Corinne P. Null on tue 28 sep 99
I recently mixed up 10 lbs each of a bunch of different clay bodies, which
sat around for a week, then were wedged and set on a shelf for another week.
Then, rewedged, and though awfully soft and wet feeling yet, I thought l'd
try a plate, just to try it out. Threw like a dream! Decided to go for it
and try a cylinder...flew right up...loose, soft clay, but sturdy. OK, I'll
just buldge it out a little to see if it can take it, and it did - didn't
slump at all! Kept pushing till it started to develop a few cracks - is
that called being short, or immature, or what?
Another batch of a different clay sat for another week, and by the time I
got to it, it had developed a rock hard stubbornness to it. Like bagged
clay.
Give me fresh clay anyday! I'm sure this is all "wrong", but I need to
know... why?
Corinne Null
Bedford, New Hampshire
null@mediaone.net
Mike Gordon on thu 23 aug 01
Hi,
Try Sculpture mix very groggy, and Sculpture mix 412 by Immaco. Mike
Gordon
Gwyn Wahlmann on thu 23 aug 01
Dear ClayArters
I have access to some good clay bodies through local studios, but would
like to find something different. I'm hoping some of you could offer some
recommendations! Here are the qualities I'm looking for:
---already mixed and pugged
---heavy grog/sand content and coarse, rough texture
---cone 10 stoneware (but also good for raku)
---fires to a biscuit or granite colour in cone 10 gas reduction
---for medium-sized sculpture and hand-carving
---from a reliable source and not terribly expensive
Also would like to find something that fits the above descriptions and
would fire white in raku----but not raku clay. (Want to keep firing
temperature options open.) May also be doing salt firing.
Basically, I guess the trick is finding clays that are so heavily
grogged, yet still have some plasticity. I really love the coarse clays
used by Voulkos and some of the wood-firing Japanese potters, but understand
that those clays are more fine-tuned to experienced and personal
specifications/unique to locale than I can expect to just find simply
through retail. Someday I would like to experiment with clay body
development, but being new to all this....eegads.....I have a plethora of
other challenges and basic learning experiences that should probably come
first.
Soldate 60 from New Mexico Clay Inc. looks interesting....
Any suggestions?
Thanks to all who respond, and all who make this discussion group so
invaluable!
Gwyn
Ronda Clark on thu 23 aug 01
I really like Soldate 60 or 30 and have used it in Raku, Pit fire, and ^10
reduction firings. It is soooo plastic and wonderful to throw with! It is
also available from Laguna. I still use it in my pit firings as I can throw
"bigger" with it than I can the raku clay I use.
Ronda
BVCuma on fri 24 may 02
My posted clay body...
I forgot to include
k-feldspar 1/2 part
silica 1/2 part
wallostonite 1/10 part
So a typical batch would be...
exact kgs- aprox parts.
(every batch is slightly altered)
fibre was also wrongly counted at 1%
correctly at .5%
12.5 kg fire clay- 2.5 part
10 kg china clay- 2 part
10 kg ball clay-2 part
5 kg red clay- 1part
5 kg unknown plastic grey clay- 1part
2.5 kg silica 1/2 part
2.5 kg k-feldspar 1/2 part
1 kg wollastonite 2%
.5 kg bentonite 1%
.5 kg ulexate 1%
.5 kg kyanite 200 mesh 1%
5 kg 35's kyanite or 10%
.25 kg cotton fibre or .5%
This yeilds a somewhat short but robust
and sturdy body that I consider...
execellent for throwing
below average for handle pulling
and good for sculpting.
Generally serves my purposes at the moment...well.
Supplier was able to provide analysis on all
major components except...fireclay
I expected soaked slop (fully wetted) to improve plasticty
but a comparison of wedgable and slop
from same batch ... aged six months
to be non comparable in plasticity...
storing as slop was unimproved in anyway.
And by chance came across this quote recently
from Rhodes Stoneware and Porcelain:=20
The Art of High Fired Pottery (1959 copyright : )
Page 52...
Clay bodies tend to be quite short
and not satisfactory to work=20
until they have aged for at least a few days.
The beneficial effects of this early aging
is no doubt due to the more thorough=20
wetting of the clay particles.
But oddly enough, aging does not seem to begin
until the clay body is in the plastic condition,
and clay when it is in slip form does not seem to=20
gain much in workability from age.
I can corfirm this as true
Further more on page 61
"Stoneware based on Fire clay"
4 part fire clay=20
3 part ball clay=20
1 part red clay=20
1 part flint=20
1 part feldspar
He goes on to say...
This type of body,=20
because of the large portion of fire clay,
is relatively coarse,=20
and may not be ideal for wheel work.
It is good for modeling or building.
The kind of fire clay used is critical in this compostion,
and if a plastic one is available,
a body of this sort maybe very good to work with.
