primalmommy on sun 12 jun 05
I have read that I can use a porcelain body to make decorating slip for
^6 pots. I have quite a lot of porcelain lying around -- a batch I
bought years ago from a potter who later told me it was contaminated
with chunks of something. I had put it in buckets of water thinking I
could sieve it all but then I got real.
Now I am experimenting with small amounts of it, sieved, as decorating
slips. Why will it work on ^6 ware, though? Why won't it be just bisqued
at those temps, while the underlying clay body is vitrified? Why, with a
different firing temp, won't it just crack and fall off?
Maybe it will. Nothing is fired yet. But can anybody explain how ^10
porcelain can work on the surface of a ^6 body?
Thanks.
Yours
Kelly in Ohio
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Snail Scott on mon 13 jun 05
At 09:15 PM 6/12/2005 -0700, you wrote:
>...can anybody explain how ^10
>porcelain can work on the surface of a ^6 body?
Darn near anything will work if it's thin enough.
Also, porcelain shrinks more than most stoneware,
so although it's technically underfired, the
shrinkages at ^6 may be quite similar. And, since
we expect porcelain to be more vitrified at its
maturity temperature than any stoneware would be
at its own maturity, they may be more similar at
^6 than you might think.
Consider the porcelain to be a fine-grained white
engobe. In fact, compare a few porcelain recipes
to a few engobe recipes - might be quite a lot
of corresponence.
I've never tries this (though I've used ^6 porcelain
casting slip as an engobe), but I think it's worth
a try.
-Snail
jesse hull on mon 13 jun 05
You used the word "bisqued" - are you thinking of ^06,
perhaps?
Either way, the temp. difference b/t ^6 and ^10 aren't
worlds apart...
I use a white grolleg body that could easily stand ^15
or so, but only fire it to 2350F, and ramp so fast
that the peak temp. can't be called ^10. Whether my
clay be termed Porcelain or not depends on your
definition, really. Some catagorize by the
ingredients, others by both that and the level of
vitrification.
I don't argue, -I just like what comes out of my kiln.
As for whether yours will work, I think it should be
ok. If not, just dry out the clay, pulverize, weigh,
and mix in a bit of flux to bring the vitrification
point down a bit.
~jessehull.
www.jessehull.com
www.latticestructures.com
Paul Herman on mon 13 jun 05
Hi Kelly,
You asked:
Why will it work on ^6 ware, though? Why won't it be just bisqued
> at those temps, while the underlying clay body is vitrified? Why, with a
> different firing temp, won't it just crack and fall off?
It might work OK. At cone 6, the porcelain slip will be more vitreous
than bisque. There is only 140F difference between cones 6 and 10. As
for it flaking off, as usual, you just have to test it. If it dried on
the work and hasn't flaked that's a good sign, you're halfway there!
best wishes,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
John Rodgers on mon 13 jun 05
I work with cone 6^ porcelain all the time. I think you are right. I
don't think cone 10 porcelain as a slip will work. You will have bisque
on a vitrified body underneath...... and ultimately something you don't
want. And it will prol'ly flake off.
There are those on this list with more experience than I who can prol'ly
tell you what to add to the C-10 porcelain to lower the point of
vitrification to that of the body underneath. It is beyond my scope,
but we do have such knowledgeable folk out there.
regards,
John Rodgers
Chelsea, AL
primalmommy wrote:
>I have read that I can use a porcelain body to make decorating slip for
>^6 pots. I have quite a lot of porcelain lying around -- a batch I
>bought years ago from a potter who later told me it was contaminated
>with chunks of something. I had put it in buckets of water thinking I
>could sieve it all but then I got real.
>
>Now I am experimenting with small amounts of it, sieved, as decorating
>slips. Why will it work on ^6 ware, though? Why won't it be just bisqued
>at those temps, while the underlying clay body is vitrified? Why, with a
>different firing temp, won't it just crack and fall off?
>
>Maybe it will. Nothing is fired yet. But can anybody explain how ^10
>porcelain can work on the surface of a ^6 body?
>
>Thanks.
>
>Yours
>Kelly in Ohio
>
>
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Chris Campbell on mon 13 jun 05
Kelly -
I cannot give you a technical explanation but I
can say that I do it all the time and nothing bad
happens.
I have a cheaper clay that I use for large hanging tiles ...
sometimes I cover the whole surface with the Southern Ice
porcelain slip to make it brilliant white.
Works like a charm ... thick or thin ... globbed on or
layered .. with and without paper ... colored with Mason
Stains or plain.
I'm afraid if I knew why it worked it would begin to fail
because I was thinking too hard. (grin)
Chris Campbell - in North Carolina - is there anything better than
messing with clay !!!
Chris Campbell Pottery LLC
9417 Koupela Drive
Raleigh NC 27615-2233
Fine Colored Porcelain since 1989
1-800-652-1008
Fax : 919-676-2062
website: www.ccpottery.com
wholesale : www.wholesalecrafts.com
Carol Tripp on tue 14 jun 05
See pages 102-103 in Vince P's 'Clay, A Studio Handbook' where he discusses
using a ^10 porcelain body as a slip - he gives a recipe and calls it
All-Temperature Slip. I've used to on my Tuckers ^6 without problems.
Best regards,
Carol
Dubai
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Vince Pitelka on tue 14 jun 05
For the last 20 years I have often used an "all temperature slip" recipe,
which should be a flawed concept, but in practice it has worked well with
very few problems. It is jreally ust a cone 10 porcelain recipe:
All-Temperature White Slip Base
Kaolin ------------------ 32
Potash Feldspar ---- 26
Ball Clay --------------- 19
Flint --------------------- 18
Borax -------------------- 5
Total ------------------ 100
Plus:
Zircon Opacifier ------ 8
The only modification I have made over the years is the addition of 5%
borax, which helps with adhesion through the early stages of red heat,
decreasing the chance of the slip separating or lifting from the surface.
In "Clay and Glazes for the Potter", the old studio pottery bible, Rhodes
gives a table of slip recipes varied according to firing temperature and
according to application to greenware, bone-dry, or bisque-fired. Most
ingredients vary, but the recipes all include 5% borax.
One thing I question in his table of recipes - he gives different recipes
for application to bone-dry and bisque-fired, and I don't think that is
necessary. An ordinary clay slip for application to damp clay is not
appropriate for application to bone-dry or bisque-fired work, but a properly
formulated engobe with more non-plastics should work equally well on both
bone-dry and bisque-fired work.
I think that the above recipe is fine for midrange and high-fire
temperatures. If I were doing low-temperature functional work, I would
formulate a white base slip with some 3134 frit to achieve a denser fired
coating. For non-functional work it won't make any difference.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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