Jeremy McLeod on thu 9 may 02
Mine is a "Olde Tech" studio with a rebuilt Skutt 818 and kilnsitter.
I've been bisquing to a ^06 taking six or so hours to do so.
3-4 hours on Low, 2 hours on Medium, remainder on High.
It's been an attempt to save some electricity costs by being on
the lower settings longer.
This has proven inadequate in the matter of getting gasses
out of the clay body. Recently several of my pieces have
enough pinholes to suggest a memorial to Lawrence Welk
and the Bubble Machine. :-(
So, given my Olde Tech resources, what would y'all suggest
as a better firing regimine. I'm hoping that someone on the
list either has good long-term memory (from waaayyyy back
then when they didn't have a computerized kiln) or current
experience with solving this problem.
Thanks
Jeremy McLeod
Dave Gayman on thu 9 may 02
Some things jump to mind.
First, make sure your pinholes are not the result of dust / loose particles
on the surface of the bisque as it's being glazed.
Try bisquing to ^04 (hotter, more organics burn out, but more costly in
energy). I'm working only with commercial clays these days, but all of
them recommend ^04 for bisque.
Read your meter with a variety of firing methods. Taking a long time at
low might eat MORE electricity...
Check your glaze materials -- have you recently bought any new ones, with
possibly more stuff to burn out during maturing?
Check your glaze fluidity -- tougher with rough (under fired) glazes, but
mattes and glossies should flow enough to heal pinholes.
Check your last hour(s) of glaze firing -- should be slow to allow
relatively slow boiling and enough time for healing.
If all else fails, go the other direction (see crater-glazed pottery by
Gertrude & Otto Natzler, example at
http://www.fmhs.cnyric.org/community/everson/syrchina/Natzler.html)
At 09:30 AM 5/9/2002 -0600, you wrote:
>bisquing to a ^06
>
>n inadequate in the matter of getting gasses
>out of the clay body.
>pinholes
Craig Martell on thu 9 may 02
Hi:
You probably need more heat work at hi temp to remove volatiles. You could
hold 06 for a couple of hours and see if this helps or you could raise your
temp to 04. I don't know what your claybody is but some clays really need
a long hold at hi temp to get all the crud out. Don't worry about saving
electricity, it's not that much more $$. Your time and your work are what
you want to save.
I've never used a computer controlled electric.
regards, Craig Martell in Oregon
Jeff Lawrence on thu 9 may 02
Jeremy was describing his pinholing after a 6-hour bisque to 06.
Hi Jeremy,
I suffered this problem for a long time, absolutely convinced
that a bisque was a bisque, no matter how fast I got there, and
tinkering with the glaze recipe to fix the problem.
Eventually, I found that an 8 or 9 hour bisque eliminated the
pinholes. As I recall, I'd do low for 2 hours, medium for 6 hours
and high for something less than an hour until the sitter dropped.
Sometimes (due to phase of the moon? less dense load?) the sitter
would drop at about the 8 hour mark just with medium settings.
Best regards,
Jeff
Connie Waring on thu 9 may 02
> hold 06 for a couple of hours and see if this helps or you could
Please excuse this beginner question, but I've always wondered about
this....
From what I read, cone 06 is not exactly equivalent to a specific
temperature - it's measuring "heat work" which is a combo of
temp + time
When someone says (or you read) hold at a certain cone, I'm confused.
Once cone 06 bends completely, even if you kept the kiln at the same
exactly temperature, aren't you really going to an equivalent higher
cone because of the time factor?
I'm not sure I'm asking my question correctly,
hopefully someone can translate and explain it.
thanks so much, I've always wondered about this,
connie
Paul Taylor on mon 13 may 02
Dear Connie
Good point. I think the statement comes with our attachment to cones as a
better indicator of glaze maturity
Holding at cone something is nonsense but we all know what the potter
means. At top temperature we all indulge in a soak trying to keep the
temperature at the hottest part of the kiln constant while we hope other
parts of the kiln that have not reached that temperature catch up. Yes the
hooter part of the kiln the glaze is fluxing more but it a matter of
relativity you are judging that the pots will take a little less heat
relative to the ones in the cold spot.
Usually the extra half hour or so will not drop the cone more because
when we turn the kiln down the flame gets shorter or the draft changes or
something (Kiln firing is still a back art). so the other parts of the kiln
benefit from the change and heat up to the required temperature.
Heat work does make a different because the cones are always a little
down after you open the kiln due to the cooling even when you cool quite
quickly.
The trouble with firing is that it is not a precise thing - using the
equipment we can afford. To much of an extent precision is unnecessary
because a good glaze should look the same over a range of two or more cones.
But good glazes are a bit boring. Potters want crystals and runny bits so
ironically the people who for artistic reasons need the precision can not
afford it .
As well There are two schools of thought involved. There are the
potters who fire as an art form, in strange sounding oriental kilns who try
to control the effects of what some would see as disaster. And the people
like me who need to control every part of the firing for the impression we
want to give. every thing is ok till we start talking to each other.
The confusions are only apparent when you think about them too deeply.
firing kilns is an art, you fire and fail and fire again until you get the
feel of what is going on and you record as much as possible, the weather
your mood, the temperature , atmosphere pressure, secondary air setting the
amount of flame showing in a crack in the brick work - no measurement is too
fine.
And when you tell every body how you did it, you just say what to a
clear thinker is nonsense, "I held the kiln at cone eight" -- and every body
knows what you mean.
--
Regards from Paul Taylor
http://www.anu.ie/westportpottery
" You might be a potter if someone talking 'jibberish' is making perfect
sense to you".
> From: Connie Waring
> Reply-To: Ceramic Arts Discussion List
> Date: Thu, 9 May 2002 17:32:41 -0700
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: How Slow is Slowwwww?
>
>> hold 06 for a couple of hours and see if this helps or you could
>
> Please excuse this beginner question, but I've always wondered about
> this....
>
> From what I read, cone 06 is not exactly equivalent to a specific
> temperature - it's measuring "heat work" which is a combo of
> temp + time
>
> When someone says (or you read) hold at a certain cone, I'm confused.
> Once cone 06 bends completely, even if you kept the kiln at the same
> exactly temperature, aren't you really going to an equivalent higher
> cone because of the time factor?
>
> I'm not sure I'm asking my question correctly,
> hopefully someone can translate and explain it.
>
> thanks so much, I've always wondered about this,
>
> connie
Snail Scott on wed 15 may 02
At 05:32 PM 5/9/02 -0700, you wrote:
>Once cone 06 bends completely, even if you kept the kiln at the same
>exactly temperature, aren't you really going to an equivalent higher
>cone because of the time factor?
If ^06 bends completely, then you're at a 'cone o-six
bent completely' heatwork level, which is higher than
'cone o-six bent to 9:00', etc. If a cone keeps
bending, then the heatwork is increasing, even if the
actual temperature of the kiln is not rising.
-Snail
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