craig clark on mon 19 mar 01
I've read on the list and have known for a number of years that pots =
that aren't bone dry can be successfully bisque fired. This is something =
that I've not yet attempted but would like to do in the next coupla =
days. I'm planning on throwing a number of sacrificial lambs this =
evening. If they don't make, no great loss.
The question that I have is how is this done? I understand the =
principle but am unaware of the specific technique involved. For =
instance; at what point do I place the pots in the kiln? Do they need to =
be freshly thrown, or is it best to let them get toward a leather hard =
state (for obvious reasons.) Do I fire as if it is a "normal" bisque =
full of bone dry pots?
Any help, or explanations will be greatly appreciated!
Thanx
Craig Dunn Clark
Houston, Texas (where this bloody winter is hangin on way the hell to =
long! It's gonna be in the upper 40's again this evening. This just =
isn't acceptable! If I wanted to freeze my kister off I'd move to =
Mina-freezin-sootta.)
Rod, Marian, and Holly Morris on tue 20 mar 01
I wet fire a lot because I teach short term kids classes in the summer and
always have to rush. It's terrible for the (electric) kiln, by the way.
Thickness is really the issue, from my experience. Once I fired a very dense
load of leather hard work, ramped at 280 an hour, no pre-heat. No problems
because it was all thin slab work (using a sculpture clay, by the way, or
I'm sure I would have had cracking) with very little variation in thickness.
The class was "Make a Clay Dish Set", and I turned around a dish set,
glazed, for 15 kids in one week. On the other hand, I have had a pot not
just crack, but pretty much blow up at 300, even after the 12+ hours at 180
I gave the load. I'm pretty sure the issue was a thick bottom. Nowhere for
the steam to go.
My usual modus is to load the kiln after the day in class, wet, leather,
whatever, then set the kiln to 180 or 190 and leave it for at least 12
hours, sometimes more if there is a lot of stuff. By all means, leave the
top cracked at least 2." Otherwise the steam has nowhere to go and is even
worse on your elements than it already is.
This method does not work for tiles, however. Those I put between two layers
of wallboard or ceiling tile, and they need around 24 hours at 180-190
before they are dry. I often do this in my oven, where the air circulation
is good. I can't get past warping when I fire wet tiles.
I was very intrigued by a recent thread on "damp drying." For us cowgirls
who force dry and fast fire, this was a very interesting exchange, and I
plan to try the methods this summer with my kids classes.
Marian in Michigan
----- Original Message -----
From: "Jim and Marge Wade"
To:
Sent: Tuesday, March 20, 2001 6:47 PM
Subject: Re: Method for bisque firing green ware?
> Do you think a hold for 3 hours at 180 F in a bisque firing is enough for
> leather hard pots to be sure the moisture is out of them? I fired a bisque
> load of some student's work this way recently and one bowl broke
completely
> in half. The top peep hole of the kiln was left open, but the lid was not
> propped. Although this bowl was drier than leather hard, it did have a
> thicker bottom. I've never had a pot crack before and don't want it to
> happen again. Should I be holding longer? I reviewed this ramp program
with
> Skutt before firing it the first time, so I feel the ramping is probably
> O.K. and that my problem is that I didn't hold it long enough. One clay
> center I know of holds for 12 hours at 180 F. That seems like a long time.
>
> Any suggestions?
>
> Marge Wade
>
>
>
> > From: Martin Howard
> > Reply-To: Ceramic Arts Discussion List
> > Date: Tue, 20 Mar 2001 06:40:01 -0000
> > To: CLAYART@LSV.CERAMICS.ORG
> > Subject: Method for bisque firing green ware?
> >
> > Craig Dunn Clark
> > There is no real problem firing leather hard greenware. IMHO.
> > So long as the ramp is set low until the water is driven off and the top
> > vent is open during that time, they fire quite happily.
> > I change the ramp each hour or so during the first 500 degrees C. Then
its
> > on full power.
> > The pots go in when I am ready. The earliest finished might be getting
on
> > towards bone hard. Those that have just been finished to complete orders
or
> > deadlines will still be leather hard, or just slipped or just glazed (at
> > leather hard). I have not tried putting in wet pots, because I always
want
> > to turn and slip or/and glaze, all at leather. The pots go in and out of
> > leather stage until they go into the kiln.
> > One that has dried too much goes in for a bisque fire (that means it is
> > placed at the bottom of the kiln rather than higher up). Most childrens'
> > work and some students work is bisqued.
> > So, don't fear pots having some water in them. Just use common sense
about
> > ramping and ventilation (but don't needlessly waste electricity).
> >
> > Martin Howard
> > Webb's Cottage Pottery
> > Woolpits Road, Great Saling
> > BRAINTREE, Essex CM7 5DZ
> > England
> >
> > martin@webbscottage.co.uk
> > http://www.webbscottage.co.uk
> >
> >
____________________________________________________________________________
__
> > 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.
