Bryan on thu 21 jul 05
> 1.how much EPK or 6 tile could be subbed for grolleg to cheapen the
body
> without a big loss of workability? too much 6 tile might make the body
> crack more, yes?
>
> 2. if EPK is more plastic and whiter than 6 tile, what good is 6 tile?
it
> flashes well... are there other benefits?
>
In tests this past winter I decided on a 50:50 mix of these two for the
kaolin content of my clay body.
EPK seems grayer and #6 yellower than the blend.
The body with only EPK had a higher shrinkage.
Bryan Johnson
Brian Molanphy on thu 21 jul 05
greetings,
a look at the archive has prompted some questions especially tho not
exclusively for the folks in the subject line (if they still read
clayart).=20
starting with a babu-inspired throwing body=20
grolleg 55=20
custer 17
silica 15
calcined alumina 3
veegum t 2
where the goal is whiteness and resistance to slumping and cracking,=20
1.how much EPK or 6 tile could be subbed for grolleg to cheapen the body
without a big loss of workability? too much 6 tile might make the body
crack more, yes?=20
2. if EPK is more plastic and whiter than 6 tile, what good is 6 tile? =
it
flashes well... are there other benefits?
3. some recipes list calcined alumina and some alumina hydrate... what
difference does calcining make, and should it be calcined to bisc
temperature?
4. can macaloid be subbed for the veegum t? if yes, what percentage?
5. some translucency would be great, but will the alumina eliminate
translucency paritally or completely?
thank you, brian
Antoinette Badenhorst on fri 22 jul 05
Interesting Hank. I did not know that and would like to learn more about
that. How easily can one control throwing big pieces comparing to the =
other
porcelains around?
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
www.clayandcanvas.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Hank Murrow
Sent: Friday, July 22, 2005 1:37 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: porcelain body (martell, deaton, beumee, grimmer)
On Jul 22, 2005, at 6:41 AM, Antoinette Badenhorst wrote:
>
> Of cause one also has to leave the walls as thin as possible to create
> translucency and I am not sure if big pieces will allow that without
> sacrificing technical quality.
Dear Antoinette;
You can achieve translucency up to just shy of 1/2" wall thickness if
you calibrate your body very carefully. The whitest clay and completely
free of titania seems to be the main thing. The halloycitic clays from
New Zealand are the whitest and least contaminated that I have worked
with.
Southern Ice is based upon these clays of volcanic origin. An English
kaolin called Topaz is similarly blessed, but I think Hammil and
Gillespie said it had run out at the mine, or perhaps was not
profitable anymore.
I get translucency to 3/8" from Southern Ice.
Cheers, Hank in Eugene
www.murrow.biz/hank
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pinacoid3000@LYCOS.COM on fri 22 jul 05
Hi Brian
Im sure others will chip in with advice but my comment is just about
translucency. Not only will the alumina impede translucency but so will
using both EPK and No 6 tile., as both have high TiO2 content, an absolute
killer for translucency, with Tile no. 6 in particular being very high
One possible idea is to use another English kaolin. Although Grolleg is
very good if you choose one that is whiter & more plastic you could use
less than the 55% called for in your recipe and then make up with EPK for
price reasons. Also a more plastic kaolin would allow you to drop the
Veegum, which is only there to make it plastic, and is both dirty and
expensive
Regards,
Andy
Antoinette Badenhorst on fri 22 jul 05
Brain I work with a recipe that I brought with me from SA and adjusted here
in the US.
English Grolleg 28kg
EPK 28kg (previously I used Serena kaolin, mined in SA)
Silica (200#) 18kg
P.Feldspar 18kg
Bentonite 1kg (optional,eliminates translucency)
(Sorry for the kg thing....it is easier than lbs.)
Bentonite will make it more plastic, but do nothing for translucency.
You can see some translucent work on my website done with this recipe.
I was recently at a Robin Hopper workshop where he said that he uses silica
#50 (50/50 with silica #200) to allow him to throw bigger pieces. He does
not work with translucency. I am curious about that, but could not find a
place yet that can sell me silica 50#.
Of cause one also has to leave the walls as thin as possible to create
translucency and I am not sure if big pieces will allow that without
sacrificing technical quality.
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
www.clayandcanvas.com
Hank Murrow on fri 22 jul 05
On Jul 22, 2005, at 6:41 AM, Antoinette Badenhorst wrote:
>
> Of cause one also has to leave the walls as thin as possible to create
> translucency and I am not sure if big pieces will allow that without
> sacrificing technical quality.
Dear Antoinette;
You can achieve translucency up to just shy of 1/2" wall thickness if
you calibrate your body very carefully. The whitest clay and completely
free of titania seems to be the main thing. The halloycitic clays from
New Zealand are the whitest and least contaminated that I have worked
with.
Southern Ice is based upon these clays of volcanic origin. An English
kaolin called Topaz is similarly blessed, but I think Hammil and
Gillespie said it had run out at the mine, or perhaps was not
profitable anymore.
I get translucency to 3/8" from Southern Ice.
Cheers, Hank in Eugene
www.murrow.biz/hank
Hank Murrow on sat 23 jul 05
On Jul 22, 2005, at 7:50 PM, Antoinette Badenhorst wrote:
> Interesting Hank. I did not know that and would like to learn more
> about
> that. How easily can one control throwing big pieces comparing to the
> other
> porcelains around?
I have never tried any big wares with these bodies. Don't know how
difficult they would prove.
