Marianne Lombardo on sun 26 nov 00
If I glaze and fire stoneware to cone 6, can it go into both a microwave =
as well as a conventional oven?
John Hesselberth on tue 28 nov 00
Marianne Lombardo wrote:
>If I glaze and fire stoneware to cone 6, can it go into both a microwave
>as well as a conventional oven?
>
Hi Marianne,
The answer is: it depends. The key to microwave safety for a pot is
whether or not the clay is vitrified. If it is not well vitrified it
will absorb water through normal use--dishwashing in particular. That
water will then heat up rapidly in the microwave and the pot will get
VERY hot. Too hot to handle safely. Here is a way to check your pot.
Put a cup in a pan of water so the cup is fully submerged; simmer for two
hours. Your family might think you've gone bonkers, but just ignore
them. The purpose of this step is to get the clay to absorb as much
water as it can. Let the pan/pot cool to room temperature with the pot
still submerged. Dry the pot. Take another pot, that you know is
microwave safe and nearly fill it with room temperature water. Put both
pots in your microwave--the one filled with water and the dry, empty,
test pot you have boiled.
Turn your microwave on for 10 seconds at a time. After each cycle
CAREFULLY touch the empty pot. If you can touch it without it feeling
too warm to pick up proceed to another cycle. Repeat until the water in
the other pot starts to boil. If you can still pick up the empty pot
without it being uncomfortably hot, your pot is microwave safe.
Please be careful in doing this experiment. If your boiled/dried pot
gets very hot stop the experment immediately and resolve to find a clay
that is better vitrified at your firing temperature (or increase your
firing temperature). If a clay has absorbed several per cent water it
can actually crack or blow apart in the microwave when that absorbed
water suddenly turns to steam.
As you might surmise, earthenware pots are seldom useable in the
microwave. The only way they can be safe is if they are completly
encased in a very stable glaze. Unfortunately, not all clays rated at
cone 6 by their manufacturer are well vitrified either. It seems that
you have to get water absortion down to 2-3% or below before a clay is
microwave useable.
Good luck on your testing. John
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
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