>
>
____________________________________________________________________________
__
> 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.
>
Martin Howard on tue 20 mar 01
Craig Dunn Clark
There is no real problem firing leather hard greenware. IMHO.
So long as the ramp is set low until the water is driven off and the top
vent is open during that time, they fire quite happily.
I change the ramp each hour or so during the first 500 degrees C. Then its
on full power.
The pots go in when I am ready. The earliest finished might be getting on
towards bone hard. Those that have just been finished to complete orders or
deadlines will still be leather hard, or just slipped or just glazed (at
leather hard). I have not tried putting in wet pots, because I always want
to turn and slip or/and glaze, all at leather. The pots go in and out of
leather stage until they go into the kiln.
One that has dried too much goes in for a bisque fire (that means it is
placed at the bottom of the kiln rather than higher up). Most childrens'
work and some students work is bisqued.
So, don't fear pots having some water in them. Just use common sense about
ramping and ventilation (but don't needlessly waste electricity).
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Mike Gordon on tue 20 mar 01
Craig,
I've never tried to fire freshly thrown pots, how do you trim them? I do
fire very wet trimmed pots. So wet that they deform when picked up. I
put the kiln on piolt over night, gets to around 350-375 by 7:30 the
next AM. I think problem arise when there are air bubbles in the walls
or they are too thick. I fire as usual. Get to about 750 around 11 AM
and 1200 by 1PM then full blast till temp C04 usually around 3PM, Mike
Jim and Marge Wade on tue 20 mar 01
Do you think a hold for 3 hours at 180 F in a bisque firing is enough for
leather hard pots to be sure the moisture is out of them? I fired a bisque
load of some student's work this way recently and one bowl broke completely
in half. The top peep hole of the kiln was left open, but the lid was not
propped. Although this bowl was drier than leather hard, it did have a
thicker bottom. I've never had a pot crack before and don't want it to
happen again. Should I be holding longer? I reviewed this ramp program with
Skutt before firing it the first time, so I feel the ramping is probably
O.K. and that my problem is that I didn't hold it long enough. One clay
center I know of holds for 12 hours at 180 F. That seems like a long time.
Any suggestions?
Marge Wade
> From: Martin Howard
> Reply-To: Ceramic Arts Discussion List
> Date: Tue, 20 Mar 2001 06:40:01 -0000
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Method for bisque firing green ware?
>
> Craig Dunn Clark
> There is no real problem firing leather hard greenware. IMHO.
> So long as the ramp is set low until the water is driven off and the top
> vent is open during that time, they fire quite happily.
> I change the ramp each hour or so during the first 500 degrees C. Then its
> on full power.
> The pots go in when I am ready. The earliest finished might be getting on
> towards bone hard. Those that have just been finished to complete orders or
> deadlines will still be leather hard, or just slipped or just glazed (at
> leather hard). I have not tried putting in wet pots, because I always want
> to turn and slip or/and glaze, all at leather. The pots go in and out of
> leather stage until they go into the kiln.
> One that has dried too much goes in for a bisque fire (that means it is
> placed at the bottom of the kiln rather than higher up). Most childrens'
> work and some students work is bisqued.
> So, don't fear pots having some water in them. Just use common sense about
> ramping and ventilation (but don't needlessly waste electricity).
>
> Martin Howard
> Webb's Cottage Pottery
> Woolpits Road, Great Saling
> BRAINTREE, Essex CM7 5DZ
> England
>
> martin@webbscottage.co.uk
> http://www.webbscottage.co.uk
>
> ______________________________________________________________________________
> 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.
mary ann on wed 21 mar 01
I'm assuming you're firing in an electric kiln. With two peepholes open I can hold
a mirror to the top one and watch it steam up from the escaping moisture. When it
quits doing that I crank up the kiln. Really thick pots need special attention. I
had one the other day I took into the house and baked in the oven at 200 degrees
(F) for not along enough because it still crumble exploded but I could have dried
it out and also gone slower with the bisque firing.
Mary Ann in Ithaca
Jim and Marge Wade wrote:
> Do you think a hold for 3 hours at 180 F in a bisque firing is enough for
> leather hard pots to be sure the moisture is out of them? I fired a bisque
> load of some student's work this way recently and one bowl broke completely
> in half. The top peep hole of the kiln was left open, but the lid was not
> propped. Although this bowl was drier than leather hard, it did have a
> thicker bottom. I've never had a pot crack before and don't want it to
> happen again. Should I be holding longer? I reviewed this ramp program with
> Skutt before firing it the first time, so I feel the ramping is probably
> O.K. and that my problem is that I didn't hold it long enough. One clay
> center I know of holds for 12 hours at 180 F. That seems like a long time.
>
> Any suggestions?
>
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