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kiln shelf deterioration

updated sun 31 aug 97

 

Susan Goldstein on sun 3 aug 97

I recently bought replacement shelves from ART for my old Olympic kiln. When
I fired my cone 6 runny glazes they dripped on the shelves as usual.
However, when I chiselled them off substantial pieces of the shelf crumbled
out with the glaze. This has not happened before. On several shelves I had
a good coating of Lee's Kiln Wash and on others I had my traditional mix of
Silica and EPK. There was absolutely no difference between the two. Can
someone tell me what is going on?

Susan

Talbott on mon 4 aug 97

Susan...
Sounds like the kiln wash has worn thin or was not applied to a
sufficient thickness to give adequate protection.. We usually apply two or
three coats of kiln wash on the shelves... Also sounds like the shelves
are of a high alumina composition and are relatively soft... We use
nitride bonded SiC shelves that are very hard.. I use a 6" body grinder
with a wire cup brush to clean off glaze drips and I only use a chisel and
hammer at a 30 degree angle or less to knock off stubborn drip areas...
(Make sure to wear eye safety goggles and a dust mask) This occurs when I
fail to recoat my shelves with kiln wash over a long period of time after
repeated firings.. If your glaze is really runny then place a "clay foot"
of bisqued clay beneath the pots to catch the drips...(like a coaster)
The Lee's is a necessity for us because we fire cone 9/10 reduction and we
cannnot afford to have flakes of kiln wash ruining our pottery.. one tiny
flake of kiln wash in a platter during a glaze fire and there goes a
$75-$100 loss in sales. For us there is NO question or debate as to which
kiln wash to use. LEE'S is the way. ... Marshall

>----------------------------Original message----------------------------
>I recently bought replacement shelves from ART for my old Olympic kiln. When
>I fired my cone 6 runny glazes they dripped on the shelves as usual.
> However, when I chiselled them off substantial pieces of the shelf crumbled
>out with the glaze. This has not happened before. On several shelves I had
>a good coating of Lee's Kiln Wash and on others I had my traditional mix of
>Silica and EPK. There was absolutely no difference between the two. Can
>someone tell me what is going on?
>
>Susan

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