Dan Sommerfeld on fri 13 apr 07
I have been looking for a source listing casting times of Ball Clays.
Actually, I'd love to see numbers for feldspars and kaolins, too.
Does anyone know of a book/website with concise listings?
I am preparing a new casting slip and I'd like to try some different ball
clays. In some older posts clayarters have said to stay away from a
couple like OM-4, but finding a post that states some good ones have been
elusive. According to a company website OM-4 is desirable for casting,
but if you look at their literature almost all their ball clays say that.
Any help would be appreciated.
Thanks,
Dan Sommerfeld
karen gringhuis on sat 14 apr 07
Dan -
You may want to research formulas for casting slips
in general. I'm no expert on them but my
understanding is that plasticity is NOT what one wants
in a casting slip and that plasticity is once
characteristic of ball clays given their sm particle
size. Therefore I have to question why you want ball
clay in a casting slip - or at least how much of it in
a formula?
Cushing's Handbook incl some casting slip flormulas
you might want to compare to.
-------------
Dan wrote:
I have been looking for a source listing casting times
of Ball Clays......
.............. In some older posts clayarters have
said to stay away from a
couple like OM-4, but finding a post that states some
good ones have been
elusive
Karen Gringhuis
KG Pottery
Box 607 Alfred NY 14802
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Michael Wendt on mon 16 apr 07
Dan,
We cast with the same recipe
we use for the throwing body
made from Helmer Kaolin
which does the whole blush
pallet in wood fire. If there is
a supplier near you, you could
try our recipe:
Helmer Kaolin 50
Custer Feldspar 12.5
Nepheline Syenite 12.5
200 mesh Silica 25
This casts in our dry molds in
10-15 minutes and is plastic
enough to trim smoothly.
We screen the slip to 100 mesh
after it ages and periodically
during use to remove any lumps
so it stays smooth in the molds.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
USA
208-746-3724
http://www.wendtpottery.com
wendtpot@lewiston.com
Dan wrote:
I'm looking into ball clays for a body that I am
developing for a salt-
kiln. I have a white, translucent porcelain, but I
want a nice orange-peel
brown body for salt.
Dan Sommerfeld
Actually, I am trying to develop a good
Daniel Sommerfeld on tue 17 apr 07
Karen,
I have been casting and do sporadic research for a few years now, but I am
by no means an expert. Unfortunately most recipes are pretty generic like:
40 Kaolin
20 Ball Clay
20 Feldspar
20 Silica
Just like glazing, depending on which Kaolins, Feldspars, and Ball Clays
are used can cause huge differences in outcomes.
Once I substituted EPK for grolleg to see the difference in casting.
Grolleg had a 15 minute cast, but EPK took over 40 minutes.
Ball Clays do add plasticity to a cast. Sometimes it is desireable.
Every recipe I have used with ball clay trims better than an all Kaolin
repipe, and some all Kaolin recipes are almost impossible to trim.
Kohler's casting body for sanitary ware is 48% ball clay (4 varieties)due
to the processes required for building up their products.
I'm looking into ball clays for a body that I am developing for a salt-
kiln. I have a hite, translucent porcelain, but I want a nice orange-peel
brown body for salt.
Dan Sommerfeld
Actually, I am trying to develop a good
Daniel Sommerfeld on thu 19 apr 07
Michael,
(A warning: I go off on a tangent)
Thanks for the info. I have never tried Helmer, but it is on my short
list of Kaolins to try. My standard recipe is very similar using Grolleg
instead of Helmer. The grolleg imparts less titania and iron to the body
than Helmer; and the Alumina and Silica percentages are within one
percent. I have fired Grolleg, Tile 6, Kaopaque, EPK, Standard, and
Snocal bodies in an Anagama at the KIA and in salt. All the bodies had
similar blush and close color in the Anagama with the exception of the
Snocal (which is a very high Silica kaolin and reduces much more in the
kiln). In Salt the bodies show their differences in whiteness and
translucency with Tile 6 being the yellowest and Standard being the most
translucent. Grolleg and Standard contain more flux than the others so
adjustments could be made to equalize the recipes (ie. Grolleg recipe at
4% flux and Tile #6 recipe at 3% which sounds close until you realize that
their is a 33% difference between 3% and 4%).
Back to my search: These bodies don't contain enough alumina for the
effect I'm after in Salt, and the iron is too low. Your helmer and my
grolleg slipcast bodies break down like this:
Silica 64
Alumina 23-24
Flux 4
Iron .41 Grolleg - .69 Helmer
Titania .02 Grolleg - .57 Helmer
LOI 7 (around)
The body I'm trying to emulate is this:
Silica 50-55
Alumina 30-35
Flux 3-4
Iron 1.25-1.5
Titania no opinion (anyone: should I have one?)
LOI Balance
The feldspars and flint have good particle size for casting purposes, but
need to be limited to reduce the overall silica content. I may need to
leave silica completely out of the equation as clays alone have 40-55%
Silica. I may also need to use Alumina in place of the Silica, but that
gets expensive.
I ordered a bag of Tennesse #1 which is supposed to be a fast cast ball
clay. I will probably try velvacast for the kaolin. Add some redart for
color. Possibly some Goldart or find a coarse fireclay that may cast
fast. Maybe add some Molochite in place of the silica.
My goal is to get a bit closer on my first attempt by asking these
questions.
I'm open to ideas...
Thanks,
Dan Sommerfeld
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