I am glad to see more discussion on clay bodies
as is often overlooked aspect of ceramics with junior workers...
and is therefore my foundation and focus at the present time.
Bruce
ps my math is weak
and I'm very tired
so please correct
me if I've made a mistake
in cross calculations
=20
Clayart SCtag on mon 21 apr 08
are these fireclays still available?
In a message dated 4/21/2008 5:50:10 P.M. Eastern Daylight Time,
BILLM@PCADMIN.CTC.EDU writes:
Dave Shaners '68 clay body
10 Custer spar
70 AP Green Mexico Fireclay
50 Hawthrone Bonding clay
25 Tennessee ball clay
Wellsville Fire clay
A bit of fine grog
=20
**************Need a new ride? Check out the largest site for U.S. used car
listings at AOL Autos.
(http://autos.aol.com/used?NCID=aolcmp00300000002851)
Bill Merrill on mon 21 apr 08
The best clay bodies will be those bodies that have clays in them that
are of different particle size. Talc has been said to be the blame of
everything under=20
The sun when it comes to clay body problems. A good cone 10 body would
have a plastic ball clay in it. I use several clays to make up 30
parts of the body.
A coarse fire clay with give the body tooth, A.P. Green Mexico Fire clay
is what I use to... 20-25 parts of fireclay. As the base clay 25 parts
of Cedar heights=20
Gold Art works well. For color I use Muddox Neuman red 15-20 Parts. The
filler is a good grog if you can find one. I generally use 5-!0% grog
depending on what I'm making. The flux I use is Desert 51 Talc. Talc
makes the clay have a rich orange color because of the MGO in the Talc.
I use 7% talc. For those of you who don't use Talc, use Custer
Feldspar. Either way 7% works. This body is one of the toughest, good
color bodies you could use at cone 10. Many commercial bodies throw
like they're made from Teflon, they're so slippery and don't stand up
well.
=20
We are at the mercy of suppliers for what we use, so be particular.
Develop a body to suit your needs. Clay bodies can be simple or
complex. Here's one Dave Shaner gave me the following clay body in May
of '68. Dave could throw anything. His glazes seemed to work well with
out much iron in his body. When he purchased clay for the Bray he got
clay that was inexpensive , yet did what he wanted. One of clay bodies
he used had a tendency to crack when drying. He added a cup of additive
a to 100 pounds of clay. It was like molasses and made the greenware
extremely had. It was a way for him to utilize the he had on hand.=20
=20
Additive A Benefits:] Additive A is the by product of a wood pulp
process.
Improved clay workability
Reduced need for die lubrication
Increased extrusion rate
Increased life of wearing parts
Increased green strength=20
Reduced free water
Faster drying rates
Reduced energy consumption
Flexibility to use less plastic clays".
=20
=20
Dave Shaners '68 clay body
10 Custer spar
70 AP Green Mexico Fireclay
50 Hawthrone Bonding clay
25 Tennessee ball clay
Wellsville Fire clay
A bit of fine grog
=20
Try other clays than what is offered from the suppliers. You won't be
sorry you do!!
=20
Bill
=20
=20
=20
=20
=20
=20
=20
=20
=20
Ron Roy on thu 27 aug 09
A couple of comments about testing clays - seems just about everyone does i=
t
their way - I can tell you - from the different testing I have done - it
does not take much to get misleading numbers - even putting the fired clay
into the boiling water while still hot from the kiln makes a difference.
I boil all clay bars for two hours - according to Dan Rhodes instructions
in Clay and Glazes for the Potter. Always have - always will - because data
is for comparing and you don't want to change horses in that stream.
What Dan left out was - if you don't cool the bars before weighing them -
some of the water will evaporate and give a false reading. He specifies the
bar size as well and that should be standard if you want to compare data
from clay to clay.
Anyone who wants to compare their absorption rates with my data - (20 years
and 40 bodies worth) should boil for 2 hours - I will send anyone detailed
instructions on testing clays - just send me an email.
It really is important - most clay makers don't test each batch every time
they are mixed and therefore don't know how far their clays have drifted
from the last time they tested. If you really want to know if your pots are
going to leak you have to test - and it's not hard, or time consuming or
complicated - it's easy.
RR
On Tue, Aug 25, 2009 at 7:46 PM, lili krakowski wr=
ote:
> Sometimes there is only the customer "to blame". Sorry about that.
>
> Many manufacturers/suppliers list clay bodies they produce as c.4 to c 6.
> OR c.5-c.8.
> Some include an absorption % as a guide to how mature the body is at a
> particular cone. As far as I can tell, some suppliers are more accurate
> than others. And remember: the manufacturer knows all I list below--and
> probably "allows" another cone or two atop the listed high point--in case
> YOUR kiln says c.8 when actually it went to c.9.
