Jennifer Boyer on thu 2 mar 06
Hi all,
So I did an absorbency test on my white stoneware to eliminate that
as a variable in my quest to find out why some of my iron red glazes
get hot in the microwave.
I took test pieces out of the still warm kiln and boiled them for 90
minutes, then let them cool in the water. I wiped them off to get rid
of surface water. One test showed no change of weight and one 85.4
gram piece went to 85.6 grams. So we're talking about a claybody that
doesn't absorb much moisture at all, right? I had 2 tests in the kiln
with cones next to them: one went to cone 10 down and one went to
cone 10 bending, which is about the coolest I fire.
I still get the very hot results when heating the Bailey's Red mug in
the microwave. I got some more Anderson Ranch mugs out of this firing
that have a low iron liner. These get warmer than the non iron glazes
I have using the same clay body but the heat is touchable, unlike the
Bailey's mug.
One interesting thing is that I mixed up another set of tests(secret:
my assistant did them: gotta love her)) mixing Bailey's and Anderson
with regular iron oxide and synthetic iron oxide.
These tests were extruded cylinders dipped in glaze, so the inside
and outside were glazed with the test glaze. This is unlike the mugs
which all have non iron liners. The test pieces got quite a bit
hotter than the mugs, which had no water in them but were in the
microwave with a different mug with water in it. The Anderson still
got hotter than the Bailey and the Synthetic iron glazes seemed to
get hotter than the regular iron ones.
My current theory: I think it may have to do with glaze thickness and
the ratio of iron glaze to pot thickness. I guess if I wanted to go
overboard I could do some careful measuring of SG and then do some
mixes of each glaze that vary the SG. My test pieces are extruded so
they are pretty uniform. The only variable in the tests would be bisk
temp and glaze thickness.
But I think I give up at this point. I'm just glad the Anderson Ranch
Red isn't scorchingly hot in the microwave, so I feel I can sell it
without a warning.....
See some of you at NCECA!
Jennifer
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Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
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