Thank you very much for clearing that up for me.
LMac

On Mon, 28 Jul 2003 08:58:13 +1200, "annemarie"
wrote:


"Lindsay MacArthur" wrote in message
.. .
What type of structural damage can the crazing cause? Can this really
be caused by a 15-20 degree temp difference (the kiln was 92 F and the
outside temp was about 75-80 F when I unloaded)?
LMac

Crazing is not caused by a temperature drop it is caused because the clay
body and the glaze do no fit properly. It is not caused by unloading a warm
kiln. Remember this stuff should be oven proof.
For an example - The art society I belong to about 5 - 6 years ago was
having a lot of trouble with crazing, my goodness I sure heard the pinging
sound, it could go on for ages.
A lot of people there believed it was because of unloading a warm kiln and
tried letting the kiln cool to room temperature. This of course did no good
at all. They were mostly using a commercial clear glaze over underglaze
decoration. I thought it was more to do with the temperature they were
firing to and was lucky to attend a workshop run by a man called Royce
McGlashen a master potter and also supplier of clay.
The problem was we were firing too low for the clay we were using and it was
causing stress between the clay and the glaze which resulted in the crazing.
We lifted our firing temp and the problem dissapeared.
Crazing if it is extreame can cause a pot to break but usually just leaves
fine cracks in the glaze, which some people actually want for some things,
especially in raku firing and it is then called "crackle glaze" However
crazed ware is not food safe.
Good luck
Annemarie