Lee Love on thu 14 oct 04
David Hendley wrote:
>
>I had gotten cheap and lazy.
>After decades of bisque firing, I thought I knew what cone 06
>looked like, so I stopped using a cone and fired according to
>time and atmosphere color.
>
>
Yee-haw! A craftsman can tell the temperature by the color
in the kiln. ;-) Fukiyan was retired Foreman I worked with, 78 years
old, started with Hamada at the age of 14. He ONLY judged the
temperature in a noborigama bisque by the color in the chamber. The
largest osara (the $30,000.00 ones) and the large tsubo were bisqued for
noborigama glaze firing in the gas kiln, but everything else for the
noborigama was bisqued to red heat in the noborigama. The gas kiln
bisque was done by apprentices to temperature according to an analog
pyrometer. But the hottest part in the large gas kiln was only up to
cone 012.
In Japan, they bisque at a lower temp. I believe it is
industry that got us bisquing at higher temps. Glaze thickness
application is very important to my teacher's work. The lower
bisque, I am guessing, gives him more control over the thickness of the
glaze.
>Gradually, the temperature dropped. Hey, what's wrong with
>saving a few bucks worth of electricity?
>
>All went fine until I started making some large bowls (16"
>diameter and greater). More than half cracked. Cooling cracks
>which ran up the side from foot to rim.
>
>
Lower bisque is softer, so it isn't for the clumsy or lazy, but
people learn to work with it here in Japan.
As I said previously, the hot part of my woodkiln bisques to
012. The bottom front is cooler, but not as cool as the coldest spots
in the noborigama bisque.
>see, there really is a pretty great difference in the strength of ware
>fired at C 08 vs. C06 - at least with my claybody. The stronger
>clay can take the phase changes on the way down, but the
>flimsy soft bisque cannot.
>
>
I've never had these kinds of cracks in my lower
temperature bisque and I never saw them at my teacher's studio either.
I have been bisquing to 012 since '91. . Could it be a fault of
the clay you are using? Does it have a high silica content?
Difference between cone 06 and cone 06.5 isn't going to
make a noticeable difference in energy usage. But the difference
between cone 06 and 012 can be measured on you meter.
--
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