Judy Smith on tue 6 dec 11
I made a beautiful bowl with several different glazes that make a picture
with black outlines. I used a speckled clay with cone 6 oxidation Coyote
glazes. After I fired the bowl, I noticed that there are bubbles under
several of the glazes. These are large bubbles (1/4" to 1" in size). None
of the bubbles are ruptured. I had this happen once before with a black
clay and different glazes. The bubble on the black clay bowl was one large
4" bubble. I rinse all of my pottery and let them dry over night before I
glaze them. If I fire the bowl again, do you think the bubbles will
flatten out or will it just make it worse.
Thanks,
Judy Smith
William & Susan Schran User on tue 6 dec 11
On 12/6/11 9:03 AM, "Judy Smith" wrote:
> I made a beautiful bowl with several different glazes that make a picture
> with black outlines. I used a speckled clay with cone 6 oxidation Coyote
> glazes. After I fired the bowl, I noticed that there are bubbles under
> several of the glazes. These are large bubbles (1/4" to 1" in size). No=
ne
> of the bubbles are ruptured. I had this happen once before with a black
> clay and different glazes. The bubble on the black clay bowl was one lar=
ge
> 4" bubble. I rinse all of my pottery and let them dry over night before =
I
> glaze them. If I fire the bowl again, do you think the bubbles will
> flatten out or will it just make it worse.
You don't say what clay you are using or how high you are firing.
Do you fire with witness cones or Kilnsitter or program set in the kiln?
I would suspect the black clay may have been over fired if the bubble was i=
n
the clay, under the glaze. This is called boating caused by expansion of
gasses while the clay is still somewhat soft at high temperature.
If you are certain the same thing is happening with your speckled clay and
is not bubbles in the glaze, then check your firing with witness cones to
make certain you are not firing too high.
Refiring will make it worse.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Lee on wed 7 dec 11
Judy,
It may have nothing to do with the bisque (I have fired organic
black clays single fire.) But rather, the iron content of the clay and a
glaze over it that seals early. You didn't say what atmosphere you fired
in, only that you are using cone 6 oxidation glazes. Reduction, high
iron clay, and a early sealing glaze will often cause bloat.
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he land
of eternal youth is behind the house, a beautiful land fluent within
itself." -- John O'Donohue
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