Paul Borian on mon 9 jun 08
I need to modify my clay body so it can dry very fast without cracking,
especially since I have a/c in the studio now and it will probably by
running all summer so the pots dry fast, plus I generally put them into
the bisque kilns when they are leather hard. I believe that many people
add sand to the clay body to help accomplish this - is that correct? Are
there disadvantages to using sand? I recall reading a long time ago that
it can cause dunting but I don't know to what extent.
I would be interested to hear from anyone else using it.
Thanks,
Paul
Hank Murrow on tue 10 jun 08
I agree with what david reports here about the use of sand in clay
bodies. One thing I have found quite acceptable is milling bisque of
the body in question, which I grind in my Mini-Mill to the size I
want and wedge this into my body when preparing for throwing. The
particles are not round, you can get the exact size you want, and the
color after the firing is the same as the plastic body. Easy manual
cleanup with my 80 grit Alumina sanding belts, followed by my diamond
laps.
Cheers, Hank
On Jun 10, 2008, at 7:13 PM, David Hendley wrote:
> Through the years I have used claybodies that
> contained sand, and have come to the conclusion
> that I just don't like it.
>
> First of all, clay with sand seems to go from OK to
> too wet very fast. This makes it much harder for
> beginners working on the wheel. Even pros will
> find it more challenging to throw big fat round
> shapes.
>
> Also, there is sand and there is sand. Sharp angular
> sand works better (more like grog) than sand made
> up of rounded particles. A body with round sand
> will tend to slump while throwing.
>
> Then, once fired, the surface character of the clay
> is often not pleasing. It's as if the sand particles
> are on the surface, causing a slightly bumpy rather
> than a smooth finish. Also, generally, a body with
> sand in it does not work well for atmospheric or
> wood firings.
>
> If my local supplier did not carry a suitable grog
> I would pay the high shipping cost of having grog
> shipped to me before I would use sand as a temper
> or "opening" ingredient.
>
> David Hendley
> Maydelle, Texas
> david(at)farmpots(dot)com
> http://www.farmpots.com
>
Lee Love on tue 10 jun 08
Mashiko clay is naturally sandy. It is found between two layers of
yellow sand. We used it for covers for the stoke holes on the
noborigama. Probably a good raku clay too.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"We are such stuff as dreams are made on, and our little life is
rounded with a sleep." --PROSPERO Tempest Shakespeare
Michael Wendt on tue 10 jun 08
Paul,
I used to use sand but found it to be tricky
since too much lead to firing cracking
at red heat. It also made the clay short.
For the past three years, I have been using
DRA-10C, a long chain polyethylene polymer
that is a food grade additive to beer (stabilizes the
foam ). At 25 parts per million, it acts as a
flocculant, drag reducing agent and a kind of
reinforcer which has substantially lowered our
cracking in speed drying applications without
the need to add sand or grog.
I believe the long chains act like rebar during
drying ( they are as long as 1,000,000 molecular
units !). Think of how this can strengthen a body
and prevent cracking.
As to safety, this material has FDA approvals
for many food applications and as an ingredient
in wound dressings.
We are the authorized distributor.
Call me if you would like to try some.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
Paul wrote:
I need to modify my clay body so it can dry very fast
without cracking,
especially since I have a/c in the studio now and it
will probably by
running all summer so the pots dry fast, plus I
generally put them into
the bisque kilns when they are leather hard. I believe
that many people
add sand to the clay body to help accomplish this - is
that correct? Are
there disadvantages to using sand? I recall reading a
long time ago that
it can cause dunting but I don't know to what extent.
I would be interested to hear from anyone else using
it.
Thanks,
Paul
Steve Mills on tue 10 jun 08
My understanding has always been that opening up a body, be it with sand, grog, etc. would help it to withstand being fast dried,
HOWEVER,
from personal experience I know that the clay I currently use (which contains approx. 10% Molochite) and ANY other body containing various degrees of "temper" that I've used and abused have all dried very quickly using my favoured technique of two electric fans at max speed pointing at it from opposite sides without stress or fracture.
Leather Hard to Bone Dry 6 hours max!
So what I'm saying in my usual rambling roundabout way is; apply the Potter's standard rule-finding process and "suck it and see!"
George Bernard Shaw said: "The Golden Rule is; there are NO Golden Rules!"
I rest my case M'Lud.!
Steve
Bath
UK
--- On Tue, 6/10/08, Paul Borian <Paul@DOCRET.COM> wrote:
From: Paul Borian <Paul@DOCRET.COM>
Subject: Sand in a stonware body - advantages, disadvantages?
