iandol on thu 13 mar 03
Dear Bill Edwards,
Thank you for your impassioned response.
If you were to search back throughout the archives, no not Clayart =
shelves, but the work of the real pioneers who started to exploit the =
other physical properties of Porcelain, or highly vitrified clay bodies, =
you might find they were working with their "True Porcelains" between =
cone 16 and cone 20.
In one sense, discussions about firing ranges for porcelain or any other =
clays are moot. This is important since it gets us back to real ideas of =
what happens in our kilns. We know once liquid phase sintering starts, =
provided we keep heat going into the kiln the process will continue to =
completion. The rate of reaction is temperature dependent. We have =
choices; of rapid heating to high temperature in a short time, or a =
lower heat input over a long time period. The effective input of Energy =
(Joules per Kilogram per hour) could be achieved by holding at 1150=B0 C =
for several hours or even days, or by heating directly to 1300=B0. Yet =
you could say both were Cone 10 firings if that was what the cone pads =
told you.
I suppose in the end it comes back to acceptable conventions. Do we call =
a flat sheet of steel on the end of a wooden pole a spade of a shovel?
Best regards,
Ivor
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