[Clayart] Preheat

Jim Brown jbrown1000 at gmail.com
Wed Jul 20 10:53:12 EDT 2016


 "spoke to tech support today and he explained how to pre-heat. Actually
easy. I guess this is Key in bisque firing. Would this principle still
apply when glazing?" - Best, Ken

Once bisque, the possibility of blowing up is markedly reduced since it is
the moisture in the raw piece that is the big problem.  As the moisture is
heated above the boiling point of water, it turns to steam and, of course,
takes up much more space.  The result can be the explosion of the piece as
the steam can not find a way out fast enough.  With a slow heat and below
the boiling point, the moisture can find a way out.  The thicker a piece
is, the longer this period of slow heat must be and, of course, the clay
makes a big difference - "tight" clay will be more likely to blow than
clays with larger particulars.

After clay has been bisque, that moisture has left the piece and the
physical characteristics of the clay is also changed so most of the
problems with rapid heating are dissipated.  This depends, again, on the
clay being used.  The temps that most bisque to are normally considered
"earthenware" temps and most clays at this temp can be put on a stove or in
an oven and heated very quickly without a problem.   Although most can be,
pieces burned to "stoneware" temps may be more likely to present problems,
however.

So, short answer, if glazing on bisque the firing can go much faster.  I
do, however, still bring the temp of any burn up slowly until around 300
degrees.


*                       JIM BROWN*

*                 BROWN POTTERS*

*  "Making handmade pottery . . . *

*                                                . . . since the 1700's"  *
                   *   386 479-4515*
*            www.brownpotters.com <http://www.brownpotters.com>*
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