Dave Finkelnburg on wed 19 jan 00
Kiln gurus,
Ginny's successful bisque firing--great work, by the way!--raises a
question in my mind. I, too, have encountered rapid temperature rise
immediately at the start of a gas firing. My burners have a lot of
turndown, though and I can manage just fine. I am wondering, though, how
slow you really do need to go between candling to really bone dry (less than
200 degrees F) and say 400 to 500 degrees. At what point do you start
kicking off chemically bound water that could ruin the ware? Is there a
gap between drying the greenware and driving off bound water where the ware,
being somewhat open and porous, can handle rapid heating early in the
firing?
Right now I am following a very careful 150 degree F/hour temperature
increase from candling to 1,600 F for greenware firing. I am just
wondering if I can safely speed up this process in some areas. It seems
like it would save time and fuel!
Thanks for considering this question.
Dave Finkelnburg pondering why there's no snow, it's 45 degrees F,
and raining in January Idaho
dfinkeln@cyberhighway.net
Cindy Strnad on wed 19 jan 00
Dave,
It's my understanding that chemically bound water will have dissipated by
the time the kiln reaches around 500 degrees F. If I'm mistaken, I would, of
course, appreciate being corrected. That said, I fire at 150 degrees an hour
(after a hold time at 180 degrees F. to safely get rid of non-bound water)
until I reach 500 F., then go all out.
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Mark & Pauline Donaldson-Drzazga on thu 20 jan 00
----- Original Message -----
From: Cindy Strnad
To:
Sent: 19 January 2000 22:40
Subject: Re: kiln report--firing speed question
> ----------------------------Original message----------------------------
> Dave,
>
> It's my understanding that chemically bound water will have dissipated by
> the time the kiln reaches around 500 degrees F. If I'm mistaken, I would,
of
> course, appreciate being corrected. That said, I fire at 150 degrees an
hour
> (after a hold time at 180 degrees F. to safely get rid of non-bound water)
> until I reach 500 F., then go all out.
>
> Cindy Strnad
> Earthen Vessels Pottery
> Custer, SD
>
Dear Clayarters,
forget about whether its the right temperature (500F) or not. What are the
parameters? Is the clay very thick? is it a raw glaze firing? etc. etc. All
firings and kilns and potters temperaments are different. So the firing
cycle is a massive variable. I fire my thick and large pieces (gas, 2
burners downdraught 1.3cu.m., raw glazes and terracottas)) over a period of
27 hrs with the fastest time after 900C up till 1170C, then a soak for 40
minutes and off.
Happy potting Marek http://www.moley.uk.com
martin howard on thu 20 jan 00
In "Ceramic Faults and their Remedies" by Harry Fraser, on page 10 we can
read:-
Around 450-500C chemically bound water begins to dissociate from the clay
mineral. By 650C most of the chemically bound water has been driven off but
the bond is quite tenacious and some traces of water vapour will continue to
be produced up to 900 C and beyond. (this is partly due to temperature
gradients which may be 100C or more in thick wares.)
So, Cindy, you might be assuming the water has gone rather too soon.
Martin Howard
Webb's Cottage Pottery
Woolpits Road
Great Saling
BRAINTREE
Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
www.webbscottage.co.uk Should be ready for 2000 :-) or 2001
Ron Roy on thu 20 jan 00
Hi Cindy,
Holding below boiling till no more water vapor is the way I do it -
everyone seems to disagree between what range the chemically bound H20 is
released. Holding something at a spy hole on which the water will condence
(I use a piece of shiny stainless) will tell you when it starts and stops -
say every 30 min.
I've seen water well after 500C.
I don't think anything blows up when the chemically bound is being released
- better to slow down from 700C to 900C to make sure all the carbon and
sulphur etc. gets out and the iron stays oxidized.
R
>----------------------------Original message----------------------------
>Dave,
>
>It's my understanding that chemically bound water will have dissipated by
>the time the kiln reaches around 500 degrees F. If I'm mistaken, I would, of
>course, appreciate being corrected. That said, I fire at 150 degrees an hour
>(after a hold time at 180 degrees F. to safely get rid of non-bound water)
>until I reach 500 F., then go all out.
>
>Cindy Strnad
>Earthen Vessels Pottery
>Custer, SD
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Frederich, Tim on thu 20 jan 00
Cindy,
It is my understanding that chemically bound water does not start to
release until about 800 degrees F and possibly finishes around 1300 degrees
F. This water is released very slowly and does not usually pose any danger
of exploding. Hope this info helps.
Sincerely,
Tim Frederich, Orton Ceramic Foundation
> ----------
> From: Cindy Strnad[SMTP:earthenv@gwtc.net]
> Sent: Wednesday, January 19, 2000 5:40 PM
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: kiln report--firing speed question
>
> ----------------------------Original message----------------------------
> Dave,
>
> It's my understanding that chemically bound water will have dissipated by
> the time the kiln reaches around 500 degrees F. If I'm mistaken, I would,
> of
> course, appreciate being corrected. That said, I fire at 150 degrees an
> hour
> (after a hold time at 180 degrees F. to safely get rid of non-bound water)
> until I reach 500 F., then go all out.
