Craig Martell on sun 24 mar 02
Hello Chris et al:
This is not an easy question to answer. That's probably why you haven't
received any responses other than Tom Buck's. What did he say
anyway? :>) Also, Ron Roy has been attending a Symposium in British
Columbia and he's probably going to be hammering away at the keyboard any
day now.
I've tried to make clays with a good cross section of particle size for
denser packing. It's kind of tough to do with porcelain but it's not
impossible to make a blend of perhaps 2 to 3 kaolins and a small bit of
ball clay. This facilitates workability in the plastic state and I think
this also aids mechanical strength, as in resistance to fracture and
chipping. I also think that the correct amount of feldspar is important
not only with regard to vitrification but strength as well. With stoneware
clays you want to get enough spar in the body to get the absorbtion down to
about 2.5% and this will promote strength. Any more than this, especially
if you near zero % absorbtion, will cause the body to be too fused and
brittle. Not good! Porcelains can be taken to the near zero point and
still be quite strong. Then you add silica for glaze fit and this needs to
be done with the idea that too much will alter the point of vitrification
and perhaps weaken the body a bit. Jim Robinson's article in Studio
Potter, June 1988, Body Building for Potters gives 10 glazes in the low to
high expansion range that are great aids to finding the correct addition of
silica.
I Took a workshop from Jim Robinson about 20 years ago and we did some
claybody formulation. The strength test was to grip a 3 eights of an inch
thich with pliers on each end and break it in two. We did this with
several mixes and compared the difficulty of breaking. Sort of a backyard
approach but we did get some idea as to what was stronger, or seemed to
be. The idea was to try a lot of different clays that suited your
aesthetics and blends of several to find something that looked good and
performed well.
It's important to remember too that the final result isn't just the
clay. It's clay that has a coating of glass fusion bonded to the surface
of one or two sides of the piece. If you have a strong clay that is coated
with a glaze slightly under compression you will have a very strong
pot. If you have the same strong body that is coated with a glaze the is
under tension and crazing, you will have a weaker pot.
regards, Craig Martell in Oregon
chris clarke on sun 24 mar 02
Every month I get fantabulous magazines with pictures of other potters =
work. Some even have formulas. Ten years ago when I first started =
getting CM, I went nuts. Potters give out their formulas??? Holy crap. =
I was stoked. Ran to the college and started mixing them magic =
numbers. =20
=20
Somehow, my glaze never turned out like theirs. But every month I would =
mix those recipes, every month I would be kind of disappointed to down =
right pissed. Don't get me wrong, I think it's great to share formulas. =
My expectations however were way too high.
It's like when you look through victoria's secret, find a pair of jeans. =
They look great on the model. But when you get them, they kind of =
bunch here and there because you're eight inches shorter then that =
skinny waif.
Clay wears the glaze. If the clay's not right, then the glaze will be =
different. Not always bad, just different. Marriage between the clay =
and the glaze is often over looked.
Now with that said, I only got one response (thank you Mr.Buck) to my =
question about what makes a good strong clay, past all the workability =
stuff. So I'm posting it again. After you find a clay formula, tested =
it, love the way it throws what make you so sure it's a GOOD strong =
clay.
chris
And to the women on the list:
Take a self defense course. Know what it feels like to take someone =
down. Know that your best defense is your instincts. Walk with your =
head up, look around. Not all martial arts rely on formality, Krav Maga =
is based on instinctual reactions. I may be small, but I know what to =
do (running my ass off included in the training).
temecula, california
chris@ccpots.com
www.ccpots.com
Mondloch on sun 24 mar 02
>>After you find a clay formula, tested it, love the way it throws what make
you so sure it's a GOOD strong clay.
>>
Strong in what way?
When I did raku, I used the body- 1part Goldart/ 1partAP Green fireclay/ 1
part 35mesh kyanite. Short as heck and not vitrified but lots of thermal
shock resistance. Now I always add 10-15 % 35mesh kyanite to all my clay.
Might just be in my head but I think it adds strength all down the line-
from wet to fired.
For tile and large wheel work, I like to add a small amount of paper pulp
for green strength and warp resistance. I don't think a small amount has any
significant effect one way or the other on fired strength.
For the intended purposes of my work, I like a body to be vitrified but
still open enough to not be too brittle. So I add feldspar and flint and
then varying proportions of kyanite and grog to open it up.
The only way I know for sure if your clay is strong for it's intended
purpose, is to use the finished work for it's purpose. And don't baby it. Do
anything you can to it that your customers might do. I've had one of our
garden benches out year round for about 10 years now- makes me much more
confident telling my customers that they can stand up to freeze/thaw. Pots
go in the dishwasher and oven, our sinks are used in our own house, vases
are tested with water, et.
Sylvia
I figure I should be good incentive for the younger, thinner gals in my
kick-boxing class. "If that overweight, old lady can try to do this, then I
should sure be able to too!"
---
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
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