Paul Gruner on tue 22 jan 08
Yesterday I fired three test bars of my clay body. One was the original
recipe (let's call it ST-1), the second was 2 parts ST-1 and 1 part Redart
(ST-1 dark), third was a blend of those two - effectively 5 parts ST-1 and
1 part Redart (ST-1 tan).
Unfortunately I only fired to cone 5.5 (I was looking at the wrong cone
through the spyhole).
I made bars 5.5 inches long (1 inch wide and .25 inches thick) and fired
them with just the outside edges supported. None of the samples slumped
noticably. None of the samples came out looking 'shiny'.
Absorption (after one hour in boiling water):
ST-1: 4.3%
ST-1 tan: 2.6%
ST-1 dark: 1.5%
Shrinkage:
ST-1: 12.5%
ST-1 tan: 14%
ST-1 dark: 15%
The tan, after firing, was not much darker than 'buff'. The dark wasn't
extremely dark - more of a medium brown. I like the color.
I'm pretty happy, but I think I should test a little more before I start
using this body on 'real' pots. First, I need to make longer and thinner
bars and fire them to cone 7 to _really_ test for slumping. And I'll test
some pieces with standard glazes to check glaze fit.
For reference, here are the recipes and analysis from Insight:
Pauls ST-1
20.00 Hawthorne Bond
32.00 OM-4 Ball Clay
24.00 EP Kaolin
7.00 Nytal Talc
13.00 Silica
4.00 Nepheline Syenite
0.16* CaO
0.64* MgO
0.10* K2O
0.10* Na2O
0.00* P2O5
0.12 TiO2
2.74 Al2O3
10.45 SiO2
0.06 Fe2O3
0.00* MnO
Si:Al: 3.81
SiB:Al: 3.81
Thermal Expansion: 181.08
---------------------------
Pauls ST-1 tan
16.67 Hawthorne Bond
26.67 OM-4 Ball Clay
20.00 EP Kaolin
5.83 Nytal Talc
10.83 Silica
3.33 Nepheline Syenite
16.67 Redart
0.14* CaO
0.60* MgO
0.16* K2O
0.09* Na2O
0.01* P2O5
0.12 TiO2
2.54 Al2O3
10.60 SiO2
0.13 Fe2O3
0.00* MnO
Si:Al: 4.16
SiB:Al: 4.16
Thermal Expansion: 209.83
------------------------
Pauls ST-1 dark
13.33 Hawthorne Bond
21.33 OM-4 Ball Clay
16.00 EP Kaolin
4.67 Nytal Talc
8.67 Silica
2.67 Nepheline Syenite
33.33 Redart
0.12* CaO
0.56* MgO
0.22* K2O
0.09* Na2O
0.01* P2O5
0.13 TiO2
2.35 Al2O3
10.74 SiO2
0.19 Fe2O3
0.00* MnO
Si:Al: 4.57
SiB:Al: 4.57
Thermal Expansion: 238.09
--------------
I'm still thinking about revising my recipe. If I remove the EPK I could
also reduce the silica and some of the fluxes and just have more clay in
my body. I'd add another clay so that I still had four different clays in
my recipe - I'm thinking Goldart. Does Kaolin have any great qualities
that I've overlooked? Is there any reason not to eliminate it? And is
there any problem with using low-fire clays to provide most of the flux,
instead of adding it in the form of feldspars, talc, etc.?
One more question. Iron is a flux in reduction, but does it have no
fluxing effect at all in oxidation? Does that mean that iron-bearing clays
mature faster in reduction environments? I've never seen a clay body that
said, for instance, "fire to cone 8 in oxidation - and to cone 4 in
reduction."
Ron Roy on mon 28 jan 08
Hi Paul,
A couple of things to keep in mind - ideal shrinkage slould be 12 to 13%
from throwing clay - if you add more clay you will get more shrinkage. Some
of the shrinkage is from melting - you can see that in your results your
clays are probably shrinking too much already. Symptomsof high shrinkage
will be - warping, cracking, and sticking to the wheel head when you try to
lift your pots off.
Hand mixed samples (unless blended with excess water) will not melt as well
as machine mixed samples.
Looks like the only body that will do at cone 7 is the ST-1 - be careful -
talc is a strong melter at cone 6 and 7 - very active - measure carefully
and test each batch before making potys with it.