>
> Cindy Strnad
> Earthen Vessels Pottery
> Custer, SD
>
Jeremy/Bonnie Hellman on fri 21 jan 00
I've exploded pots in the bisque kiln at anywhere from 400 degrees F to
almost 900 degrees F. This occurred with pots where the walls (usually the
base) were thicker than I thought and (apparently) not completely dry. Now I
dry on a raised surface so air can circulate all around my pots. Also with
larger pots, I (try to remember to) check EVERY side to see that it's dry.
Bonnie
Bonnie Hellman in Pittsburgh, PA
> From: Ron Roy
> Reply-To: Ceramic Arts Discussion List
> Date: Thu, 20 Jan 2000 18:32:14 EST
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: kiln report--firing speed question
>
> ----------------------------Original message----------------------------
> Hi Cindy,
>
> Holding below boiling till no more water vapor is the way I do it -
> everyone seems to disagree between what range the chemically bound H20 is
> released. Holding something at a spy hole on which the water will condence
> (I use a piece of shiny stainless) will tell you when it starts and stops -
> say every 30 min.
>
> I've seen water well after 500C.
>
> I don't think anything blows up when the chemically bound is being released
> - better to slow down from 700C to 900C to make sure all the carbon and
> sulphur etc. gets out and the iron stays oxidized.
>
>
>
> R
>
>> ----------------------------Original message----------------------------
>> Dave,
>>
>> It's my understanding that chemically bound water will have dissipated by
>> the time the kiln reaches around 500 degrees F. If I'm mistaken, I would, of
>> course, appreciate being corrected. That said, I fire at 150 degrees an hour
>> (after a hold time at 180 degrees F. to safely get rid of non-bound water)
>> until I reach 500 F., then go all out.
>>
>> Cindy Strnad
>> Earthen Vessels Pottery
>> Custer, SD
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough
> Ontario, Canada
> M1G 3N8
> Evenings 416-439-2621
> Fax 416-438-7849
ferenc jakab on fri 21 jan 00
Ron, if you're firing a gas kiln you will see water vapour coming at over
600 Deg c even because the gas gives off water vapour during combustion.
Feri.
NakedClay@aol.com on sun 23 jan 00
In a message dated 1/21/00 10:01:51 AM Pacific Standard Time, Bonnie writes:
> ---------------------------Original message----------------------------
> I've exploded pots in the bisque kiln at anywhere from 400 degrees F to
> almost 900 degrees F. This occurred with pots where the walls (usually the
> base) were thicker than I thought and (apparently) not completely dry. Now
I
> dry on a raised surface so air can circulate all around my pots. Also with
> larger pots, I (try to remember to) check EVERY side to see that it's dry.
>
> Bonnie
=============================
Hi Bonnie and others on this thread!
I concur with Bonnie--I made this gaffe (firing pots I thought were
plenty dry, but blew up during bisque), and began to revisit my definition of
"bone dry" after the third "explosion."
I know a potter who "candles" the fully-loaded bisque kiln for about an
hour, before turning the heat on "low." This is done to further dry out the
bone-dry pots, and assures that the wares will not explode, once the bisque
fire approaches its "cone down" state.
Milton NakedClay@AOL.COM
Dry and cool in the Mojave Desert.
Frederich, Tim on tue 25 jan 00
Alisa,
The cone should be placed in the pack so that the the number is
facing you and the rough edge or spine of the cone is opposite the side that
will bend over. The number side should not be on the face that will be
bending. If you have other questions, please ask.
Sincerely,
Tim Frederich, Orton Ceramic Foundation
> ----------
> From: Alisa and Claus Clausen[SMTP:aliskin@mail.dk]
> Sent: Monday, January 24, 2000 2:42 PM
> To: CLAYART@LSV.UKY.EDU
> Subject: Sv: Re: kiln report--firing speed question
>
> ----------------------------Original message----------------------------
> ------------------
> Hi Tim,
> Blah, I just bought orton cones and can not find the following info. in my
> catalog.
> I forgot how to place them in the kiln pack.
>
> Which way should the pressed in cone number face? For example, I have
> three
> cones in the pack all tilting a bit forward, and the cone mark it facing
> forward. Is this correct. I do not want them to melt doing backdives!
>
> Thank you
> Alisa in Denmark
>
Gail Dapogny on thu 27 jan 00
Dear Alisa,
In case you ever get confused or forget what Tim from Orton told you, you
can stand (with a little help!) the cone on its flat end, and see which way
it wants to fall. That's the plane that should face forward, and 99%
percent of the time it will put the number facing you, just as Tim said.
Every once in a while it is abnormal and so I always test it by seeing how
it wants to fall.
--Gail
>> Which way should the pressed in cone number face? For example, I have
>> three
>> cones in the pack all tilting a bit forward, and the cone mark it facing
>> forward. Is this correct. I do not want them to melt doing backdives!
>>
>> Thank you
>> Alisa in Denmark
>>
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
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