Clay Times, and it
wouldn't be fair to them to send out the entire text of the article before
they print it. If you need more info now, post me privately and I'll be glad
to help all I can.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
John Hesselberth on sat 20 jan 01
Linda Fletcher wrote:
>Would an under-fired glaze be the cause of burns ?
>I would think that the high metalic content of a particular glaze would be
>the cause ???
> I am always careful when I use any ceramics in the microwave, and always
>assume it will be hot.
>I have also noticed that the same glaze on different clay bodies will
>react differently in the microwave.
>I have guessed that it was a higher iron content in the clay that caused
>the heat.
>My chemistry and/or physics education is sorely limited. Anyone more
>knowledgable have input on this ?
Hi Linda,
You will find quite a bit on this in the archives, but to summarize a
little bit of it. The primary cause of ceramic vessels getting too hot
in a microwave is unvitrified clay--clay that can still absorb water.
Earthenware vessels are a particular concern, but underfired stoneware or
porcelain can also be a problem.
Cindy Strnad has also shown that, in certain circumstances, high iron
content in a glaze can cause a problem, but that is her story to tell
(actually I recall that she just did less than a week ago).
Regards, John
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
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