>
> This has nothing to do with the actual firing/firing temp/firing range. =
I
> own some functional ware fired to a hot c.10 that is more porous than my
> c.6. I have some old c.4 ware from my student days--Fetzer and Dalton cl=
ay
> mix plus whatever--that is non absorbing and non leaking.
>
> When you buy a body listed as c.4-8 it will hold up at c.4 and be mature =
at
> c.8. As kilns do not heat evenly, and some people rely entirely on the
> sitter cone, not the visual ones, and do not adjust for the difference
> between the two (common). It's a wide open range out there. In other wor=
ds
> if someone's big old kiln fires unevenly and the c. in the sitter is c.6
> because that is the temp at which the clay is supposed to be pretty
> vitrified....the kiln actually may fire to c.4 here and c.5 there....and =
to
> c.6 ONLY in the sitter.
>
> As much as I truly love conspiracy theories this is NOT a conspiracy.
> Every clay body requires, nay, demands, testing in every kiln one uses.
> And every firing method.
>
> This uneven result from diverse kilns, diverse cones in the sitter, diver=
se
> heating and cooling, diverse firing method makes it imperative that every
> body be tested.
>
> Test every body for workability at YOUR method of working.
>
> Make a simple test bar.
> This is easy to do. Buy a centimeter ruler whose figures are RAISED. I
> get mine at sewing and knitting stores. Make a little bar about 1/4"
> thick and impress the ruler on it, so that the clay is imprinted with the
> marks for 1-10 centimeters.
>
> Write name of clay body on bar, dry, fire to your intended glaze temp.
>
> Measure the bar and record the shrinkage. Figure out what the % of
> shrinkage is.
>
> Now make some small test pots or bars. Bisque and weigh them. They do n=
ot
> all have to be the same weight, but you do need to identify what is what.
>
> Glaze fire them. I prefer to fire them unglazed.
>
>
> Dispose them in different parts of your kiln, and make a chart or similar
> record who is where. For these tests I like to put a self-supporting con=
e
> next to each test. Record where it is hotter, where cooler.
>
> After the firing weigh the pieces again. And record the weight. Now pla=
ce
> the tests in water and boil. People vary in opinion about how long to bo=
il.
> I cook'em along with some 6 medium potatoes and when they are done my te=
sts
> are "done" (At least1/2 hour)
>
> Fish the tests out, one by one. Dry each test briefly on a towel, and
> weigh the test. The weight difference between the weight when glaze=3Dfi=
red,
> and the weight glaze-fired-and-boiled give you the absorption %. I follo=
w
> Rhodes's rule of not more than 1.5%.
>
> This is both tedious and boring. But it saves a lot of heartache.
>
>
>
> Lili Krakowski
> Be of good courage
>
--
Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0
Bill Merrill on mon 23 nov 09
Here is an article that is very good on clay bodies from Ceramic =3D
Industry that helps with understanding how clays are selected, blended =3D
and used to obtain the optimal forming, drying and firing properties is =3D
an important part of making high-quality pottery. There is some good =3D
advice here.
=3D20
=3D20
http://www.ceramicindustry.com/Articles/Feature_Article/4bb54af4d2ac7010V=
=3D
gnVCM100000f932a8c0____
=3D20
There is no such thing as fast food ceramics. You don't get experience, =
=3D
you have to live it.
=3D20
Bill Merrill
claybuds@ATT.NET on wed 25 nov 09
Bill,
Thanks very much for the Jonathan Kaplan article on clay bodies. Indeed, al=
ot of good solid advice.
Jonathon states that casting bodies require a plastics to non-plastics rati=
o of 50:50. "This ratio can deviate slightly, but not by much."
Well Jonathan, here we go again! I'm after a cone 10 reduction casting por=
celain body. If anyone is interested in the results, let me know.
David Beumee
Lafayette, CO
-------------- Original message from Bill Merrill : =
--------------
Here is an article that is very good on clay bodies from Ceramic Industry t=
hat helps with understanding how clays are selected, blended and used to ob=
tain the optimal forming, drying and firing properties is an important part=
of making
> high-quality pottery. There is some good advice here.
>
> http://www.ceramicindustry.com/Articles/Feature_Article/4bb54af4d2ac7010=
VgnVCM10
> 0000f932a8c0____
> There is no such thing as fast food ceramics. You don't get experience,=
you
> have to live it.
>
> Bill Merrill
Rimas VisGirda on wed 5 may 10
There's been a lot of hubba-bubba about commercial clay bodies lately, whic=
h to use, what's best, what's better, ad infinitum... Cone 6, cone 9, addin=
g ball clay to recycle, etc., etc. The current issue of Ceramics TECHNICAL =
has a very good article delineating the factors in determining a commercial=
body and a very clear and concise analysis of the factors involved. The ar=
ticle is by Jeff Zamek and titled "Mass Production Pre-Mixed Clays" and app=
ears in Ceramics TECHNICAL #30, May-October 2010. Regards, -Rimas
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