John Tiemann on sun 2 feb 03
I am currently using a clay body composed of 50% AP Green to 50% OM-4.
My students are working in both sculptural and thrown forms, so I want
a light (white/off-white) clay body that will hold up well for both
techniques. In order to work with a limited budget at my school I have
replaced AP Green with Hawthorn Bond. I am predominantly firing to ^6
oxidation. Will this substitution be wise, and should the ratio remain
the same 1:1 ?
Am I correct that this clay body will fire well above ^6, therefore,
the clay body will not be completely vitrified? Should I lower the
temp. of the clay body, and how is this possible without changing its color?
(Talc?)
I do have other supplies available (Bentonite, EPK, Talc, etc.). What
can I do to improve my clay body....plasticity, porosity, and
vitrification.... and still keep the lighter color?
As you can see I'm still learning. Thanks for your patience.
John in St. Louis ... saddened over the recent tragedy of the space
shuttle Columbia.
Snail Scott on sun 2 feb 03
At 07:30 AM 2/2/03 -0800, you wrote:
>I am currently using a clay body composed of 50% AP Green to 50% OM-4.
>...In order to work with a limited budget at my school I have
>replaced AP Green with Hawthorn Bond...Will this substitution be wise, and
should the ratio remain
>the same 1:1 ?
I replaced the AP Green fireclay in my regular recipe (30%)
with an equal anount of Hawthorn Bond quite a few years ago.
I didn't notice any particular change in firing temperature.
The plasticity seemed higher, though. And, although I never
noticed it myself, AP Green fireclay had, at least at the
time, a reputation for rather irregular quality control. So,
I didn't mind doing the swap and I think my clay was better
for it. Where I lived, Hawthorn Bond wasn't cheaper, either,
so if it is for you, I can't see a downside at all.
-Snail
David Hendley on sun 2 feb 03
Here are some suggestions for your claybody, assuming you don't
want any radical changes.
AP Green and Hawthorn Bond fire clays are basically the same.
Half fire clay and half ball clay is OK, but OM #4 is not a particularly
light burning ball clay. You would do better with Tennessee #1 or
another white ball clay if you are going for an off-white body.
Starting with 50 pounds each of fire clay and ball clay:
To make the body more vitrified, add at least 12 pounds of feldspar.
You could also add a small amount, like 2 pounds, of talc, but you
want feldspar, not talc, to be the predominate flux.
To insure better glaze fit, add 10 pounds of 200 mesh silica.
For a all-purpose body, you would also do well to add some grog,
on the order of 5 pounds, in the 40 mesh particle size range.
The additions of all these "non-plastics" will decrease your plasticity,
but the body should still be plenty plastic.
The color of the claybody will not be affected much by these additions.
This claybody will probably still not be vitrified, but it will be much
closer than your body of only clay with no additions.
David Hendley
Maydelle, Texas
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> I am currently using a clay body composed of 50% AP Green to 50% OM-4.
> My students are working in both sculptural and thrown forms, so I want
> a light (white/off-white) clay body that will hold up well for both
> techniques. In order to work with a limited budget at my school I have
> replaced AP Green with Hawthorn Bond. I am predominantly firing to ^6
> oxidation. Will this substitution be wise, and should the ratio remain
> the same 1:1 ?
>
> Am I correct that this clay body will fire well above ^6, therefore,
> the clay body will not be completely vitrified? Should I lower the
> temp. of the clay body, and how is this possible without changing its
color?
> (Talc?)
>
> I do have other supplies available (Bentonite, EPK, Talc, etc.). What
> can I do to improve my clay body....plasticity, porosity, and
> vitrification.... and still keep the lighter color?
>
Jim Tabor on mon 3 feb 03
Improving a clay body depends on the body you need. Cardew's remarks
about his experience in Nigeria made the point to the clay's function
and that good English stoneware was not suitable to the local needs.
They began doing export ware for their stoneware. Consider first your
needs. I've been a pots and pans potter working at mostly functional
ware. I started at ^10 and moved to ^6 in mid '70s and to ^1 in '91. I
have learned you can make a good body at these temperatures with a
little testing and an understanding of what you want.
I stopped using free silica in my clay bodies back in the mid '70s and
bring in additional silica from feldspar. I understand the combined
silica (from clays and feldspar) is not as hazardous as free silica.