RR
>Yesterday I fired three test bars of my clay body. One was the original
>recipe (let's call it ST-1), the second was 2 parts ST-1 and 1 part Redart
>(ST-1 dark), third was a blend of those two - effectively 5 parts ST-1 and
>1 part Redart (ST-1 tan).
>
>Unfortunately I only fired to cone 5.5 (I was looking at the wrong cone
>through the spyhole).
>
>I made bars 5.5 inches long (1 inch wide and .25 inches thick) and fired
>them with just the outside edges supported. None of the samples slumped
>noticably. None of the samples came out looking 'shiny'.
>
>Absorption (after one hour in boiling water):
>ST-1: 4.3%
>ST-1 tan: 2.6%
>ST-1 dark: 1.5%
>
>Shrinkage:
>ST-1: 12.5%
>ST-1 tan: 14%
>ST-1 dark: 15%
>
>The tan, after firing, was not much darker than 'buff'. The dark wasn't
>extremely dark - more of a medium brown. I like the color.
>
>I'm pretty happy, but I think I should test a little more before I start
>using this body on 'real' pots. First, I need to make longer and thinner
>bars and fire them to cone 7 to _really_ test for slumping. And I'll test
>some pieces with standard glazes to check glaze fit.
>
>For reference, here are the recipes and analysis from Insight:
>
>Pauls ST-1
>
>20.00 Hawthorne Bond
>32.00 OM-4 Ball Clay
>24.00 EP Kaolin
>7.00 Nytal Talc
>13.00 Silica
>4.00 Nepheline Syenite
>
>0.16* CaO
>0.64* MgO
>0.10* K2O
>0.10* Na2O
>0.00* P2O5
>0.12 TiO2
>2.74 Al2O3
>10.45 SiO2
>0.06 Fe2O3
>0.00* MnO
>
>Si:Al: 3.81
>SiB:Al: 3.81
>Thermal Expansion: 181.08
>---------------------------
>
>Pauls ST-1 tan
>
>16.67 Hawthorne Bond
>26.67 OM-4 Ball Clay
>20.00 EP Kaolin
>5.83 Nytal Talc
>10.83 Silica
>3.33 Nepheline Syenite
>16.67 Redart
>
>0.14* CaO
>0.60* MgO
>0.16* K2O
>0.09* Na2O
>0.01* P2O5
>0.12 TiO2
>2.54 Al2O3
>10.60 SiO2
>0.13 Fe2O3
>0.00* MnO
>
>Si:Al: 4.16
>SiB:Al: 4.16
>Thermal Expansion: 209.83
>------------------------
>
>Pauls ST-1 dark
>
>13.33 Hawthorne Bond
>21.33 OM-4 Ball Clay
>16.00 EP Kaolin
>4.67 Nytal Talc
>8.67 Silica
>2.67 Nepheline Syenite
>33.33 Redart
>
>0.12* CaO
>0.56* MgO
>0.22* K2O
>0.09* Na2O
>0.01* P2O5
>0.13 TiO2
>2.35 Al2O3
>10.74 SiO2
>0.19 Fe2O3
>0.00* MnO
>
>Si:Al: 4.57
>SiB:Al: 4.57
>Thermal Expansion: 238.09
>--------------
>
>I'm still thinking about revising my recipe. If I remove the EPK I could
>also reduce the silica and some of the fluxes and just have more clay in
>my body. I'd add another clay so that I still had four different clays in
>my recipe - I'm thinking Goldart. Does Kaolin have any great qualities
>that I've overlooked? Is there any reason not to eliminate it? And is
>there any problem with using low-fire clays to provide most of the flux,
>instead of adding it in the form of feldspars, talc, etc.?
>
>One more question. Iron is a flux in reduction, but does it have no
>fluxing effect at all in oxidation? Does that mean that iron-bearing clays
>mature faster in reduction environments? I've never seen a clay body that
>said, for instance, "fire to cone 8 in oxidation - and to cone 4 in
>reduction."
>
>______________________________________________________________________________
>Clayart members may send postings to: clayart@lsv.ceramics.org
>
>You may look at the archives for the list, post messages, or change your
>subscription settings here: http://www.acers.org/cic/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
| |
|