Cheers, Hank
> www.murrow.biz/hank
pinacoid3000@LYCOS.COM on sat 23 jul 05
Hello Hank,
Yes Topaz is no longer available but the have you tried Super Standard
Porcelain? Also from England it is low in iron, and like all English china
clays it has very low in titania which of course makes it ideal for
translucent porcelain. Its strong and white like the New Zealand china
clays but also is really plastic
Regards
Andy
Craig Martell on sat 23 jul 05
Brian was asking:
1.how much EPK or 6 tile could be subbed for grolleg to cheapen the body
>without a big loss of workability? too much 6 tile might make the body
>crack more, yes?
Hello Brian:
It would be fine to use some EPK but you might want to avoid the 6
Tile. Another poster said that they are both "high" in titanium but that's
not quite accurate. 6 Tile has about 1.5% and that is high but EPK has
0.3% which is higher than the English China Clays but not too bad. You
will have to do some test blends and determine what the best mixture is. I
use a body that has about 15% EPK along with two English China Clays and it
will become translucent. As far as 6 Tile giving the body a penchant for
cracks, I don't think that would happen if you wanted to try some 6
Tile. 6T is a very plastic secondary kaolin and I've used it in some
porcelains without cracking trouble.
>2. if EPK is more plastic and whiter than 6 tile, what good is 6 tile?
Plasticity is a very subjective point. My experience with 6 Tile is that
it's more plastic than EPK and has good green strength. The suitablility
of any clay should be determined by the user and the criteria that the user
has established for his or her needs. What I'm saying is that you find out
"what good is 6 Tile" by testing it.
>3. some recipes list calcined alumina and some alumina hydrate... what
>difference does calcining make, and should it be calcined to bisc
>temperature?
Calcining to Bisque is fine. You start with alumina hydrate and wind up
with alumina oxide after calcining. Try both and see what you prefer. You
can buy a very fine grained alumina oxide from Alcoa. Most suppliers carry
this stuff. If you use about 3% alumina hydrate in a clay or glaze you
will have less alumina oxide in the fired result. Alumina hydrate has some
loss on ignition because of the "hydrate" so factor that in.
>4. can macaloid be subbed for the veegum t? if yes, what percentage?
Yes. Do a direct substitution. 1% for 1%. Another poster says that vee
gum is "dirty". Not true. This stuff is processed twice and fires very
light and clean. You can check it out at RT Vanderbilt's
website. Macaloid is a very white burning plasticizer too. Either one is
very good for a porcelain body. I would recommend using one of these
materials. Your claybody will be a lot more "workable" with an addition of
macaloid or vee gum t.
>5. some translucency would be great, but will the alumina eliminate
>translucency paritally or completely?
Maybe, but the Babu body doesn't have much alumina so it's most likely not
a factor. You'll have to give it a try and see.
I would not use Custer spar for the flux. Try G-200, which has more KNaO
and less silica. I've found that G-200 is a much better feldspar for a
porcelain body. Better vitrification at lower percentages.
regards, Craig Martell Hopewell, Oregon
Hank Murrow on sun 24 jul 05
On Jul 23, 2005, at 10:55 AM, pinacoid3000@LYCOS.COM wrote:
> Hello Hank,
> Yes Topaz is no longer available but the have you tried Super Standard
> Porcelain? Also from England it is low in iron, and like all English
> china
> clays it has very low in titania which of course makes it ideal for
> translucent porcelain. Its strong and white like the New Zealand china
> clays but also is really plastic
Dear Andy, Thanks for the heads up concerning Super Standard........I
will ask Hammil and Gillespie if they carry it here.
Cheers, Hank
www.murrow.biz/hank
pinacoid3000@LYCOS.COM on mon 25 jul 05
Hello Craig,
Thanks for your input but on a couple of points:
Veegum: all the samples I=91ve tested have fired off white, which is much as=
would be expected of smectites. However I know there are quite a few
different grades of Veegum, which one have you found that fires white? The
Vanderbilt website doesn=92t help as chemical analyses are not shown
Titanina: I did note in my initial reply that Tile No.6. had a higher
titania content than EPK. However with the latter having a TiO2 above 0.3%
it is still fair to say this is high. For comparison have a look at all
the English kaolins, and many other kaolisn used in porcelain from Europe
and other parts of the world. TiO2 wants to be minimised as is it
detrimental to both translucency and whiteness
Regards,
Andy
Craig Martell on mon 25 jul 05
Andy responded:
>However I know there are quite a few different grades of Veegum, which one
>have you found that fires white?
Hello Andy:
I haven't found any that will fire white, including macaloid which is made
from hectorite. I use vee gum t and I've also tested vee gum cer. They
fire "off white" but as far as the final result is concerned they're
fine. When you are only using one percent or so in a porcelain body it's
not detrimental at all to use some smectite or hectorite material and it
really improves the working properties of the claybody.
>Titanina: I did note in my initial reply that Tile No.6. had a higher
>titania content than EPK. However with the latter having a TiO2 above 0.3%
>it is still fair to say this is high.
Ok. A lot of this stuff is very subjective and personal preference. If
you think that 0.3% and more is too much titanium I wouldn't argue at
all. To me, it's not, but again, it's a personal take on things.
I agree that the ECC primary kaolins are almost deviod of TiO2 and iron as
compared to US kaolins. The main body that I use now is a mix of Super
Standard, Standard, and EPK. It's very white and develops translucency at
cone 10R. I really don't care if my clay is translucent or not but for the
sake of the green and blue celadons that I sometimes use it's good that the
body is white and as low in TiO2 as I can get it. I like the body to be
fairly pleasant to work with so I'm willing to accept more titanium for
better working properties. That's always the tricky part with porcelain,
trading this for that to get a body that's acceptable.
later on, Craig Martell Hopewell, Oregon
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