Jennifer F Boyer on fri 5 apr 02
Well,
I tortured my pots(cone 10 ox ) and here are the results:
Test 1:
Froze pot for 24 hrs, then plunged into boiling water. Repeated
3 times
Result: No glaze crazing
Test 2: Heated pot in 350 degree F. oven for 1/2 hour and then
plunged into room temp water.
Result: Glaze crazing
Neither my tried and true glaze or my new glaze(for use on new
clay body) survived Test 2.
I wonder if anyone out there has tried Test 2 on stoneware? John
H said that it's a test that the ceramics industry uses....
I'm just happy they passed test 1,
Jennifer
--
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
Jennifer Boyer mailto:jboyer@adelphia.net
Thistle Hill Pottery
95 Powder Horn Glen Rd
Montpelier, VT 05602 USA
802-223-8926
http://www.thistlehillpottery.com/
Never pass on an email warning without checking out this site
for web hoaxes and junk:
http://urbanlegends.about.com/
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John Hesselberth on fri 5 apr 02
Hi Jennifer,
I went back and read the procedure (ASTM C554-93) again. While they do tes=
t
even up to 450=B0F they say that any whiteware that survives 3 cycles at 300=B0=
F
would not be expected to craze in normal service.
John
on 4/5/02 11:02 AM, Jennifer F Boyer at jboyer@ADELPHIA.NET wrote:
> Well,
> I tortured my pots(cone 10 ox ) and here are the results:
> Test 1:
> Froze pot for 24 hrs, then plunged into boiling water. Repeated
> 3 times
> Result: No glaze crazing
>=20
> Test 2: Heated pot in 350 degree F. oven for 1/2 hour and then
> plunged into room temp water.
> Result: Glaze crazing
>=20
> Neither my tried and true glaze or my new glaze(for use on new
> clay body) survived Test 2.
> I wonder if anyone out there has tried Test 2 on stoneware? John
> H said that it's a test that the ceramics industry uses....
> I'm just happy they passed test 1,
> Jennifer
> --
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.co=
m
Email: john@frogpondpottery.com
"Art is not a handicraft, it is the transmission of feeling the artist has
experienced." Leo Tolstoy, 1898
Gavin Stairs on fri 5 apr 02
Well, test 1 puts a glaze into compression. The result could be shivering
or dunting.
Test 2 puts the glaze into tension. The result could be crazing.
Neither of these tests is strictly a fit test. They are both shock
tests. A fit test assumes the glaze and body are the same temperature
always, but the temperature of both may vary over some range. Just the
heating or cooling portion of tests 1 and 2 are fit tests of this sort.
But ware in use is often subjected to thermal shocks, such as pouring
boiling water into a bowl, or taking a vessel out of the fridge/oven and
placing it on a stove top (a metal surface). The extreme case is embodied
in the tests indicated. A perfectly fitting glaze may survive test 1 but
fail test 2, and a glaze which passes test 2 by virtue of its
pre-compression may fail test 1 disastrously by shivering or dunting. This
is because of the large thermal coefficient of expansion of the materials,
not exactly the fit between them. A high thermal coefficient of expansion
will cause ALL vessels to fail one or the other of these tests most of the
time. The only way to get a consistent pass on both is to make ware with a
low coefficient of expansion which also fits with a slight glaze
compression after normal cooling (or heat treatment).
Gavin
At 11:02 AM 05/04/2002, you wrote:
>Well,
>I tortured my pots(cone 10 ox ) and here are the results:
>Test 1:
>Froze pot for 24 hrs, then plunged into boiling water. Repeated
>3 times
>Result: No glaze crazing
>
>Test 2: Heated pot in 350 degree F. oven for 1/2 hour and then
>plunged into room temp water.
>Result: Glaze crazing
>
>Neither my tried and true glaze or my new glaze(for use on new
>clay body) survived Test 2.
>I wonder if anyone out there has tried Test 2 on stoneware? John
>H said that it's a test that the ceramics industry uses....
>I'm just happy they passed test 1,
>Jennifer
>--
>~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
>Jennifer Boyer mailto:jboyer@adelphia.net
>Thistle Hill Pottery
>95 Powder Horn Glen Rd
>Montpelier, VT 05602 USA
>802-223-8926
>http://www.thistlehillpottery.com/
>
>Never pass on an email warning without checking out this site
>for web hoaxes and junk:
>http://urbanlegends.about.com/
>~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
>
>______________________________________________________________________________
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Gavin Stairs
Gavin Stairs Fine Editions
525 Canterbury Road
London, Ontario
Canada N6G 2N5
telephone: (519) 434-8555.
email: stairs@stairs.on.ca
Gavin Stairs Fine Editions is a small, desktop press specializing in book
design and fine, hand-made books.
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