tony clennell on tue 8 jan 08
Teri: Sounds like ya got lots to think about in your quest for the
ghost of carbon trap. We have made our living exclusively from this
glaze for the past 5 or 6 years. (200+ firings) I guess you would say
we have it nailed but that said some firings are a 7 out of 10 and
others closer to 10 out of 10. As Liz said it can be how the stars
lined up that night more often I have found a good rainy overcast day
to be a blessing.
It is has been years since we had the dreaded walrus snot green. I
agree with others this has to do with very heavy application of glaze
and too much smoking early in the firing. Remember smoke is the enemy
of reduction.
Here are some of my superstitions about using this glaze
1. the glaze must be made at least 24 hours before using it and we put
it through our Talisman screen each time before using it for the day.
this helps get the thickness more even. Thickness has a HUGE impact on
the look of CT glazes.
2. we glaze everything that day, load and candle overnight
3. reduction begins at 012 just beginning to tip
4. reduction with a climb in temperature ( the oxyprobe is just over
6) a higher reading than 7 is creating smoke but i think is
interfering with reduction.
5. we climb to Cone 9 in medium reduction again at around Oxyprobe
6- 6.5 and slow the kiln down at Cone9 for an hour soak till 10 is
down. We use a red clay slip that needs to be soaked or it bubbles up
thru the shino.
At another time in our life we made our living from another maverick
glaze- Rutile Blue. To help me sleep at night we bought a Oxyprobe.
this is the best insurance on the market for a studio potter counting
on the kiln load to pay some bills while the others wait. Even though
everything we do on the kiln is like clockwork now I do like to look
at the probe reading and feel some confidence that there isn't
something trying to ruin my day.
All the best and welcome to the Black Side.
Tony
--
http://sourcherrypottery.com
http://smokieclennell.blogspot.com
Bruce Girrell on tue 8 jan 08
Tony Clennell wrote:
> 3. reduction begins at 012 just beginning to tip
> 4. reduction with a climb in temperature ( the oxyprobe is just over
> 6) a higher reading than 7 is creating smoke but i think is
> interfering with reduction.
Tony, just how do you manage to get that sort of reading on the Oxyprobe at
such a low temperature?
Bruce Girrell
tony clennell on tue 8 jan 08
Bruce:
Good point! the temperature is 1632 F when 012 is usually tipping and
the oxyprobe reads just 5.5- 6 The probe is the crown of the arch so
that is probably the hottest part of the kiln at that time. Any temp
lower than that and i see what you're saying- can't get a reading.
dunno it works here!!! Usually in the first 15 minutes it fluctuates
but with the damper going in and the gas being turned up the kiln
jumps usually 100 degrees in a half hour and the probe settles down.
Best,
Tony
On Jan 8, 2008 12:51 PM, Bruce Girrell wrote:
> Tony Clennell wrote:
> > 3. reduction begins at 012 just beginning to tip
> > 4. reduction with a climb in temperature ( the oxyprobe is just over
> > 6) a higher reading than 7 is creating smoke but i think is
> > interfering with reduction.
>
> Tony, just how do you manage to get that sort of reading on the Oxyprobe at
> such a low temperature?
>
> Bruce Girrell
>
> ______________________________________________________________________________
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--
http://sourcherrypottery.com
http://smokieclennell.blogspot.com
Rod on tue 8 jan 08
Bruce,
The zirconium pellet at the end of your probe will react to atmosphere at
1200F i.e red heat. If your probe is not reacting at this temp then the
pellet may be exhausted (rare) or a wire on your probe is defective which
sometimes can work at higher temperatures.
The zirconium pellet on the probe is no different than that of a catalytic
converter. Which is why when you first start your car it may run rough for a
few minutes until the element that heats the zirconium gets it's job done
and brings the pellet to reactive temperature.
All oxy-probes regardless of the manufacturer will become less and less
accurate after 50-60 firings at cone 9-10. If you remove the probe at high
temperature - before adding soda or salting you will cut the life of that in
half again.
What took me seven years to learn from firing shino glazes is that I
personally have had much more consistent results now that I buy my soda ash
1-2 years in advance. In other words after it has been sitting around bagged
in the studio for a year or so I get consistent results every firing, but if
I start using a new bag straight from the supplier then chances are I'll
open the kiln after 3 great firings and then WHAM I'm back in green snot
hell - anyone that fires kiln loads of shino knows this is not a nice place
to be.
Shino is defiantly a much more touchy beast on bodies high in nepheline
syenite eg., porcelain and some white stoneware. I never had a problem
firing shino on stoneware, I must be very lucky as I never saw a snot green
shino until I switched to porcelain.
Cheers,
Rod
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of tony clennell
Sent: Tuesday, January 08, 2008 1:03 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: The Ghost of Carbon Past
Bruce:
Good point! the temperature is 1632 F when 012 is usually tipping and
the oxyprobe reads just 5.5- 6 The probe is the crown of the arch so
that is probably the hottest part of the kiln at that time. Any temp
lower than that and i see what you're saying- can't get a reading.
dunno it works here!!! Usually in the first 15 minutes it fluctuates
but with the damper going in and the gas being turned up the kiln
jumps usually 100 degrees in a half hour and the probe settles down.
Best,
Tony
On Jan 8, 2008 12:51 PM, Bruce Girrell wrote:
> Tony Clennell wrote:
> > 3. reduction begins at 012 just beginning to tip
> > 4. reduction with a climb in temperature ( the oxyprobe is just over
> > 6) a higher reading than 7 is creating smoke but i think is
> > interfering with reduction.
>
> Tony, just how do you manage to get that sort of reading on the Oxyprobe
at
> such a low temperature?
>
> Bruce Girrell
>
>
____________________________________________________________________________
__
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots2@visi.com
>
--
http://sourcherrypottery.com
http://smokieclennell.blogspot.com
____________________________________________________________________________
__
Clayart members may send postings to: clayart@lsv.ceramics.org
You may look at the archives for the list, post messages, or change your
subscription settings here: http://www.acers.org/cic/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots2@visi.com
Lee Love on wed 9 jan 08
Tony, Rod,
I think the carbon trap glazes are not the same as the
spodumene shinos. Do you both use 17% soda ash?
--
Lee in Mashiko, Japan
http://groups.google.com/group/ClayCraft
"Men are born ignorant, not stupid. They are made stupid by
education." -- Bertrand Russell
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