[Clayart] Preheat

Ken Chase kchase235 at gmail.com
Wed Jul 20 13:10:16 EDT 2016

Thanks again Jim:
Just reviewed my notes and concede the bisque firing was of too short a duration.
Just removed reglaze pieces which look good.
Fired at medium with no hold time.
The one I had to discard was an experiment that failed. I used a craze mat glaze over sprayed with gloss clear. Won't be doing that again.

Sent from my iPad

> On Jul 20, 2016, at 7:53 AM, Jim Brown <jbrown1000 at gmail.com> wrote:
> "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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