Paul B on tue 3 may 05
I fire to cone 11 and sometimes get these bubbles on the finished pots when
i use certain combinations of glazes or when the glazes are applied too
thick, like with copper reds. Even after a 1/2 soak at cone 10/11 it does
not change things, and the strange thing is that often the bubble leaves
bare clay underneath, which makes me wonder what temp this is happening. I
would think if it happened at top temp, the glaze would flow back over the
spot, like if it was due to outgassing or something like that; but if it is
happening further on in the cooling process that would account for why it
comes out like this. If i could figure it out i could soak at a lower temp
and see what it does.
Any info on this?
thanks,
Paul
Bruce Girrell on tue 3 may 05
Paul,
Lately I have been playing with draw rings. My particular interest is
looking at the formation of iron, pyroxene, and rutile crystals during
cooling, but draw rings would also be a useful tool for determining when
your bubbles are forming.
Bruce "If you want more information, just give me a ring" Girrell
marianne kuiper milks on wed 4 may 05
I had the same problem with a raku piece: the
off-white opaque glaze (from class studio, exact
substances unknown to me) was covered with little and
large craters. It is possible that the fire was not
hot enough for this glaze. For a problem like this you
may want to add some frit to bring the needed temp.
for the glaze to mature down, enough to prevent the
bubbles/craters.
--- Stephen Powell wrote:
> I experienced the same small circles of bare clay on
> some of my pots that I
> had double dipped and fired in reduction to cone 10
> half way down. One of
> the glazes was a high iron with manganese and cobalt
> and the other contained
> cobalt and manganese. The problem only occurred on a
> body high in iron and
> even then not on all of them. I have previously
> fired the same combination
> without problem. the only other factor I can think
> of was that the items
> were fairly thinly potted which would have affected
> the take-up of glaze on
> the surface. Any ideas would be much appreciated.
> Steve P.
> ----- Original Message -----
> From: "Paul B"
> To:
> Sent: Tuesday, May 03, 2005 5:35 AM
> Subject: WHAT TEMP DO GLAZE BLISTERS/BUBBLES FORM?
>
>
> >I fire to cone 11 and sometimes get these bubbles
> on the finished pots when
> > i use certain combinations of glazes or when the
> glazes are applied too
> > thick, like with copper reds. Even after a 1/2
> soak at cone 10/11 it does
> > not change things, and the strange thing is that
> often the bubble leaves
> > bare clay underneath, which makes me wonder what
> temp this is happening. I
> > would think if it happened at top temp, the glaze
> would flow back over the
> > spot, like if it was due to outgassing or
> something like that; but if it
> > is
> > happening further on in the cooling process that
> would account for why it
> > comes out like this. If i could figure it out i
> could soak at a lower temp
> > and see what it does.
> > Any info on this?
> > thanks,
> > Paul
> >
> >
>
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> >
>
>
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Judy Rohrbaugh on wed 4 may 05
I have a glaze that took a bit of work to get right. It is fired to cone 6,
a plum brown with blue running through it. The higher it is fired, the more
blue. It contains cobalt and a small amount of iron ox.
When I fire it over a clay body that contains some manganese, it does
similar things to what you are talking about. It's no good.
When I fire it over a white clay body, it never turns blue, just a dull
brown. And when I use it over a clay that contains a bit of iron, it works, and
can look great.
Maybe a different clay body would give better results?
Judy Rohrbaugh
Fine Art Stoneware
_fineartstoneware@aol.com_ (mailto:fineartstoneware@aol.com)
Ohio
Jim Willett on thu 5 may 05
While I am not sure what you are describing is the same thing we have
experienced, we had similar problems, especially with a double dipped
glaze for a long time. There seemed to be no rhyme or reason to it. Some
pieces had glaze crawls leaving bare clay and some did not. What we have
determined in our case to be the problem (we think!) is that the moisture
in the glaze vaporizes when the initial ramp past 212 degrees happens too
quickly. If the glaze is completely dry (meaning in our case 24 hours at
least from application to firing) the ramp can be fairly quick. If the
wear is glazed and then loaded and fired sooner than that we slow our
initial ramping by a period of hours, holding the temperature of the ware
below boiling for sometimes as long as 9 hours. There seems to be strength
to our argument because we have eliminated the problem and no longer see
any bare clay where we don't want to see it. Our process is different of
course as we are electric fired cone 6 but we have a colleague who fires
cone 10 gas who reported similar problems and a similar remedy. Hope this
helps.
