Lili Krakowski on tue 28 feb 06
Justin's disaster brought out the troops. Thank goodness.
But permit me to repeat, stress, emphasize one point.
When Hermann Seger, of blessed memory, invented cones, he started with c.1.
Which today, in the Orton cone series, represents 2077/2109 degrees
F--depending on rate of heating.
For reasons I do not know Seger later decided to have cones for lower temps.
And worked BACKWARD, AS IN NEGATIVE NUMBERS.
So he created c.01 which today, in the Orton series is 2043/2079 F depending
on rate of heating.
N.B that the 01 heated at 270 degrees per hour in the last 90-120 minutes of
firing--or so the chart in the Bailey Catalog reads--achieved 2 degrees more
than the c.1 fired at 108 degrees. In other words mighty close.
Well, the cones prefaced by a zero move way down....and those not preface by
a zero move way up.
And so, if, as some intuited, Justin may have used/punched in a 6 instead of
an 06 (6=2228/2266; 06 = 1823/1852) she would have overfired her ware by a
whole whole lot.
A girl can't be too careful, as the saying goes.
So read your cones carefully. Realize that the junior cones that go in the
kiln sitters, and the Pyro Bars (also for sitter) and the self-supporting
cones, and the regular large or standard cones are NOT identical. And that
you need to test, and experiment a bit, and check what works in your kiln,
with your style of firing.
In my kilns I need a pyro bar one number higher, even two than my witness
cone. It is not a hard and fast rule, density of stacking, of shelves does
affect results...but whatever you do, read you cones, read the charts...and
if you have something you program, be careful.
Also realize that if you are using older cones--and I have some I have had a
long time, because I do not fire to that temp often--the temp of recently
made cones has been revised. So that what once was a c.Whatever glaze may
demand a little less, a little more heat than then.
In my considered opinion, if in doubt, underfire.
Lili Krakowski
Be of good courage
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