SkyCeramic@aol.com on tue 25 feb 97
I am firing an electric kiln to cone 6, and have been having trouble with
certain glazes bubbling. It doesn't happen every time. And it never happened
in a different kiln. I tried soaking the kiln, which seemed to work once, but
the last time I had the bubbles again. (I don't have a pyrometer so am
guessing about the temperature). When the kiln went off I turned it back on
to 3 for 5 minutes and then Lo for 10 minutes.
All three problem glazes have copper in them.
Any suggestions about why this is happening?
Thanks so much,
Ruth Jacobson
The Shelfords on wed 26 feb 97
Ruth - What kind of copper? I find I have a lot of trouble with bubbling
with red copper, but less or none with black. The black copper is the more
commonly used colourant, but I had some red on hand, and used it to colour
clay. It makes a nice brown in the clay, green in or under glaze, but it
bubbles and fumes to the point of being not worth the trouble.
Veronica on Thetis
>----------------------------Original message----------------------------
>I am firing an electric kiln to cone 6, and have been having trouble with
>certain glazes bubbling. It doesn't happen every time. And it never happened
>in a different kiln. I tried soaking the kiln, which seemed to work once, but
>the last time I had the bubbles again. (I don't have a pyrometer so am
>guessing about the temperature). When the kiln went off I turned it back on
>to 3 for 5 minutes and then Lo for 10 minutes.
>All three problem glazes have copper in them.
>Any suggestions about why this is happening?
>Thanks so much,
>Ruth Jacobson
>
>
Marget and Peter Lippincott on wed 26 feb 97
SkyCeramic@aol.com wrote:
>
> ----------------------------Original message----------------------------
> I am firing an electric kiln to cone 6, and have been having trouble with
> certain glazes bubbling. It doesn't happen every time. And it never happened
> in a different kiln. I tried soaking the kiln, which seemed to work once, but
> the last time I had the bubbles again. (I don't have a pyrometer so am
> guessing about the temperature). When the kiln went off I turned it back on
> to 3 for 5 minutes and then Lo for 10 minutes.
> All three problem glazes have copper in them.
> Any suggestions about why this is happening?
> Thanks so much,
> Ruth Jacobson
Ruth:
I think that your soaking efforts are too timid. I assume you are on HI
when your kiln shuts off. Put it back on MED for at least an hour to
hold the top temp. Pyrometers are not very expensive and being able to
watch the temp would make me feel a lot more confident that I was doing
what I wanted to do.
I fire ^6 and have had bubble trouble with glazes containing rutile. Do
yours? Robin Hopper offered a more pure replacement for rutile
which may reduce the problem -- a mixture of RIO and titanium 1:2.
The last question is, if your claybody or glaze ingredients have changed
recently???
Peter
The Mudpuppy
Laura Vandenbogaardt on mon 12 nov 01
I used this blue glaze (Teal Blue) made by Western on 6 plates. I fired to
cone 05 and the glaze bubbled and pinholed. I applied the same glaze on them
(checked for pinholes from the glaze application this time and covered them
up) and refired to cone 05. They glaze bubbled again, this time worse. My
kiln is an old electric non-programable Skutt with a kiln sitter, timer and
two manual temperature dials. I didn't use the kiln sitter, I relied on
cones and a pyrometer.
I ran into some errors while firing though. I don't know if this is the
cause for the bubbling.
1) When I bisque fired to cone 05, I underfired them by about two cones.
The first glaze firing went good, it took 7 hours.
2) During the second glaze firing, the timer shut the kiln off when it
should have stayed on longer (another few hundred degrees to go). So the
kiln was off for 25 minutes and then I turned it back on to reach cone 05
temp. That firing took about 10 hours.
3) I used clear and black glazes on other pieces and they didn't bubble. Is
it the glaze I am using?
So I think the problem was the underfired bisque. If that is the problem,
can I rebisque some of the other pieces (I didn't glaze these and they are
from that original bisque) to the right temperature and then go ahead and
glaze them? Or is the problem the glaze? Or something else entirely? The
temp increase was steady and cooled steady.
I appreciate your help so much!
Ron Collins on mon 12 nov 01
I had similar problems, and decided to quit being so miserly, listen to
advice from clayart, and extend the firing. It seems to help to have the
time before red heat extend for a while. On the old kiln I was using that
was underpowered, I kept it on medium for maybe 3 hours......after that
time, there was still no color in the kiln. * I would like input on this
though: it is my understanding that the lower temps-before color in the
kiln -are the important times for a total burning off of
impurities......that once color begins, the clay more or less "seals itself"
and impurities are trapped within, and a longer bisque then will do no good.
Then you get bubbles and uglies......Is this factual? Melinda Collins,
Antigua, Guatemala
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