Marcelyn Havens on wed 21 apr 04
First off, a special thanks to everyone who answered my first time kiln
owner question. Charles, I've ordered the book you suggested and am
looking forward to mastering those cone 6 glazes... thanks for the
recommendation.
On to question number 2. My first few firings have gone pretty well,
nothing to write home about but some pleasant results and some not so
pleasant. All part of the learning process I know. Today I was in the
ceramic store and was trying to solve the problem of my transparent
glaze crazing. I am firing my next load to a higher bisque cone (I had
done 06, I'm moving to 05 or 04) but one comment made was... "are you
matching your clay body with your glaze?" Well duh.... I would if I
knew how. So being the inquisitive person I am, I asked how to do that
and they couldn't tell me. Said the resident potter wasn't there and
they didn't know.... so I'm left high and dry as I don't plan on
heading down to the inner loop of Houston any time soon. Anyone have a
simple explanation for me?
Anyone interested in seeing some of my very first results (be kind, I
truly am a newbie.... haven't mastered anything over 10 inches high!
augh! *grin*) http://home.swbell.net/khavens/pottery.html
Marcelyn, who has enjoyed reading everyone's signing issues and
personalized signatures.
Houston, TX - by way of many places
Ron Roy on thu 22 apr 04
Hi Marcelyn,
Send me the recipe for the crazing glaze - and tell me how much cone 6 is
bent in you typical firings. Tell me how far apart the craze lines are as
well.
I can probably adjust that glaze for you.
RR
>First off, a special thanks to everyone who answered my first time kiln
>owner question. Charles, I've ordered the book you suggested and am
>looking forward to mastering those cone 6 glazes... thanks for the
>recommendation.
>
>On to question number 2. My first few firings have gone pretty well,
>nothing to write home about but some pleasant results and some not so
>pleasant. All part of the learning process I know. Today I was in the
>ceramic store and was trying to solve the problem of my transparent
>glaze crazing. I am firing my next load to a higher bisque cone (I had
>done 06, I'm moving to 05 or 04) but one comment made was... "are you
>matching your clay body with your glaze?" Well duh.... I would if I
>knew how. So being the inquisitive person I am, I asked how to do that
>and they couldn't tell me. Said the resident potter wasn't there and
>they didn't know.... so I'm left high and dry as I don't plan on
>heading down to the inner loop of Houston any time soon. Anyone have a
>simple explanation for me?
>
>Anyone interested in seeing some of my very first results (be kind, I
>truly am a newbie.... haven't mastered anything over 10 inches high!
>augh! *grin*) http://home.swbell.net/khavens/pottery.html
>
>Marcelyn, who has enjoyed reading everyone's signing issues and
>personalized signatures.
>Houston, TX - by way of many places
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Hendrix, Taylor J. on thu 22 apr 04
Marcelyn:
Not a dumb newbie question either. From one newbie to another, the
solution is not hard to understand.
Everything changes in size when it is heated or cooled. Glazes and clay
do it. They both expand when they get hot and contract when they cool.
Not so much a problem when everything is all melty soft (<--technical
pottery term), but when things start to get stiff... Crazing is the
result of UNEVEN contraction between the glaze and the pot. The glaze
actually contracts more than the body does and the cracks help relieve
the stress of a 'small' glaze on the body. You need to add ingredients
to the glaze that will make it contract less on cooling. It's as if Mr.
Pot in his vanity tried to put on the tux that he wore to his high
school prom. That being 20 years ago, you can imagine what happened
when he bent over to pick up Nelly Parson's cell phone that she dropped
in the middle of the dance floor.
Many general books on glazes will explain all this to you and give you
several ways to remedy this. One thing you might try is adding some
silica to the glaze. Silica (melted) doesn't expand/contract as much as
other ingredients. Remember though, add stuff changes stuff and may
change more than just the expansion/contraction of your glaze.
Man! I sure hope I got that stuff right. I'd really hate it if David
H. had to call me down in public. You know he pantsed me one year in
front of the Hatcher's booth at Gruene, TX. Watch him.
Taylor
Waco, Texas, USA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Marcelyn
Havens
Sent: Wednesday, April 21, 2004 8:02 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Not a dumb gallery question, but another dumb newbie question
...
one comment made was... "are you
matching your clay body with your glaze?" Well duh.... I would if I
knew how. So being the inquisitive person I am, I asked how to do that
and they couldn't tell me. Said the resident potter wasn't there and
they didn't know.... so I'm left high and dry as I don't plan on
heading down to the inner loop of Houston any time soon. Anyone have a
simple explanation for me?
...
Snail Scott on fri 23 apr 04
At 08:01 PM 4/21/04 -0500, you wrote:
>...one comment made was... "are you
>matching your clay body with your glaze?" Anyone have a
>simple explanation for me?
If you are working with commercial glazes, the simple
method is trial and error. With glaze-calculation
software, you can find a recipe that's more suitable.
The essence of the problem is 'Coefficient of Expansion',
more soecifically, the shrinkage that occurs during
cooling. If the glaze still has further to shrink than
the clay body at the point when the claze becomes solid
and brittle, it will have to crack ('craze') to encompass
the now-larger clay (larger relative to the glaze, that
is).
Glaze software will allow to you find the 'CoE' of any
given glaze recipe. Finding the CoE of the clay is harder,
but if a given recipe is crazing on your clay, then you
know you need a glaze with a lower CoE. It's usually
easiest to pick a preferred clay, then match a glaze to
it, than to try to change clays to match a glaze.
If you don't have software, (and don't want to do the
math by hand) or don't want to mix glazes from scratch,
simple trial and error works, too. Just mix up a lot of
recipes (or buy a lot of small jars of commercial glaze),
and make tests.
-Snail Scott
still in Reno, NV USA
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