Paul Borian on thu 19 apr 07
Does anyone know if small air bubbles trapped in a clay body could burst =
out during the glaze firing but not the bisque? I sometimes get these =
things that look like bubbles, usually only on thicker forms like large =
bowls and I have wondered if they are air pockets that release as the =
clay body matures. I soak for a long time, especially just below top =
temp, and the glazes do not look overfired when it happens and I know =
the clay body is not overfired as well because the test bars usually =
show 1%-2% absorption. In the last firing the only pots they showed up =
on were some large bowls as well as some smaller ones, and the bubbles =
were about =BC" in diameter with smooth edges and leaving the bare clay =
body exposed underneath. It kind of looks like there is a tiny hole in =
the clay body that is left exposed where something burst out and I am =
quite certain that it is not just something that the glazes are causing. =
Having several layers of glaze definitely has something to do with it =
but it does not seem to be just the glazes but instead something in the =
body.
So I wonder if it could be tiny air bubbles, but I tend to think they =
would be gone after the bisque. Or perhaps it is some other gas =
escaping?
Has anyone seen anything like this in their own work?
Thanks,
Paul
Dennis Newman on fri 20 apr 07
Paul, it sounds to me like you are glaze firing immediately after glazing. I
have had this problem if I don't wait 12-24 hrs after glazing before loading
and firing the kiln.
Quoting Paul Borian :
> Does anyone know if small air bubbles trapped in a clay body could burst out
> during the glaze firing but not the bisque? I sometimes get these things that
> look like bubbles, usually only on thicker forms like large bowls and I have
> wondered if they are air pockets that release as the clay body matures. I
> soak for a long time, especially just below top temp, and the glazes do not
> look overfired when it happens and I know the clay body is not overfired as
> well because the test bars usually show 1%-2% absorption. In the last firing
> the only pots they showed up on were some large bowls as well as some smaller
> ones, and the bubbles were about ¼" in diameter with smooth edges and leaving
> the bare clay body exposed underneath. It kind of looks like there is a tiny
> hole in the clay body that is left exposed where something burst out and I am
> quite certain that it is not just something that the glazes are causing.
> Having several layers of glaze definitely has something to do with it but it
> does not seem to be just the glazes but instead something in the body.
>
> So I wonder if it could be tiny air bubbles, but I tend to think they would
> be gone after the bisque. Or perhaps it is some other gas escaping?
>
> Has anyone seen anything like this in their own work?
>
> Thanks,
>
> Paul
>
>
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Ron Roy on wed 25 apr 07
Hi Paul,
Send this back with some more info.
What cone you firing at - ox or reduction? - how do you test for absortion
- what kind of clay - iron bearing?
When you break a bubble what does it look like inside?
It's not clear from this post how big the bubbles are and where they are.
RR
>Does anyone know if small air bubbles trapped in a clay body could burst
>out during the glaze firing but not the bisque? I sometimes get these
>things that look like bubbles, usually only on thicker forms like large
>bowls and I have wondered if they are air pockets that release as the clay
>body matures. I soak for a long time, especially just below top temp, and
>the glazes do not look overfired when it happens and I know the clay body
>is not overfired as well because the test bars usually show 1%-2%
>absorption. In the last firing the only pots they showed up on were some
>large bowls as well as some smaller ones, and the bubbles were about =BC" i=
n
>diameter with smooth edges and leaving the bare clay body exposed
>underneath. It kind of looks like there is a tiny hole in the clay body
>that is left exposed where something burst out and I am quite certain that
>it is not just something that the glazes are causing. Having several
>layers of glaze definitely has something to do with it but it does not
>seem to be just the glazes but instead something in the body.
>
>So I wonder if it could be tiny air bubbles, but I tend to think they
>would be gone after the bisque. Or perhaps it is some other gas escaping?
>
>Has anyone seen anything like this in their own work?
>
>Thanks,
>
>Paul
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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