louroess2210 on thu 16 mar 06
> Can a slip be usable for both wet and dry pieces? I thought the
> shrinkage between wet and dry would preclude that. I know there is
> no more shrinkage from bone dry to bisque so a slip can be used on
> either. I thought a slip could be for wet and leather hard OR
> dry and bisque, but not both. Thanks,
> Lou in Colorado
Ron Roy on fri 17 mar 06
Hi Lou - I have not answered because I don't use much slip aside for slip
made from the bodies I use.
Much depends on the clay you use - how strong it is as it dries - the most
amasing slip i have ever used is from Jeff Oestreich - 95% ball clay (I
used Bell dark) and 5 % red iron - or was it 90 ball and 10 red iron - and
it stuck to anything from soaking wet to dry - even the wall - without
cracking.
The best advice I can give is to deflocculate your slip - that cuts the
shrinkage way down and stops the cracking.
There can be issues when a slip has too different a COE than clay and glaze
- certainly makes it more complicated bonding three materials instead of
two - thats why using the same clay as the body is a no brainer.
Best to so some serious testing before making a bunch of slipped pots - use
the slip thick if you want to find any fit problems.
RR
>> Can a slip be usable for both wet and dry pieces? I thought the
>> shrinkage between wet and dry would preclude that. I know there is
>> no more shrinkage from bone dry to bisque so a slip can be used on
>> either. I thought a slip could be for wet and leather hard OR
>> dry and bisque, but not both. Thanks,
>> Lou in Colorado
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
lee love on fri 17 mar 06
--- In clayart@yahoogroups.com, louroess2210 wrote:
> Can a slip be usable for both wet and dry pieces? I thought the
> shrinkage between wet and dry would preclude that. I know there is
> no more shrinkage from bone dry to bisque so a slip can be used on
> either. I thought a slip could be for wet and leather hard OR
> dry and bisque, but not both. Thanks,
> Lou in Colorado
Hi Lou,
Rhodes' slip was designed to act like a normal slip on leat=
her
hard, but Jeff Oestrich thought "outside the box" and tried it on
bisqued ware and found that it cracked nicely, having a similar feel
to traditional crawling glazes. It is what you get if you drop the
fetish for control. ;^)
I liked using it under Sander's Tamba glaze. The glaze is
translucent where thin and the crackle slip helps the glaze go on thin
and helps slow the runs. I like it in soda too, but will run more so
the pot needs to be on shells or wads.
Sander's Tambe called for Michigan slip, but I subbed Alberta slip:
Alberta Slip 60
Wood ash 40
R.I.Ox 5%
--
Lee In Mashiko, Japan
http://mashiko.org
http://seisokuro.blogspot.com/
"I have been impressed with the urgency of doing. Knowing is not
enough; we must apply. Being willing is not enough; we must do."
--Leonardo da Vinci
lee love on sat 18 mar 06
--- In clayart@yahoogroups.com, Ron Roy wrote:
> two - thats why using the same clay as the body is a no brainer.
One of the main reasons for not using the clay body in the slip, is
that traditionally, a lighter slip is often used over a darker body.
It is a way to have a white surfaces for the glazes by using a thin
coat of the more exprensive white clay, rather than having to make the
body from the white clay.
Mashiko is an exception to this, the clay body being of a
lighter color, Traditionally, an ocher slip is used over the body.
The slip is made of 100% local ocher clay. Never seems to be a
fitting problem.
All applications are at leather hard.
--
Lee In Mashiko, Japan
http://mashiko.org
http://seisokuro.blogspot.com/
"Cooking and art can never be understood, however high your status and
qualifications may be. That is how difficult they are. And yet
nothing else in life is so important." -Rosanjin.
John Britt on sat 18 mar 06
Lee,
--- In clayart@yahoogroups.com, Ron Roy wrote:> two - thats
why using the same clay as the body is a no brainer.
Although it is a good idea to keep thinkgs simple, I don't think it is
a "no brainer".
There are many reasons someone would use a different clay body as a slip.
For example: if you worked in a group situation where there where multiple
clay bodies being used. Like in an Art Center, Community College,
University, etc. Or if you wanted a different colored slip, like you said,
or if you wanted to use multiple colors in your slip.
Another reason would be if you wanted to apply the slip to bisque. For
example: if you wanted to use multiple colored slip and stains with a
cover glaze. Or if you wanted a flashing slip for soda, salt or wood
firing.
Sculptors often use very groggy bodies or bodies with nylon fibers and
like a smooth slip, or they even like to use terra sig. after bisque
firing.
I am sure that there are many other reasons, that I haven=92t listed, to
make up a slip other than your clay body.
John Britt
www.johnbrittpottery.com
Ron Roy on sun 19 mar 06
In the end it depends on what you want to do with a slip or engobe - if
what you want to do is add texture - as I have done on the pots in
Mastering cone 5 glazes - and have a glaze break up over the texture - then
using the same body is a no brainer. Everything will fit properly.
Making a dark slip to go on a light body would be the next easiest to do -
start with the same clay and add colour.
Making a white slip to go over a dark body is the hardest of all and needs
some serious testing.
If you are working at cone 6 you already have the tools to get it right in
a fairly painless way - simply test any slips - as you would a clay body
using the fit glazes in chapter 5. If you have tested your clay to find the
relative COE then choose - or adjust the slip that comes closest to the
clay you are using.
Be careful about taking any slip recommended by anyone and assuming it will
work right - every clay body has a different expansion/contraction rate -
and so does every slip - and glaze.
The problem can happen at any temperature but high fire stoneware bodies
can be a big problem - especially if there is any cristobalite in them -
and there is in a lot of them. Put a low expanding slip on a high
cristobalite (high expansion/contraction) body and you have shivering - the
worst possible situation for functional ware.
And don't assume there is no cristobalite in some of the available cone 6
bodies - I have measured a bunch of them now and have found several with
cristobalite - something I thought was impossible at one time.
We have to remember - we here in North America - and probably Europe as
well - have infinite choices of materials - and no tradition to tell us if
any of them work well together - which is why we need to pay attention
more.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
lee love on sun 19 mar 06
--- In clayart@yahoogroups.com, John Britt wrote:
> I am sure that there are many other reasons, that I haven't listed,
> to make up a slip other than your clay body.
John, here are some other aspects we have talked about here
previously.
For the most part, historically, potters tended to prefer clay
that was whiter. They primarily dug their clay right out of the
ground. Folks that used iron bearing clay usually did so, not
because they added iron to the clay body, but because that is what
they had available to them.
It is only since we have been mixing clay with refined industrial
materials, that potters have started putting iron in their clay
bodies. But if you think about it, it makes better sense to apply
an iron bearing slip to a body, rather than putting it in the clay
body. Because, for the most part, what you are trying to do is get
iron interaction with the glaze put over it. By using an iron slip
instead of putting iron in the body, you avoid the hazards of black
coring and bloating, especially in large woodfired kilns that are not
computer controlled.
Sometimes the old timers knew better than us modern folks.
--
Lee In Mashiko, Japan
http://mashiko.org
http://seisokuro.blogspot.com/
"I have been impressed with the urgency of doing. Knowing is not
enough; we must apply. Being willing is not enough; we must do."
--Leonardo
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