Charles Hightower on sat 17 nov 07
I have read that NZ Halloysite has a fine particle size. Just how plastic
is this material? I am planning to sub a portion of EPK in my porcelain to
increase whiteness. I got some from Laguna earlier in the year and have
been itching to use it. The recipe without additives I came up with is as
follows:
UNTESTED cone 10
EPK 45
NZH 10
G200 25
silica 20
Hank Murrow on sun 18 nov 07
On Nov 17, 2007, at 8:33 PM, Charles Hightower wrote:
> I have read that NZ Halloysite has a fine particle size. Just how
> plastic
> is this material? I am planning to sub a portion of EPK in my
> porcelain to
> increase whiteness. I got some from Laguna earlier in the year and
> have
> been itching to use it. The recipe without additives I came up with
> is as
> follows:
> UNTESTED cone 10
> EPK 45
> NZH 10
> G200 25
> silica 20
Dear Charles;
Not very plastic. When dry, the particles tend to roll up into a
tube, creating trimming problems. The transparency is world class.
Doubt any of these observations will be a problem/opportunity at 10%
in your recipe.
Cheers, Hank in Eugene
www.murrow.biz/hank
Daniel Sommerfeld on mon 19 nov 07
I have used the New Zealand Halloysite over the past year in slipcasting.
I can only relate my experiences with it in that capacity.
It is quite white and translucent. It contains very little flux. It is
by far the brittlest casting slip I have tried. It is the spawn of satan.
I have tried a wide range of kaolins in casting: on one end EPK has the
best tooling properties, on the far other end resides NZ which wants to
chip or rip/tear during trimming.
If you are looking for white, but not translucent then try kaopaque which
is one of the whitest opaque kaolins I tried. If you want a kaolin that
has similar whiteness and translucency then try standard or superstandard
porcelains which are much more plastic and friendlier in trimming.
EPK is not very translucent, and 10% NZ won't do much to change that.
I also suggest you consider mixing two separate bodies. One with all EPK
and one all NZ. This way you can mix/wedge sub-batches to test the range
in properties and find a blend that works best.
Good luck,
Dan Sommerfeld
www.byhand.us
Ivor and Olive Lewis on mon 19 nov 07
Dear Charles Hightower,
Some twenty five years ago one of my students brought a clay sample that =
had been retrieved from the basement of his father's sand quarry. Tim =
wished to know if it had any commercial value so I set him to work doing =
some of the standard tests. We discovered that it had an exceptional =
degree of shrinkage form plastic to bone dry and high bisque shrinkage. =
Used alone it was a clay that worked well but suffered from severe "S" =
cracking on drying when thrown. As an additive to reclaimed clay it =
worked well and restored plasticity. It's only other vice was that of =
colour, green when raw, tan when fired. It was my opinion that this was =
an Halloysite type of clay and that crystal morphology was responsible =
for the high linear shrinkage.
For more information about Halloysite clay see
K. Norrish, "An Unusual Fibrous Halloysite" in Clays. Controlling the =
Environment. 10th International Clay Conference. CSIRO. Australia
Kirkman JH. 1981. Morphology and Structure of Halloysite in New Zealand =
Tephras. Clays and Clay Minerals 29:1-9.
Answers.com..Electron microscopy reveals that the morphology of =
halloysite is usually tubular. Because the 1:1 layers in halloysite =
generally are separated from each other by water, halloysite has a =
larger cation exchange capacity, surface area, and catalytic activity =
than does kaolinite.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
David Beumee on mon 19 nov 07
Hello Charles,
NZ haloysite "Ultrafine H" is what I tested from Laguna. Allowing the clay to soak up as much water as possible, then drying it out to a workable consistency, it has only fair plasticity at best. At cone 10 in reduction the test bar I made shrank 19.5%, compared to 20.5% for EPK and similar shrinkage for Helmer kaolin from Idaho.
Ultrafine H is extremely refractory, with a whopping 14.5% absorption at cone 10 in reduction, even with 10% G-200 added. No clay that I have tested fires even close to as white as Ultrafine H, an absolutely put-on-your-dark-glasses blazing white.
You may end up needing 25% spar to properly flux your untested body, but I wouldn't assume you need that much to begin with. Try making up separate body tests with equal amounts of silica and spar, starting with 15% each and moving up 3% for both silica and spar each test, up to 24% each. Let me know what happens please.
David Beumee
www.davidbeumee.com
-------------- Original message ----------------------
From: Charles Hightower
>
> I have read that NZ Halloysite has a fine particle size. Just how plastic
> is this material? I am planning to sub a portion of EPK in my porcelain to
> increase whiteness. I got some from Laguna earlier in the year and have
> been itching to use it. The recipe without additives I came up with is as
> follows:
> UNTESTED cone 10
> EPK 45
> NZH 10
> G200 25
> silica 20
>
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Bruce Girrell on mon 19 nov 07
Charles Hightower wrote:
> > I have read that NZ Halloysite has a fine particle size. Just how
> > plastic is this material?
I find Southern Ice absolutely wonderful to throw. Plasticity-wise, then, I
think it's great. With sharp Bison tools I have no problem trimming, but I
feel that the clay has terrible green strength.
Subbing a portion of Southern Ice - or whatever NZ halloysite you have -
into another batch should improve your translucency to some degree and I
doubt that it would adversely affect your clay body in any significant
manner until it becomes a dominant ingredient and then watch out for the
green strength.
Bruce Girrell
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