iandol on thu 31 jan 02
Dear Sarah House,
The three examples given by Tim Fredrich are just that, examples which =
show some general principles. One of these is that there is nothing =
happening in the clay heating can be rapid. The second is that if =
something is about to occur then it must be a slow temperature rise. The =
third is that the reactions which bring both clay and glaze to maturity =
happen over a fairly long time span.
If these factors are read in conjunction with the notes of say, Daniel =
Rhodes or Frank and Janet Hamer then a clearer picture will reveal =
itself.
For example. Although a hold time is recommended at 185=B0F a =
considerable amount of steam is released during the run up to about =
1300=B0F. If the work in the kiln is that of novices or students and the =
clay is both thick and or varying cross section 360=B0F rise per hour =
may be excessive.
For example. In green clay the particles are loosely held. It is not a =
rigid structure. So the particles of quartz, if there are any, are =
small. If they fracture because of the quartz inversion the effect will =
be almost unnoticeable. It is doubtful if the fissures would connect =
across the other components to give a full blown "Dunt"
I think Tim Fredrich missed a golden chance. He has, in effect given us =
just one program in his article. He could have given us two programs, =
one for Going Up, and one for Going Down. Having said that, please read =
his note on "Points to Remember". this is good advice.
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