Clay body dust in the classroom bothers me. I like XX sagger clay (1 of
4 clays) as an addition in the ^1 body I use now and in the ^6 body I
used back when I worked at that temp. I have a good clay body with 60%
clay and 40% non-plastics. Fireclays will be less plastic and more
porous in large additions. I used modest amounts at ^6 and none at ^1.
Drying and fired shrinkage can be adjusted by fine grog or flint along
with the other non-plastics. The coarse additions compared to clay
particles allow more ball clays to create plasticity and fusion (smaller
particles create more surface area to fuse in the melt). Several bars
for each of your test should include bars for a span that will indicate
if it slumps. I also do bars for shrinkage, absorption, and test pots
with a base glaze to see how it fits. On a tour at a Dallas tile plant,
I was told they sent 10,000 tons of a clay from Texas to Italy for
testing it's suitability before they built their factory. Testing
should be a valued part of your experience.
Jim Tabor
David Hendley wrote:
>To insure better glaze fit, add 10 pounds of 200 mesh silica.
>For a all-purpose body, you would also do well to add some grog,
>on the order of 5 pounds, in the 40 mesh particle size range.
>
>The additions of all these "non-plastics" will decrease your plasticity,
>but the body should still be plenty plastic.
>The color of the claybody will not be affected much by these additions.
>This claybody will probably still not be vitrified, but it will be much
>closer than your body of only clay with no additions.
>
>
>
Ron Roy on tue 4 feb 03
Hi John,
I have compared your body to some cone 6 bodies I mind for Tuckers and
Axner - using calculation software - it is way too open at cone 6 - it's
gonna leak.
If you added 10 G200 (or Custer) and 5 Talc you would be pretty close to a
properly vitrified cone 6 body.
As a general rule I won't use more than 30% of any one clay in a body -
cuts down the chances of any one clay that varies from taking the whole
body with it.
I suggest using 25 each of hawthorn 50 mesh and 35 mesh, 25 OM4 is Ok but
here are other ball clays as well perhaps one of the other ball clays that
others have suggested.
Hint - always screen at least the fireclays through 30 mesh - better still
have someone mix this for you - but make sure they screen their dry clays -
get it figured out first - and allow for 1% increased absorption if machine
processed as compared to prepared by hand.
You can always fine tune when you have tested for throwability, shrinkage
and absorbency.
RR
>I am currently using a clay body composed of 50% AP Green to 50% OM-4.
>My students are working in both sculptural and thrown forms, so I want
>a light (white/off-white) clay body that will hold up well for both
>techniques. In order to work with a limited budget at my school I have
>replaced AP Green with Hawthorn Bond. I am predominantly firing to ^6
>oxidation. Will this substitution be wise, and should the ratio remain
>the same 1:1 ?
>
>Am I correct that this clay body will fire well above ^6, therefore,
>the clay body will not be completely vitrified? Should I lower the
>temp. of the clay body, and how is this possible without changing its color?
>(Talc?)
>
>I do have other supplies available (Bentonite, EPK, Talc, etc.). What
>can I do to improve my clay body....plasticity, porosity, and
>vitrification.... and still keep the lighter color?
>
>As you can see I'm still learning. Thanks for your patience.
>
>John in St. Louis ... saddened over the recent tragedy of the space
>shuttle Columbia.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on wed 5 feb 03
I can't see any problem substituting straight across Hawthorn
for AP Green,
What is the rest of the recipe though? No silica or
spar?
David Beumee
2/2/03 4:34:26 PM, Snail Scott wrote:
>At 07:30 AM 2/2/03 -0800, you wrote:
>>I am currently using a clay body composed of 50% AP Green to 50% OM-4.
>>...In order to work with a limited budget at my school I have
>>replaced AP Green with Hawthorn Bond...Will this substitution be wise, and
>should the ratio remain
>>the same 1:1 ?
>
>
>I replaced the AP Green fireclay in my regular recipe (30%)
>with an equal anount of Hawthorn Bond quite a few years ago.
>I didn't notice any particular change in firing temperature.
>The plasticity seemed higher, though. And, although I never
>noticed it myself, AP Green fireclay had, at least at the
>time, a reputation for rather irregular quality control. So,
>I didn't mind doing the swap and I think my clay was better
>for it. Where I lived, Hawthorn Bond wasn't cheaper, either,
>so if it is for you, I can't see a downside at all.
>
> -Snail
>
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