To: CLAYART@LSV.CERAMICS.ORG
Date: Tuesday, June 10, 2008, 3:24 AM
I need to modify my clay body so it can dry very fast without cracking,
especially since I have a/c in the studio now and it will probably by
running all summer so the pots dry fast, plus I generally put them into
the bisque kilns when they are leather hard.
Fredrick Paget on tue 10 jun 08
>I need to modify my clay body so it can dry very fast without cracking,
.............
>Paul
While it is not sand in stoneware, this may possibly work for you
too, along with some grog..
I was having a lot of trouble with the imported porcelain "Southern
Ice".Such as lack of plasticity, cracking on drying, and low green
strength and sagging during throwing if too thin.
I recently downloaded and read some interesting pdf papers from
Zschimmer and Schwartz of Germany about their Peptapon gums - a
series of products that are CMC on steroids with higher molecular
weight. These gums do amazing things to the rheological properties of
clay and glazes. They suspend particles in glazes without requiring
thickeners.
The pdfs
have German titles but are in English. Unfortunatly Peptapon is
generally not sold in the USA and the factory in Germany puts it up
in 25 kilo bags only..
Something went click click in the noodle and I remembered that bag of
powder I bought at NCECA called "Magma". I don't know where Bracker
gets this product but this is similar to a Peptapon gum in its
action.
So I put some "Magma" into the Southern Ice by wedging in a level
teaspoon in 10 pounds of clay and the clay became much more
manageable. Much less cracking on drying. I even tried drying some
flat tiles in the sun. They had a tendency to curl up due to uneven
drying, but no cracking.
The action of the gum is to let the clay move when you apply a force
to it but it sort of freezes into the position you last leave it in
when the force is stopped.
It also increases the green strength when drying, so less cracking.
The treated clay may not keep long unless a preservative is used.
Some of the Peptapons have an included preservative.
--
Fred Paget
Twin Dragon Studio
Mill Valley, CA, USA
fredrick@well.com
Charter Member Potters Council
Paul Borian on tue 10 jun 08
Michael,
do you know why sand causes cracks? At what percentage did the body
start to crack more?
=20
i basically just want to increase the non-plastics by about 5% and i am
already using 10% mullite but it is pretty harsh stuff - very sharp and
often leaves sharp spots on the finished pots if the glaze was just a
little thin in one area, especially the bottom or the rims. So i don't
want to increase it and i don't have many other options for grog from my
supplier. But if it is likely to cause firing cracks then i may have to
figure something else out.
=20
thanks,
paul=20
Paul Herman on tue 10 jun 08
Hi Paul,
I use sand in a couple of my clay bodies, and have not experienced any
dunting problems.
A lot depends on the sand you are using, and as you can imagine all
sands are not created equal. The kind I use now is 80 mesh silica sand
from Laguna Clay Co. 80 mesh is so fine you hardly notice it when
throwing. I have successfully used 60 mesh foundry sand from Overton
Nevada also, up to 12% in the body. In college we got some new sand
that had a lot of feldspar in it, and it ruined a lot of clay and
claywork. Test it well.
Mullite is very nasty sharp stuff. Have you tried to find some fine
white grog?
Best wishes,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Jun 10, 2008, at 4:37 PM, Paul Borian wrote:
> Michael,
>
> do you know why sand causes cracks? At what percentage did the body
> start to crack more?
>
>
>
> i basically just want to increase the non-plastics by about 5% and i
> am
> already using 10% mullite but it is pretty harsh stuff - very sharp
> and
> often leaves sharp spots on the finished pots if the glaze was just a
> little thin in one area, especially the bottom or the rims. So i don't
> want to increase it and i don't have many other options for grog
> from my
> supplier. But if it is likely to cause firing cracks then i may have
> to
> figure something else out.
>
>
>
> thanks,
>
> paul
>
David Hendley on tue 10 jun 08
Through the years I have used claybodies that
contained sand, and have come to the conclusion
that I just don't like it.
First of all, clay with sand seems to go from OK to
too wet very fast. This makes it much harder for
beginners working on the wheel. Even pros will
find it more challenging to throw big fat round
shapes.
Also, there is sand and there is sand. Sharp angular
sand works better (more like grog) than sand made
up of rounded particles. A body with round sand
will tend to slump while throwing.