Jim Willett
Out of the Fire Studio
Edmonton, Alberta, Canada
http://www.outofthefirestudio.com
Stephen Powell on thu 5 may 05
Thanks for your response.
The glazing had taken place some weeks before firing and there was no
obvious blistering before firing. The strange thing is that some pots were
ok and some looked as if they had the measles!
----- Original Message -----
From: "Jim Willett"
To:
Sent: Thursday, May 05, 2005 6:38 AM
Subject: Re: WHAT TEMP DO GLAZE BLISTERS/BUBBLES FORM?
> While I am not sure what you are describing is the same thing we have
> experienced, we had similar problems, especially with a double dipped
> glaze for a long time. There seemed to be no rhyme or reason to it. Some
> pieces had glaze crawls leaving bare clay and some did not. What we have
> determined in our case to be the problem (we think!) is that the moisture
> in the glaze vaporizes when the initial ramp past 212 degrees happens too
> quickly. If the glaze is completely dry (meaning in our case 24 hours at
> least from application to firing) the ramp can be fairly quick. If the
> wear is glazed and then loaded and fired sooner than that we slow our
> initial ramping by a period of hours, holding the temperature of the ware
> below boiling for sometimes as long as 9 hours. There seems to be strength
> to our argument because we have eliminated the problem and no longer see
> any bare clay where we don't want to see it. Our process is different of
> course as we are electric fired cone 6 but we have a colleague who fires
> cone 10 gas who reported similar problems and a similar remedy. Hope this
> helps.
>
> Jim Willett
> Out of the Fire Studio
> Edmonton, Alberta, Canada
> http://www.outofthefirestudio.com
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Stephen Powell on thu 5 may 05
I experienced the same small circles of bare clay on some of my pots that I
had double dipped and fired in reduction to cone 10 half way down. One of
the glazes was a high iron with manganese and cobalt and the other contained
cobalt and manganese. The problem only occurred on a body high in iron and
even then not on all of them. I have previously fired the same combination
without problem. the only other factor I can think of was that the items
were fairly thinly potted which would have affected the take-up of glaze on
the surface. Any ideas would be much appreciated.
Steve P.
----- Original Message -----
From: "Paul B"
To:
Sent: Tuesday, May 03, 2005 5:35 AM
Subject: WHAT TEMP DO GLAZE BLISTERS/BUBBLES FORM?
>I fire to cone 11 and sometimes get these bubbles on the finished pots when
> i use certain combinations of glazes or when the glazes are applied too
> thick, like with copper reds. Even after a 1/2 soak at cone 10/11 it does
> not change things, and the strange thing is that often the bubble leaves
> bare clay underneath, which makes me wonder what temp this is happening. I
> would think if it happened at top temp, the glaze would flow back over the
> spot, like if it was due to outgassing or something like that; but if it
> is
> happening further on in the cooling process that would account for why it
> comes out like this. If i could figure it out i could soak at a lower temp
> and see what it does.
> Any info on this?
> thanks,
> Paul
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Jim Willett on fri 6 may 05
We have one other thought on this and then we are out of suggestions. If
some of your ware was improperly bisqued, impurities in the clay which
normally would have burned out in the bisque still have to burn out of the
clay, only now they go through the glaze. Too cool a temperature or the
lack of a proper soak at the end of the bisque firing will sometimes leave
impurities behind. After that we have no more guesses!
Jim
http://www.outofthefirestudio.com
http://www.howtomakepottery.com
Ron Roy on sat 7 may 05
Hi Judy,
Watch out for Manganese - in clay or glazes - the dust is a real health
hazard as are the fumes from firing it.
RR
>I have a glaze that took a bit of work to get right. It is fired to cone 6,
>a plum brown with blue running through it. The higher it is fired, the more
>blue. It contains cobalt and a small amount of iron ox.
>When I fire it over a clay body that contains some manganese, it does
>similar things to what you are talking about. It's no good.
>When I fire it over a white clay body, it never turns blue, just a dull
>brown. And when I use it over a clay that contains a bit of iron, it works, and
>can look great.
>Maybe a different clay body would give better results?
>
>Judy Rohrbaugh
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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