Anthony Allison on thu 8 jun 00
Dear Mark,
when a speedy firing is needed, we have found that if you are careful at
certain temperatures, you can raise the temps very rapidly.
The critical points are 439 degrees F and 1060 degrees F. You must use a
probe and an accurate digital pyrometer. Even with the probe you need to =
use
a bit of thoughfulness. For example, perhaps your kiln is hotter where t=
he
probe is and cooler elsewhere. Or cooler at the bottom and hotter at top.
Large platters or large pots are probably not candidates for fast fire. =
We
always creep up slow up to 439 degrees and 500 degrees. Then the burners =
can
be throttled open wide. Slow down at 1000 degrees and soak upward to 12=
00
degrees. Then you can really open "er up.
My large kiln, with eight burners at the fastest can fire to cone 10 in
about eight hours. My smaller kiln makes it to 10 in about 4 hours.
Wishing you luck. If you miss the slowdowns, you will see cracks due to t=
he
induced stresses.
Tony
-----Original Message-----
From: Mark Brown
To: CLAYART@LSV.CERAMICS.ORG
Date: Thursday, June 08, 2000 4:41 PM
Subject: Firing- Rate of Temperature?
>What is the fastest rate I should increase the temperature of a gas
>kiln for bisque and also for cone 10 glaze firing?
>
>First of all, this is a loaded question. I know there are many
>varibles that have to be considered and even then the answer could be
>five pages long. I know the slower the better. But how fast is safe
>enough? Let's say the givens are the ware is medium thickness and
>size, average functional ware, packed not too tight, ware is
>completely dry in a 9 cu. ft. propane kiln.
>
>I have been firing at a rate of 150=B7F/ hour and everything is
>fine. I
>know I can fire faster than this but I'm not sure how much faster.
>I should move slow from 900=B7F to 1300=B7F, right, how slow? Any
>help would be appreciated.
>
>Thank you, Mark B.
>
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Mark Brown on thu 8 jun 00
What is the fastest rate I should increase the temperature of a gas
kiln for bisque and also for cone 10 glaze firing?
First of all, this is a loaded question. I know there are many
varibles that have to be considered and even then the answer could be
five pages long. I know the slower the better. But how fast is safe
enough? Let's say the givens are the ware is medium thickness and
size, average functional ware, packed not too tight, ware is
completely dry in a 9 cu. ft. propane kiln.
I have been firing at a rate of 150=B7F/ hour and everything is
fine. I
know I can fire faster than this but I'm not sure how much faster.
I should move slow from 900=B7F to 1300=B7F, right, how slow? Any
help would be appreciated.
Thank you, Mark B.
Nikom Chimnok on fri 9 jun 00
At 15:33 8/6/00 +0000, Mark Brown wrote:
>What is the fastest rate I should increase the temperature of a gas
>kiln for bisque and also for cone 10 glaze firing?
***********************************************
No one can answer this question. There are too many variables, the biggest
one of which is: What kind of clay? And smaller: How wet is this dry clay?
Which will depend on your local relative humidity.
You can learn the answer to your question by risking pots. Fire them faster
and see what happens. The 3 dangers of too-fast firing are explosion,
cracking, and black coring. If one or more of those happens you know you are
going too fast, and better luck next time.
You can design a clay to fire fast: Load it up with things like grog, talc,
wollastonite, kyanite and even kaolin. The ingredients you can't fire fast
are ball clay, bentonite or red clay--stuff with small particle size where
water won't migrate quickly, and which has a high water of plasticity to
begin with.
Our local red clay has been fired (not very successfully) for 24 hours for
the last 300 years. But modified as suggested above I can fire the same clay
with virtually no breakage in 6 hours.
Nikom in Thailand
Paul Taylor on sat 10 jun 00
Dear Mark
You are right it depends on the clay . I have a fire clay here that has so
much coal (carbon) in it that one degree centigrade a minute was too much
for it in a gas kiln. I had to soak at 800c for two hours. I sometimes
wonder if I set fire to it it may fire its self. I made planters out of it
to get it out of the workshop. I originally bought it to add to my clay to
make it more oven proof.
The clay I use normally is cheap stuff dug in stoke, it still has plenty
of carbon in it so I dare not go more than 100 (212F) degrees centigrade per
hour after watersmoke and well oxidized for an hour at 800c (1472f).
I reckon if you are getting a good oxidized biscuit at 65 degrees
centigrade(150f) per hour you are winning. You could go to the 100c per hour
for unlided thin stuff (212f). Would the savings you make in gas Justify you
pushing it too far and losing a kiln load to bloating - or the worry.
To stoneware I go as quickly as possible to 1000 c then reduction to 1260
at one degree centigrade per min to cone 8-9, knowing that I am safe to do
so. If I get bloating it is because I stack pots too near the flame but I
need a few seconds to encourage people to my studio.
If I am firing my porcelain the firing is very complicated in my attempts
to get a right Celedon.
Regards Paul Taylor
> From: Mark Brown
> Reply-To: Ceramic Arts Discussion List
> Date: Thu, 8 Jun 2000 15:33:12 +0000
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Firing- Rate of Temperature?
>
> What is the fastest rate I should increase the temperature of a gas
> kiln for bisque and also for cone 10 glaze firing?
> _________
Ron Roy on mon 19 jun 00
Hi Mark,
One of the most important considerations is how much iron and
carbon/sulphur there is in the clay. Fire clay usually has some course iron
(specking) and that can be a problem if the iron is reduced during the
bisque.
200 F per hour (for a cone 10 firing would not be too fast. So much depends
on how you like your glazes - if you reduce firing time there will be some
glazes that may not be as likable - this can be compensated for by
increasing the flux or reducing the refractories to make them melt more -
but the body interaction with the glaze will be affected.
If your clay body is developing a significant amount of cristobalite a slow
firing from 1100C on is not the best idea.
When you change firing speed after 1600F you can have an affect on fit.
Yes - it is a short answer but I see many others have spoken up - I just
thought to bring up the fit change thing - let me know if you need more in
that area.
RR
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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