Then, once fired, the surface character of the clay
is often not pleasing. It's as if the sand particles
are on the surface, causing a slightly bumpy rather
than a smooth finish. Also, generally, a body with
sand in it does not work well for atmospheric or
wood firings.
If my local supplier did not carry a suitable grog
I would pay the high shipping cost of having grog
shipped to me before I would use sand as a temper
or "opening" ingredient.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> I need to modify my clay body so it can dry very fast
> without cracking,
> especially since I have a/c in the studio now and it
> will probably by
> running all summer so the pots dry fast, plus I
> generally put them into
> the bisque kilns when they are leather hard. I believe
> that many people
> add sand to the clay body to help accomplish this - is
> that correct? Are
> there disadvantages to using sand? I recall reading a
> long time ago that
> it can cause dunting but I don't know to what extent.
Kim Hohlmayer on wed 11 jun 08
Dear Paul H.,
I was very interested in the last line of your reply to the sand question. When I fired at cone 10 I used Standard Ceramic Supply #181 which I thought had mullite to make the body less susceptible to thermal shock without using grog. The idea was to get an high-fire body for oven style ware without the roughness of grog. I used it for tiny sculptures because the smoothness let me work in super fine detail while it still had the toughness
to keep all the little parts from cracking both before and during firing. A grogged body I had been using kept showing tiny cracks after the final glaze firing no matter how wonderfully I had followed all the holy rules of attatching one piece of clay to another. The 181 never once gave me that problem and as I said was very smooth.
So, does mullite come in "sharp" and "not so sharp" versions (dif. mesh)? Or am I totally wrong about mullite in the #181? Goodness knows I have been wrong many times in my life about many things. Anyway, if you or anyone else can clear up my confusion, I would be very thankful. --Kim H.
--- On Tue, 6/10/08, Paul Herman <potterpaul@FRONTIERNET.NET> wrote:
From: Paul Herman <potterpaul@FRONTIERNET.NET>
Subject: Re: Sand in a stonware body - advantages, disadvantages?
To: CLAYART@LSV.CERAMICS.ORG
Date: Tuesday, June 10, 2008, 9:41 PM
Hi Paul,
I use sand in a couple of my clay bodies, and have not experienced any
dunting problems.
A lot depends on the sand you are using, and as you can imagine all
sands are not created equal. The kind I use now is 80 mesh silica sand
from Laguna Clay Co. 80 mesh is so fine you hardly notice it when
throwing. I have successfully used 60 mesh foundry sand from Overton
Nevada also, up to 12% in the body. In college we got some new sand
that had a lot of feldspar in it, and it ruined a lot of clay and
claywork. Test it well.
Mullite is very nasty sharp stuff. Have you tried to find some fine
white grog?
Best wishes,
Paul Herman
Ron Roy on thu 12 jun 08
There is a reveling micro photo in Ceramic Master Pieces - if a chunk of
silica in a clay body. When that piece of silica went through the quartz
inversion at 573C - during cooling - it went from beta quartz to alpha
quartz - with a decrease in size. You can see the gaps around the quartz
crystal left when the crystal contracted.
I'll be happy to scan the photo if someone will put it up somewhere.
Not such a bad thing when you consider that any cracks in the body will
stop when they contact those gaps. Still - it is clearly unsettling to see.
The extra silica will help control crazing but will increase the chance of
shivering and dunting with low expansion glazes.
It will also encourage bisque dunting at 573C due to uneven cooling of
ware. If you make big pots the problem gets worse.
I have mixed clays for others with sand in them - and Tuckers sells several
with sand - so it is possible to do it. I would recommend graded sand - not
a mixture of fines and larger - especially if you are firing at higher
stoneware temperatures.
I think a better solution is grog - more open and will let more water
through faster - Mulcoa seems to be the way to go. Some of the other grogs
have some lime pop issues so be careful and watch for the problem.
Email me off line if there are questions.
I'll be happy to scan the photo if someone will put it up somewhere.
RR
>Michael,
>
>do you know why sand causes cracks? At what percentage did the body
>start to crack more?
>
>
>
>i basically just want to increase the non-plastics by about 5% and i am
>already using 10% mullite but it is pretty harsh stuff - very sharp and
>often leaves sharp spots on the finished pots if the glaze was just a
>little thin in one area, especially the bottom or the rims. So i don't
>want to increase it and i don't have many other options for grog from my
>supplier. But if it is likely to cause firing cracks then i may have to
>figure something else out.
>
>
>
>thanks,
>
>paul
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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