David Clark on sun 18 mar 07
Hi all,
I am searching for opinions on the following.
I have mixed and tested a cone 1 soft stoneware casting slip. It's nice and
strong but it shrinks a little too much and warps a bit too much. It's from
Chappell's book pg.56 of the revised ed. recipe SSC-2:
Kaolin 30
Neph. Syen. 26
Kentucky ball #4 20
Silica 11
Talc 13
He suggests sodium carb at .3 but I like darvan
The thing is, he does not specify a kaolin as he does in other recipes so I
used Imerys because it's white. I had used it before in some porcelain that
I was playing with previously. From What I can gather this is not the best
grained kaolin to use in a casting recipe but..this is what I used.
In bisque it shrank 6.3% and 8.5 to cone 1. warping occurred more than
desired but could be due to not fully dried green ware. It's very humid
here now with the snow and the nature of my shop. I fired slow bisque on my
computer controlled elec kiln.
since I will be casting large objects I am concerted with the warping. the
recipe according to Chappell is supposed to shrink 6.6% when fired to Cone
4. Since I have everything specific to his recipe except his kaolin choice
I assume it is the Imerys that is causing my undesired effects.
Glazes work very nice. super smooth.
I have thought that I could adjust the ball content and remove some kaolin
by about 5%, maybe add a touch more silica but the ball increase should
cover this. I believe.
But, maybe theres a better Kaolin choice that will bring me closer to
Chappells results?
Thanks much for any comments
David
Beacon, NY
845-440-3533
Lynn Goodman Porcelain Pottery on mon 19 mar 07
On Mar 18, 2007, at 1:09 PM, David Clark wrote:
>
> I have mixed and tested a cone 1 soft stoneware casting slip. It's
> nice and
> strong but it shrinks a little too much and warps a bit too much.
> It's from
> Chappell's book pg.56 of the revised ed. recipe SSC-2:
> But, maybe theres a better Kaolin choice that will bring me closer to
> Chappells results?
> David
Hi David,
Have you tried either EPK or velvacast? They are both non-plastic and
white. Velvacast is usually used in casting slips and is probably the
better of the two for your problem.
Lynn
Lynn Goodman
Fine Porcelain Pottery
Cell 347-526-9805
www.lynngoodmanporcelain.com
David Clark on mon 19 mar 07
Thanks Linda, I also thought I'd try Epk today. I'll have to order the
velvacast
David
Thomas Malone on mon 19 mar 07
Which Imerys kaolin? There are at least 20 that I know of
David Clark on mon 19 mar 07
You know, It only says Imerys English china clay on the bag and Grolleg.
Thomas Malone on fri 23 mar 07
Grolleg is the grade of kaolin and Imerys is the manufacturer
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