Jennifer F Boyer on thu 28 mar 02
Hi All,
I'm testing a glaze revision that Ron Roy did for me to
eliminate crazing on a new clay body. The new glaze has passed
the test: I put the pots in the freezer for 24 hours and plunged
them into boiling water straight from the freezer. I repeated
this 3 times. No crazing. My question is: does this test show a
thermal shock toughness in the clay as well, or is the 212
degrees of boiling water too low to stress the clay enough. I
figure the clay is going from 0 to 212 degrees in a short time.
That is less of a temp difference than 68(room temp) to 350
degrees(oven temp), but still pretty dramatic.
What do you think?
Jennifer, about to SWITCH clay bodies..... OHboy
--
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
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/
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
John Hesselberth on thu 28 mar 02
on 3/28/02 8:27 AM, Jennifer F Boyer at jboyer@ADELPHIA.NET wrote:
> Hi All,
> I'm testing a glaze revision that Ron Roy did for me to
> eliminate crazing on a new clay body. The new glaze has passed
> the test: I put the pots in the freezer for 24 hours and plunged
> them into boiling water straight from the freezer. I repeated
> this 3 times. No crazing. My question is: does this test show a
> thermal shock toughness in the clay as well, or is the 212
> degrees of boiling water too low to stress the clay enough. I
> figure the clay is going from 0 to 212 degrees in a short time.
> That is less of a temp difference than 68(room temp) to 350
> degrees(oven temp), but still pretty dramatic.
> What do you think?
> Jennifer, about to SWITCH clay bodies..... OHboy
Hi Jennifer,
That test will show one aspect of thermal shock resistance. Certainly it i=
s
a good one for teapots and the like. It tests for clay/glaze fit (crazing
and/or dunting/shivering). Another aspect though is whether or not your
fired body has any cristobalite in it. Cristobalite causes problems when it
goes through a phase transition at 226=B0C(439=B0F). You might test for that b=
y
heating it in an oven to 450 or 475. Then take it out and set it on your
counter-top. Obviously this is a test that requires great care.
The dinnerware industry uses an even more aggressive test for clay/glaze fi=
t
than the one you used. It is detailed in an ASTM procedure that is
referenced in our book. It basically involves heating in an oven and then
plunging the pot into room temperature water. If I remember correctly, 350=B0=
F
is the maximum temperature they use.
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.co=
m
Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Jennifer F Boyer on fri 29 mar 02
Thanks John, This info is exactly what I was looking for. I'll
go torture my pots some more! I'll use my old claybody and the
new one too in these tests, to have something to compare the new
one to.....
John Hesselberth wrote:
>
> on 3/28/02 8:27 AM, Jennifer F Boyer at jboyer@ADELPHIA.NET wrote:
>
> > Hi All,
> > I'm testing a glaze revision that Ron Roy did for me to
> > eliminate crazing on a new clay body. The new glaze has passed
> > the test: I put the pots in the freezer for 24 hours and plunged
> > them into boiling water straight from the freezer. I repeated
> > this 3 times. No crazing. My question is: does this test show a
> > thermal shock toughness in the clay as well, or is the 212
> > degrees of boiling water too low to stress the clay enough. I
> > figure the clay is going from 0 to 212 degrees in a short time.
> > That is less of a temp difference than 68(room temp) to 350
> > degrees(oven temp), but still pretty dramatic.
> > What do you think?
> > Jennifer, about to SWITCH clay bodies..... OHboy
>
> Hi Jennifer,
>
> That test will show one aspect of thermal shock resistance. Certainly it i=
> s
> a good one for teapots and the like. It tests for clay/glaze fit (crazing
> and/or dunting/shivering). Another aspect though is whether or not your
> fired body has any cristobalite in it. Cristobalite causes problems when it
> goes through a phase transition at 226=B0C(439=B0F). You might test for that b=
> y
> heating it in an oven to 450 or 475. Then take it out and set it on your
> counter-top. Obviously this is a test that requires great care.
>
> The dinnerware industry uses an even more aggressive test for clay/glaze fi=
> t
> than the one you used. It is detailed in an ASTM procedure that is
> referenced in our book. It basically involves heating in an oven and then
> plunging the pot into room temperature water. If I remember correctly, 350=B0=
> F
> is the maximum temperature they use.
>
> Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.co=
> m
> Email: john@frogpondpottery.com
>
> "The life so short, the craft so long to learn." Chaucer's translation of
> Hippocrates, 5th cent. B.C.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
--
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
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/
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
| |
|
