Alan Wainright on wed 3 jul 96
Dear Valerie:
On Monday, 1 July, you wrote:
> I have been using a white clay from Great Lakes Clay, covering
> with Duncan Cover Coat & firing to 04. When they are clear-
> glazed & fired to 06, they all craze. What am I doing wrong?
I passed your question along to Christy Runyan, one of our clay
gurus, and here's her reply:
"The lowfire process requires accurate firing to eliminate crazed
ware. Are you using 'witness' cones? These are the true firing
record of your kiln. As stated on the Duncan labels, your firing
must be to _witness_ cone 06, which usually means you need to use
one cone hotter (ie, 05) in your kiln sitter.
"Depending on the clay, I usually bisque fire to 03 or even
hotter to 02, which makes the ware more durable, and glaze fire
to a cone 05."
One more question: which of Duncan's lowfire clears are you
using? The leaded ones (GL611 & GL612) are more resistant to
crazing, but shouldn't be used on functional pieces that will
have contact with food or drink. The leadfree clear, IN1001, can
be real finicky about firing to the right temperature (as
Christy's note above).
I hope this helps: good luck!
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