klauzer jessica a on tue 20 oct 98
Hello anyone willing to adress my concern:
I just unloaded my last cone 10 salt firing from the salt kiln here at CU
in Boulder Colorado. It is a great kiln and I have fired it 9 or 10 times
so far with no real problems. I usually do a 10 minute oxidation period
at the end after salting to get rid of the atmosphere (simply because
someone told me to so that the glazes don't bubble or something like
that), and I had always been successful in doing this. But this time,
after a particularly heavy salting, the oxidation period did not clear out
the kiln. I wanted to shut it down because it was getting too hot (cone
11 bending a little bit), so after 15 minutes I decided to shut it off.
But there was still smoky vapor (white) coming out of the stack by the end
of it. When I closed the damper, the vapor started seeping out of the
door and peeps. Could the salt on the inside of the kiln still be
volatilizing at this heat? My kiln mate suggested that we open the damper
to let it out, and she proceeded to do so. I could only stand it for five
minutes, worrying that the kiln was cooling off too quickly like that (the
color had gotten significantly dimmer in that time) and I closed it back
up. Two days later, when we were unloading, a few pieces that I had in
there seemed to have thin cracks through the clay body that had been fused
with glaze. Could this quick cool-off have caused something like this?
The pots had a fake ash glaze with high barium inside with bare clay on
the outside. Also, what would this residual salt atmosphere do to the
pots and do I even need to bother with the oxidation period? The glazes
were all pretty nice with no bubbling or anything monstrous like that.
Thanks so much for enduring my long-winded explanation and thanks in
advance for any advice or wisdom about salt fumes you might be able to
provide.
jessica
in colorado -- having our first frost :(
Donn Buchfinck on wed 21 oct 98
In my personal experience of salt glazing
the kiln soaks in salt and starts to release it
if you do a heavy salting 15 minutes might not be enough to clear it out
and if you salt heavy and do not clear it out, one might get a rough surface
and I find a slow cooling at the high temeperatures helps the growth of some
wonderfull things in salt glazes.
I look at the amount of salt I want to introduce to the kiln and start around
c 8 putting it in
then I make sure it is done around c 10 with about 30 minutes to clear the
salt
salt reduces the kiln, and I find I like reduced porcelain salted.
so in the end even if you think you have cleared out the salt, the kiln itself
will continue to release the salt.
and I wouldn't fast cool because cooling slow is when we get our wonderfull
colors, that is why a pull ring looks dull but the finished pots look great.
Donn Buchfinck
Ray Carlton on thu 22 oct 98
hi jessica .... i hope you are not using that high barium liner glaze for
fuctional stuff like bowls that people will eat out of...barium is a highly
toxic substance...your other bits i can't really comment on with
authority..however i feel that your 15 minute quick cool would not cause
cracks..cracks will occur at dull red heat but the glaze will not fuse over
them [dunting] it is more likely that the pots cracked during
drying...sometimes pots develop hairline cracks not really obvious till
after firing...
good luck
At 12:15 20/10/98 EDT, you wrote:
>----------------------------Original message----------------------------
>Hello anyone willing to adress my concern:
>
>I just unloaded my last cone 10 salt firing from the salt kiln here at CU
>in Boulder Colorado. It is a great kiln and I have fired it 9 or 10 times
>so far with no real problems. I usually do a 10 minute oxidation period
>at the end after salting to get rid of the atmosphere (simply because
>someone told me to so that the glazes don't bubble or something like
>that), and I had always been successful in doing this. But this time,
>after a particularly heavy salting, the oxidation period did not clear out
>the kiln. I wanted to shut it down because it was getting too hot (cone
>11 bending a little bit), so after 15 minutes I decided to shut it off.
>But there was still smoky vapor (white) coming out of the stack by the end
>of it. When I closed the damper, the vapor started seeping out of the
>door and peeps. Could the salt on the inside of the kiln still be
>volatilizing at this heat? My kiln mate suggested that we open the damper
>to let it out, and she proceeded to do so. I could only stand it for five
>minutes, worrying that the kiln was cooling off too quickly like that (the
>color had gotten significantly dimmer in that time) and I closed it back
>up. Two days later, when we were unloading, a few pieces that I had in
>there seemed to have thin cracks through the clay body that had been fused
>with glaze. Could this quick cool-off have caused something like this?
>The pots had a fake ash glaze with high barium inside with bare clay on
>the outside. Also, what would this residual salt atmosphere do to the
>pots and do I even need to bother with the oxidation period? The glazes
>were all pretty nice with no bubbling or anything monstrous like that.
>Thanks so much for enduring my long-winded explanation and thanks in
>advance for any advice or wisdom about salt fumes you might be able to
>provide.
>
>jessica
>in colorado -- having our first frost :(
>
cheers Ray Carlton
McMahons Creek Victoria Australia
paul on fri 23 oct 98
Jessica,
Just a couple of things. 1) If the cracks were glazed over, that means that
the cracks developed before the glazes melted, if it was a sharp crack in
the clay and glaze then it happen in the cooling. 2) salt can vaporize at
a rather low temp - it is possible to salt red earthenware - they key is
that the clay must be vitreous to allow for the soda to bond with the silica
and alumina. 3) If these are functional be careful of high barium glazes in
the interior, OK! 4) I usually quick cool my pots for 1/2 hour to keep
the body a little lighter in color - this still allows for nice blushes and
very warm tones - not anything like what the draw tiles look like. This
helps to keep the glazes brighter from clearing out all of the extraneous
gases.
good luck - Paul Wilmoth
-you wrote:
*When closed the damper, the vapor started seeping out of the
door and peeps. Could the salt on the inside of the kiln still be
volatilizing at this heat?
*I could only stand it for five
minutes, worrying that the kiln was cooling off too quickly like that (the
color had gotten significantly dimmer in that time) and I closed it back
up. Two days later, when we were unloading, a few pieces that I had in
there seemed to have thin cracks through the clay body that had been fused
with glaze.
*The pots had a fake ash glaze with high barium inside with bare clay on
the outside.
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