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cracking cynthia bringle slip

updated mon 13 aug 01

 

Craig Martell on sat 11 aug 01


Hi:

Sounds like the usual shrinkage thing. There are two ways to deal with
this but no one knows either one. Just kidding.

You can use a defflocculant such as Darvan to cut the amount of water added
to make the slip fluid and useable. Less water equals less shrinkage. You
can also calcine some of the slip and line blend it in to the raw slip
until you find a mixture that is problem free.

I mix my decorating slips in about 150 lb batches. I do this in my clay
mixer. When I make trailing slips I use some calcined slip with the raw
slip so I can trail on bone dry ware if I want. I calcine the raw slip
instead of just the clay because it's easier to mix the trailing slips and
I don't have to figure the Loss on Ignition of the kaolin and compensate
the weigth.

You can fire the raw slip to 1500F and then line blend it in with the raw
stuff to about 50% and see which mix gives you the best results.

later, Craig Martell in Oregon

John Weber on sat 11 aug 01


I have a question for all you users of Cynthia Bringle slip. We will use it
as a decorative addition to white stoneware, slip trailed over leather hard
clay. It was working fine but lately has started to crack as soon as it
dries. The formula we use is as follows and shows its cracking before the
bisque, and cracks even more in the bisque. By cracking I mean small cracks
across the line of slip. Of course, I don't have the expansion ratio for my
clay. Any suggestions would be appreciated.
===========================
EPK 20
Ball clay 20
Nepheline syenite 25
Flint 30
Borax 5
Bentonite 4
Zircopax 15
===========================
Na2O 0.68 Al2O3 2.23 SiO2 13.97
K2O 0.18 B2O3 0.30 P2O5 0.00
MgO 0.06 TiO2 0.05
CaO 0.08 Fe2O3 0.04
ZrO2 0.94

Alumina:Silica ratio is 1.00:6.26
Neutral:Acid ratio is 1.00:5.92
Alk:Neut:Acid ratio is 1.00:2.54:15.01
===========================
John Weber
Manakin-Sabot, VA

Ababi on sat 11 aug 01


I tested it once.
For working on bisque, I used calcined kaolin.
I think you should calcin at least part of the clay .
I would add also about 1% CMC, as a glue
Ababi
----- Original Message -----
From: "John Weber"
To:
Sent: Saturday, August 11, 2001 06:33
Subject: Cracking Cynthia Bringle Slip


> I have a question for all you users of Cynthia Bringle slip. We will use
it
> as a decorative addition to white stoneware, slip trailed over leather
hard
> clay. It was working fine but lately has started to crack as soon as it
> dries. The formula we use is as follows and shows its cracking before the
> bisque, and cracks even more in the bisque. By cracking I mean small
cracks
> across the line of slip. Of course, I don't have the expansion ratio for
my
> clay. Any suggestions would be appreciated.
> ===========================
> EPK 20
> Ball clay 20
> Nepheline syenite 25
> Flint 30
> Borax 5
> Bentonite 4
> Zircopax 15
> ===========================
> Na2O 0.68 Al2O3 2.23 SiO2 13.97
> K2O 0.18 B2O3 0.30 P2O5 0.00
> MgO 0.06 TiO2 0.05
> CaO 0.08 Fe2O3 0.04
> ZrO2 0.94
>
> Alumina:Silica ratio is 1.00:6.26
> Neutral:Acid ratio is 1.00:5.92
> Alk:Neut:Acid ratio is 1.00:2.54:15.01
> ===========================
> John Weber
> Manakin-Sabot, VA
>
>
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