Snail Scott on fri 21 mar 03
At 08:00 PM 3/20/03 -0500, you wrote:
>This time someone
>put the electric kiln on high
>--pretty full of some glaze tests--
>thought they put it on lo...
>Do you guys think these glaze tests were
>compromised?
No. Going directly to 'hi' on a regular basis can
be a strain on the elements, but the main reason
we start with 'lo' is to ease greenware gently
past the dangerous steam-producing (and exploding-
clay-producing) temperatures. I assume your tests
were on bisque, but even if they weren't, they
apparently didn't go 'boom'!
The speed of a glaze firing is mainly relevant in
the later stages approaching vitrification, and
the speed of firing through the low temperatures
has no real effect on glazes.
So, your firing may have hit temperature an hour or
so early, but since the rate of increase was only
altered during the early hours, your glaze tests
should still be as accurate as ever.
-Snail
karen gringhuis on sun 23 mar 03
Speed of firing affecting glaze tests -
Scott is probably right about speed of firing up
having negligible effect. But if your tests were of
mat glazes, I know from personal experience that the
speed of cooling definitely affects the surface. Fast
cooling can push a mat glaze into a semi glossy
surface. For this reason, and because I favor slow
firing up to develop the glaze, I am leary of tests
fired in very small test kilns. I would trust them
more for hue than for surface.
In any case, a test is still a test - a first reading
as it were. (I have some tests I've never been able to
replicate!) Before going to lift-off, I would first
fire further tests of slightly larger batches in a
typical kiln firing.
=====
Karen Gringhuis
KG Pottery
Box 607 Alfred NY 14802
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