Snail Scott on tue 13 sep 11
On Sep 13, 2011, at 11:58 AM, May Luk wrote:
> ...New studio mate moved in and found her glaze crazed at the new set up;
> same clay, same slip, same glaze. The most obvious difference from the
> last set up is the kiln; a smaller size kiln...
Might be quicker cooling, but might also not be the
exact same level of vitrification. One kiln's sitter or
controller is never equal to another's. Underfired clay
can cause crazing even if the glaze looks matured to
the same degree. Check the witness cones. If they are
really giving the same reading, try slowing the cooling
in the lower range (below red heat); just a tiny little bit.
Or add some extra top and bottom insulation to the kiln.
(Easier than doing the sides, and it still helps a lot.)
-Snail
May Luk on tue 13 sep 11
Hello all;
New studio mate moved in and found her glaze crazed at the new set up;
same clay, same slip, same glaze. The most obvious difference from the
last set up is the kiln; a smaller size kiln. The glaze is a cone 05
glossy and she was doing a "cone fire" program. What can we do to
compensate for the change so that this once trial-&-true glaze doesn't
craze.
Thanks
May
--
http://twitter.com/MayLuk
http://www.ceramicsbrooklyn.com/
May Luk on wed 14 sep 11
PS, bumping this up.
Any thoughts on:-
600 C - 550C - reversion of beta quartz to alpha quartz
220 C - reversion of beta cristobalite to alpha cristobalite
???
May
Brooklyn
On Tue, Sep 13, 2011 at 12:58 PM, May Luk wrote:
> Hello all;
>
> New studio mate moved in and found her glaze crazed at the new set up;
> same clay, same slip, same glaze. The most obvious difference from the
> last set up is the kiln; a smaller size kiln. The glaze is a cone 05
> glossy and she was doing a "cone fire" program. What can we do to
> compensate for the change so that this once trial-&-true glaze doesn't
> craze.
>
> Thanks
> May
>
--
http://twitter.com/MayLuk
http://www.ceramicsbrooklyn.com/
Ron Roy on wed 14 sep 11
Hi May,
Not sure what the question is but - the conversion of quartz at 573C
is quite sudden while the reversion of cristobalite is more gradual -
it is quite clear on the dilatometer charts.
RR
Quoting May Luk :
> PS, bumping this up.
>
> Any thoughts on:-
> 600 C - 550C - reversion of beta quartz to alpha quartz
> 220 C - reversion of beta cristobalite to alpha cristobalite
>
> ???
>
> May
> Brooklyn
>
> On Tue, Sep 13, 2011 at 12:58 PM, May Luk wrote:
>> Hello all;
>>
>> New studio mate moved in and found her glaze crazed at the new set up;
>> same clay, same slip, same glaze. The most obvious difference from the
>> last set up is the kiln; a smaller size kiln. The glaze is a cone 05
>> glossy and she was doing a "cone fire" program. What can we do to
>> compensate for the change so that this once trial-&-true glaze doesn't
>> craze.
>>
>> Thanks
>> May
>>
>
>
>
>
> --
> http://twitter.com/MayLuk
> http://www.ceramicsbrooklyn.com/
>
Ron Roy on wed 14 sep 11
Hi May,
As you know the clay/glaze interface may not develop well in low fire
- this may be the problem here.
Tell her to chose a slow fire ramp or better still make her own with a
slowdown to 50C per hour for the last hour of the glaze firing.
RR
Quoting May Luk :
> Hello all;
>
> New studio mate moved in and found her glaze crazed at the new set up;
> same clay, same slip, same glaze. The most obvious difference from the
> last set up is the kiln; a smaller size kiln. The glaze is a cone 05
> glossy and she was doing a "cone fire" program. What can we do to
> compensate for the change so that this once trial-&-true glaze doesn't
> craze.
>
> Thanks
> May
>
> --
> http://twitter.com/MayLuk
> http://www.ceramicsbrooklyn.com/
>
David Finkelnburg on wed 14 sep 11
May,
Bisque density may have changed so glaze application thickness may be
different, or final fired vitrification may be less, or both. A thicker
glaze has a greater tendency to craze (less alumina is dissolved from the
body into the glaze). Less vitrified clay body has less glass phase, thus a
lower CTE and more crazing. Adjusting the glaze or the firing(s) or both
appear appropriate.
Good glazing,
Dave Finkelnburg
http://www.mattanddavesclays.com
May Luk on wed 14 sep 11
Addendum:
After a little bit of correspondence with my studio mate, it
transpires that she used to bisque fire to cone 4 and now we are
bisque firing to cone 6 in the current smaller kiln. HA!
We will try out a slow firing ramp and especially slow from 1100 C
onwards. David Green did a very good explanation on this in his book
Understanding Pottery Glazes
Then my studio mate would have to bisque fire her wares to cone 04
like she always have done and we will see how it goes.
Thank you, Brains Of Clayart, for ALL your contributions and thinking
about the problem. I will forward all the answers to my very nice and
friendly studio mate.
May
Brooklyn NY
On Tue, Sep 13, 2011 at 10:09 PM, Snail Scott w=
=3D
rote:
> On Sep 13, 2011, at 11:58 AM, May Luk wrote:
>> ...New studio mate moved in and found her glaze crazed at the new set up=
=3D
;
>> same clay, same slip, same glaze. The most obvious difference from the
>> last set up is the kiln; a smaller size kiln...
>
>
> Might be quicker cooling, but might also not be the
> exact same level of vitrification. One kiln's sitter or
> controller is never equal to another's. Underfired clay
> can cause crazing even if the glaze looks matured to
> the same degree. Check the witness cones. If they are
> really giving the same reading, try =3DA0slowing the cooling
> in the lower range (below red heat); just =3DA0a tiny little bit.
> Or add some extra top and bottom insulation to the kiln.
> (Easier than doing the sides, and it still helps a lot.)
>
> =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =3DA0 =
=3DA0 =3DA0 =3DA0 =3DA0 -Snail
>
--=3D20
http://twitter.com/MayLuk
http://www.ceramicsbrooklyn.com/
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