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bisque firing in a gas kiln-- still confused

updated thu 11 jul 02


Chuck and Tamara Schulz on wed 10 jul 02

Hi all,
Thank you so much to all of you who responded to my question.
Steve was right though, I didn't give enough information. I'm firing a
10cu.ft top-loading updraft kiln. The work is all less than 1/4" thick.
The load is packed relatively tight but is not tightly stacked--only a few
nesting bowls.
I had planned to do my first bisque firing today, but chickened out!
Decided to do more research first and now I'm REALLY confused!
I wanted to graph out a planned firing schedule, but can't seem to figure
one out. All of my books and the archives agree that bisque firing should be
"slow" or "very slow" but don't say what that actually means. How slow is
"slow"? Also, on some of the firing schedules I found, it wasn't clear
weather they included a candling period or if candling was done the night
before. So when you say that you fire to bisque in 4 hours, is that total
time or time after preheating?
Forgive me for being dense but this is just not sinking in!
Can anyone tell me, AFTER a period of preheating, what is a safe rate of
temperature increase?
And now, for the REALLY STUPID question. When I bisque in an electric kiln,
my schedule is (depending on thickness of ware) 1-2hrs. on low all peeps in
lid propped up 2". Then 1-2 hrs. on medium. Then, turn up to high, close lid
and wait 4-6hrs for kiln sitter to shut off. Can I use a schedule like this
with the gas kiln? If so, what temperature ranges am I dealing with in "low"
and "high"?
Thanks again,

Tamara --Okinawa

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Dan Dermer on wed 10 jul 02

How slow is slow? Here are the schedules I use in my Skutt electric kiln to
bisque to cone 05. Admittedly, this is easier to do in a programmable
electric kiln, but you could try for similar schedules in your gas kiln by
using a pyrometer and monitoring carefully. Climb rates in the critical
range from 1150 - 1650 degrees differ dramatically depending on whether I am
bisque firing red stoneware or white stoneware. From 1150 to 1650 degrees
Fahrenheit is the range for burning off organics in the clay.

For bisque loads with high iron content c10 stoneware, I have found that I
need to fire VERY slowly in order to burn out all the organics in my red
clay -- slower than I ever thought was necessary! Otherwise, I get black
coring and glaze shivering problems in subsquent reduction glaze firings.

These are the schedules I use -- your mileage may vary! Temperatures are in
degrees Fahrenheit...

For red c10 stoneware, with high iron content:
Climb Rate Temp Hold/Soak Time
100/hour 180 2-8 hours, depending on dryness of ware
250/hour 1000 (none)
100/hour 1150 (none)
75/hour 1650 (none)
150/hour 1910 (none)

For white stoneware (i.e. BMIX):
Climb Rate Temp Hold/Soak Time
100/hour 180 2-8 hours, depending on dryness of ware
250/hour 1000 (none)
100/hour 1150 (none)
150/hour 1650 (none)
180/hour 1910 (none)

Giving credit where credit is due -- thank you to all who have posted on
slowing down bisque firings! Once I finally heeded the advice, many
problems went away.