Kat Valenzuela on mon 9 dec 02
Bruce
There is a great difference in ball clays. I test them by calcining half
and mixing with
regular. Fire to several different temperature including cone 10red. OM#4
has to be
the dirtiest of all ball clays. (most inconsistent) Spinks blend I have
found quite clean.
Yet if you are firing at such a low temperature I am not sure if it will
matter to much.
(especially in oxidation) Using EPK would be best.
Grolleg is quite white (translucent) and costly, mixing it with ball clay
makes no sense. A Kaolin gets
its translucency by having a very low titanium content. (that is why
Grollege is so popular)
EPK is very white, (not translucent)
with some plasticity, Grolleg has extremely low plasticity.
Talc will help with burnishing and to keep a low thermal expansion. (it
will also act as a flux)
Petalite has no thermal expansion and would help with thermal shock. The
more you can
get into the body the better it is. Yes you can use spodumene in place of
Petalite but it needs to
be replaced by using 75% spodumene with 25% feldspar. Petalite bodies are
excellent for oven ware.
The down side is that most glazes will craze on a petalite body due to it's
very low expansion. Then again you are firing quite low anyhow, you may
not be adding glaze since you are burnish the body.
Your clay body recipe looks good, as long as you find the physical quality
are what you need it to be.
Maturity doesn't seem to be an issue since you are firing so low.
Hope this helps
Kat in the Hat
kat@digitalfire.com
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