Ruth Ballou on wed 13 feb 02
I find that it works for slip trailing.
Ruth Ballou
Silver Spring, MD
>> I am going to try this on my own, but wonder if anyone else has had the
>same
>> thought, or already worked it out-----slip made with water that has Darvan
>> (defloc liquid) in it SHOULD have less shrinkage than slip made with just
>> water, right?
>
>Dai -
>I'm not going to say outright that it WON'T work, but I have had dismal luck
>with any attempts to use deflocculated slip for decorating. The reason is
>simply explained. In a deflocculated slip, the particles repel one another.
>As a result, even though there is less water content, the slip flows TOO
>READILY. It won't stay in place on the side of a pot. And if you apply two
>deflocculated slips adjacent to one another, as for marbling or
>feather-combing, they spontaneously begin to intermix along the contact
>line, creating a muddy, unpleasant effect.
>
>Even if you just paint a deflocculated slip on the side of a pot with a
>hakeme brush it doesn't want to stay in place. It just sags. A flocculated
>slip stays where you put it, and adjacent liquid slips do not spontaneously
>intermix. They wait for you to manipulate them.
>
>So from my experience it doesn't work, but I have never tried adding
>glycerin or CMC gum to a deflocculated slip, and that might be worth trying.
>The long chain-like molecules might restore the viscosity.
>
>Rather than trying to use a slip which has less water in it, I suggest
>substituting a little calcined kaolin (or calcine your own claybody) to
>reduce drying shrinkage, and 5% borax to improve adhesion through the bisque
>firing and the early stages of the glaze firing. If you check in Rhodes's
>"Clay and Glazes for the Potter", the most famous old tried-and-true clay
>text, he provides a chart of slip and engobe recipes for application to wet,
>dry, and bisque-fired clays at lowfire, midrange, and highfire temperatures.
>All of them contain 5% borax.
>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/
>
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vince pitelka on wed 13 feb 02
> I am going to try this on my own, but wonder if anyone else has had the
same
> thought, or already worked it out-----slip made with water that has Darvan
> (defloc liquid) in it SHOULD have less shrinkage than slip made with just
> water, right?
Dai -
I'm not going to say outright that it WON'T work, but I have had dismal luck
with any attempts to use deflocculated slip for decorating. The reason is
simply explained. In a deflocculated slip, the particles repel one another.
As a result, even though there is less water content, the slip flows TOO
READILY. It won't stay in place on the side of a pot. And if you apply two
deflocculated slips adjacent to one another, as for marbling or
feather-combing, they spontaneously begin to intermix along the contact
line, creating a muddy, unpleasant effect.
Even if you just paint a deflocculated slip on the side of a pot with a
hakeme brush it doesn't want to stay in place. It just sags. A flocculated
slip stays where you put it, and adjacent liquid slips do not spontaneously
intermix. They wait for you to manipulate them.
So from my experience it doesn't work, but I have never tried adding
glycerin or CMC gum to a deflocculated slip, and that might be worth trying.
The long chain-like molecules might restore the viscosity.
Rather than trying to use a slip which has less water in it, I suggest
substituting a little calcined kaolin (or calcine your own claybody) to
reduce drying shrinkage, and 5% borax to improve adhesion through the bisque
firing and the early stages of the glaze firing. If you check in Rhodes's
"Clay and Glazes for the Potter", the most famous old tried-and-true clay
text, he provides a chart of slip and engobe recipes for application to wet,
dry, and bisque-fired clays at lowfire, midrange, and highfire temperatures.
All of them contain 5% borax.
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/
Ron Roy on thu 14 feb 02
Now I have been slip trailing on my pots for over 20 years now - and I
don't have that problem with deflocced slip. I do use it fairly thick but I
don't think that is the reason it stays put.
Perhaps it is the degree of deflocculation - like not too much. Or maybe
it's because I use throwing slip to start with.
Come to think of it I know other potters who use deflocced slip and they
don't have the problem Vince is talking about.
Trouble with adding calcined clay is you run the risk of upsetting the fit
balence between clay, slip and glaze.
One of the reasons for using Darvan 7 - is you have more latitude - if you
get more in than you need it will still work. This is not true with soda
ash and sodium silicate.
RR
>So from my experience it doesn't work, but I have never tried adding
>glycerin or CMC gum to a deflocculated slip, and that might be worth trying.
>The long chain-like molecules might restore the viscosity.
>
>Rather than trying to use a slip which has less water in it, I suggest
>substituting a little calcined kaolin (or calcine your own claybody) to
>reduce drying shrinkage, and 5% borax to improve adhesion through the bisque
>firing and the early stages of the glaze firing. If you check in Rhodes's
>"Clay and Glazes for the Potter", the most famous old tried-and-true clay
>text, he provides a chart of slip and engobe recipes for application to wet,
>dry, and bisque-fired clays at lowfire, midrange, and highfire temperatures.
>All of them contain 5% borax.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Richard Aerni on thu 14 feb 02
Let me chime in and say that I second Vince's experiences with the use of
deflocculated slip for decoration. I use slip for slip trailing, and in the
past have used quite a bit of brush on/pour on/slop on slip in an attempt to
obtain luscious THICK non-cracking, non-peeling surfaces. My attempts with
Darvan were extremely unsuccessful, probably for the reasons Vince
elucidated in his earlier post (nice explanation Vince!). I too thought
that the reduced water content would enable thicker application...not so.
Well, maybe so, but without the Darvan.
