vince pitelka on thu 7 mar 02
> After three days of milling the sound of the marbles was very noticeable.
> When I opened the rock tumbler, the slip inside was quite watery - more
the
> consistency of milk. This was completely opposite of what I expected. I
did
> the settling test again and after a day of settling, there was a definite
> intermediate layer and the water layer was still cloudy - both good
> indications that the clay was being broken into smaller pieces.
> Here's the question - Why did the slip become less viscous rather than
more
> viscous? Any guesses?
Bruce -
I think Ivor explained this phenomenon earlier this evening. As a result of
the physical breakdown of particles in the ball mill, the feldspar in your
porcelain body released alkalinity into solution, deflocculating the slip,
causing it to thin noticeably.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Bruce Girrell on thu 7 mar 02
Recently one of my experiments turned out a little differently than I had
expected. As I reported in the thread "what are YOU up to," I am engaged in
experiments to improve the results in the porcelainous clay body that we use
for our pots. For one of these experiments I decided to ball mill some of
our clay to be able to separate out the finest particles.
I took about a pound of clay and tore it into small chunks which I threw
into a blender with water to create a slurry. I placed the slurry into a
rock tumbler with a couple pounds of marbles (some large, mostly small). I
was concerned about the viscosity of the slurry. I imagined that as the clay
particles got broken apart there would be substantially more clay surface
area exposed which would bind more water, resulting in a "thicker" or more
viscous slip. The viscosity of slurry that I started with was on the order
of thick cream.
When I started milling, the rock tumbler was almost silent. After a day of
milling there was little change. A sample of the slurry, mixed with water in
a graduate and shaken, settled into two distinct layers in a matter of an
hour or so.
After three days of milling the sound of the marbles was very noticeable.
When I opened the rock tumbler, the slip inside was quite watery - more the
consistency of milk. This was completely opposite of what I expected. I did
the settling test again and after a day of settling, there was a definite
intermediate layer and the water layer was still cloudy - both good
indications that the clay was being broken into smaller pieces.
Here's the question - Why did the slip become less viscous rather than more
viscous? Any guesses?
Bruce "mystified" Girrell
Des & Jan Howard on fri 8 mar 02
Bruce
You said that marbles were used for the grinding balls.
What's the bet that the intensive grinding released
sodium from the glass & deflocculated the clay?
Des
Bruce Girrell wrote:
> After three days of milling the sound of the marbles was very noticeable.
> When I opened the rock tumbler, the slip inside was quite watery - more the
> consistency of milk. This was completely opposite of what I expected. I did
> the settling test again and after a day of settling, there was a definite
> intermediate layer and the water layer was still cloudy - both good
> indications that the clay was being broken into smaller pieces.
>
> Here's the question - Why did the slip become less viscous rather than more
> viscous? Any guesses?
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
iandol on fri 8 mar 02
Dear Bruce,
You are deflocculating your clay. The deflocculant is coming from the =
marbles, a soda rich glass. There will be sufficient abrasion from the =
residual silica in your clay to cause this. Make up some marbles shapes =
from a good quality porcelain and fire it hard. You should then find =
that more water is needed as you predicted.
Have fun.
Best regards,
Ivor
| |
|
