Frederich, Tim on fri 3 jan 03
Hello and Happy New Year to everyone!
There has been a discussion on the end point of a cone and what the degree
difference would be. Orton states that the end point of a cone is the 90
degree bending angle, also referred to as the 6 o'clock position. This
point would be when the tip of the cone is even with the top of the cone
plaque or the line in the base of a self supporting cone. If the tip of the
cone touches the shelf it is slightly overfired. This will not be a problem
in most cases because it might only be a couple of degrees F in actual
temperature. As stated by others you should make your decisions based upon
the results of how your ware looks and the position of the cones at that
particular point. Each cone has a certain number of degrees in temperature
from when it begins to deform until it reaches the 90 degree angle. If for
example the degree spread for a cone is 35 degrees F from start to finish,
the number of degrees from the 1 o'clock to the 4 o'clock positions might be
27 degrees with the remaining 8 degrees being from the 4 o'clock to 6
o'clock position. A cone will fall faster toward the end of its deformation
because of increasing melt of the materials and the effect of gravity on the
cone.
There also has been discussion on firing schedules. I agree with the
opinions of John Hesselberth and fire faster during the early stages of the
firing and slow down toward the end to allow for more even absorption of
heat throughout the ware and the kiln. I also slow down for Quartz
inversion (573 C- 1063 F). There are many opinions on how slow or fast to
fire a kiln and it again comes down to deciding what works for you and the
ware that you are making. My opinion is that slower firing is usually
better than a fast firing.
I think that the end result of this discussion should be to look, listen and
pay attention to what your work, the cones and your observations are telling
you. A kiln, either manual or computerized, is a wonderful tool but you
should always monitor each firing and not depend on the kiln to do
everything for you.
Have a great 2003!
Best regards,
Tim Frederich
Orton Ceramic Foundation
6991 Old 3C Highway
Westerville, OH 43082
Phone: 614-895-2663 x 36
Fax: 614-895-5610
E-mail: frederich@ortonceramic.com
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