Here is what I do to get a thick ropey slip that shrinks little but sticks
much. First, you must plan in advance, and mix in advance. I make up my
slips months, if not years, ahead of time. Mixing them in a relatively wet
state (200 gm dry slip mix to 1 cup water), sieving through a 100 mesh
screen after a couple of days of wetting, I then set them aside in tight
buckets for a long period of time. Occasionally, I will check them and
decant excess water as the slip settles. After time passes, and it will be
months, not days or weeks, the slip seems to have aged properly, and takes
on a cohesive, ropey quality. I find that prior to this point, if I attempt
to slip trail it, it will come out flat, and be more two dimensional. After
sufficient aging, the slip hangs together and trails out in a raised bead
which is able to withstand a cone 10 firing (at least) without popping or
slumping. I mix slip up in 5 gallon quantities, and make a new bucket every
year. Currently I've got five buckets processing, from each of the past
five years. Over the years I've tried a variety of slip recipes, and found
I can get them all (at least the ones I've tried) to acquire these
properties.
Why does the slip do this? I can't say for certain, not having examined the
results in a scientific manner and on a microscopic level. I'd be curious
if any of the science-type potters would care to weigh in on the matter. I
have speculated that it may have to do with small atomic/molecular charges
causing the particles to bind together moreso than the ordinary plasticity
of the clay platelets (I think these were called Van der Waal's forces if I
remember my chem correctly, but I am really taking a giant leap in the dark
in putting this forward as a possible explanation.). Hamer, in _The
Potter's Dictionary_, (somewhere, I can't find the exact page now) says that
slips will hold together better if aged because of the breaking down of the
clay platelets over time as the slip ages wet. I can't say what the exact
explanation is, only that it is a phenomenon which occurs, and is useful to
me.
Hope this helps,
Richard Aerni
Bloomfield, NY
----- Original Message -----
-----slip made with water that has Darvan
> > (defloc liquid) in it SHOULD have less shrinkage than slip made with
just
> > water, right?
>
> Dai -
> I'm not going to say outright that it WON'T work, but I have had dismal
luck
> with any attempts to use deflocculated slip for decorating. The reason is
> simply explained. In a deflocculated slip, the particles repel one
another.
> As a result, even though there is less water content, the slip flows TOO
> READILY.
Susan on thu 14 feb 02
I have a different method which works for me. One of my ceramic teachers
told me of this method...and so far it works fine...the slip never flakes
off and I apply it thick (1/4+ inch thick).
I use a kitchen blender. I add whatever wet clay the clay body (no grog) of
my pot is made of. I fill the blender 2/3 with wet clay, I add a half a
laundry scoop (not scientific) of Kentucky Ball Clay OM4. To this I add a
little water, a little at a time and add Calgon powder water softener. I add
only a very small "pinch" of Calgon powder to the water--guessing that it
would be 1/4 of 1%. I mix (in the blender) and add enough water, a little at
a time to get a paste consistency--like cake frosting thickness. I store
this clay paste in a plastic jar for a week. I then fill this paste into a
cake decorating (frosting) kit--decorating tip and pouch that I get at a
kitchen dept of a local dept store. I apply this to my WET, not leather hard
pot. I like to decorate my pots with at least 1/4th inch spikes using the
cake decorating tip and pouch as my trailing. My teacher told me it won't
flake off in bisque if you apply to wet clay.
I've brushed on this thick paste for sgraffito design usage.
I have also used the "Air Pen" for slipping for more delicate work but need
to screen first.
I've also done a "no no" by mixing Tom Coleman porcelain cone 10 clay with
just a small pinch of calgon powder and water (no ballclay) and applied it
to my darker stoneware clay surfaces. This way I get a very "white" surface
using stoneware. It has never flaked off. I have been lucky because I am
guessing the shrinkage is different between cone 10 Tom Coleman porcelain
and my cone ten stoneware. I had no problems with crazing using the
following clear glaze but did have crazing problems using other glazes I
tested. You should test your glazes to this slip paste to assure no crazing
will occur.
glossy clear cone 10 glaze:
whiting 19.5
silica 32.9
epk 19.9
custer feldspar 29.5
I am only a student but this method has worked for 1 1/2 years without
failure. I've made many pots with a cactus spike look.
Susan
John Jensen on thu 14 feb 02
In making my slip I used to use a combination of Sodium Silicate and Soda
ash, whick worked well enough. At one point I decided to use Darvan and was
at first surprised at what a weak "effect" I was getting from it. So I
added just a dash of sodium silicate and my blend went all liquid in a
flash. Since then I use a blend of the two.
What does it all mean. I dunno.
John Jensen mudbug@toad.net
iandol on thu 14 feb 02
I would like to follow up on what Vince has been saying.
Before you can discuss Deflocculated slip and how it will behave, =
comments must be qualified with some statements about the volumes or =
weights of water and clay,and also the weights of deflocculants which =
are added, which contribute to this fluid.
It is possible for deflocculated slip to have viscosities which vary =
between that of alcohol and that of thickened cream. Those with a low =
viscosity will flow and also start to deflocculate the clay surface on =
which they are piped or painted, which accounts for the behaviour Vince =
describes. This is because of the large volume of water to clay in the =
fluid and the electron intensity of the deflocculator
But if a defloc slip is allowed to air thicken by evaporation which, =
increases the viscosity, the electronic forces which exist in all wet =
clay substances seem to neutralise the deflocculating function. When =
such a clay slip is brought into contact with a plastic (flocked) clay =
body the slip will set up almost immediately, almost like super-glue.
This, I imagine, would give a clue as to the nature of the best slip to =
select for slip trailing.
Best regards,
Ivor Lewis. Redhill, South Australia
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