Hank Murrow on wed 6 dec 06
On Dec 6, 2006, at 2:25 PM, Alex Solla wrote:
>
> As anyone who makes white clays will tell you, you get to make
> choices...
> you can have WHITE, TRANSLUCENCE, or THROWABILITY... you seldom get 2
> out of
> 3.
> So, if you want white, The compromise
> there was to use a kaolin made for casting, which is fairly low in
> plasticity but VERY
> white, usually pretty high in titanium...
The problem with white bodies arrives with the Lust for Translucency.
Titanium is extremely contraindicated if you wish for translucency.
Ditto for iron. The two(especially TiO2) will scatter light and prevent
translucency. The Southern Chinese porcelains used Petuntse, which was
volcanic rhyolite(very low in Ti and Fe) altered by hydrothermal water
and steam which reduced the alkalies to half their original content,
thus creating a material in which the fluxes were present AT THE
MOLECULAR LEVEL. This allowed translucency while also allowing
plasticity. Much confusion has been spread about petuntse, because two
hundred years ago, these Jingdezhen potters began using kaolin to
'enrich' their bodies as the seam of weathered petuntse began to run
out. Now, they are 3/4 mile deep and the petuntse is not weathered at
all, and therefore not plastic........thus the kaolin addition. It
simply is not Song porcelain any longer. It is a kaolin-based porcelain
with the need for feldspar to melt it. And, it is no longer very
plastic. Things are made very thick and then trimmed to make them
light. Even Janet Gleeson's book, "The Arcanum' did not get the history
of Jingdezhen right. I wonder what Ric Swenson hears about this 'on the
ground' in Jingdezhen.
Cheers, Hank
www.murrow.biz/hank
Alex Solla on wed 6 dec 06
Howdy John,
As anyone who makes white clays will tell you, you get to make choices...
you can have WHITE, TRANSLUCENCE, or THROWABILITY... you seldom get 2 out of
3.
Sure, everyone has their mystical clay that is perfect, but it doesnt
travel.
So, if you want white, find a nice tight, white burning kaolin, a whiteish
ball clay,
and do blends with silica and neph sy. See what you can get to fuse. Cone 6
can be
rough on claybodies... there's a eutectic that seems to hit right around
cone 6 which
will push a nice tight porcelain into slumpy glass pretty quick. The
standard approach
to white clays is 50%clay, 50%non-clay. You need the non-clay to make some
glass and to
keep the mix white. If all you want is a white body that isnt terribly
translucent you
can increase the ball clay considerably, as well as add some
bentonite/hectorite/mix.
Some folks I have known really needed the clay to be WHITE! The compromise
there was to
use a kaolin made for casting, which is fairly low in plasticity but VERY
white, usually
pretty high in titanium... and then offset that with some ball clay and
other kaolins.
Fun stuff to play with.
Email me offline if you want more specifics. I have to admit, I toyed with
making
my own body way back when... then I found Tuckers and havent had a bad clay
day since.
They make awesome mud and it simplified my life immeasurably.
cheers,
Alex Solla
Cold Springs Studio Pottery
4088 Cold Springs Road
Trumansburg, NY 14886
www.coldspringsstudio.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of John Rodgers
Sent: Wednesday, December 06, 2006 4:05 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Mel's 4X25 Porcelain Body
On Tuesday Sept 20, 2005 Mr. Mayor posted his 4X25 white porcelain recipe.
25 epk
25 silica
25 feldspar
25 ball clay
+++++
100
That's lbs, volume, per cent - your choice.
Knowing what range the Mayor works in, this is a cone 10 + clay body
for sure.
Any gurus out there have any idea how to get this down to a cone 6 body?
Or is it possible?
I would really like to have a very white porcelain clay body that I can
mix rather than buy ready made.
Thanks,
John Rodgers,
Chelsea, AL
I have the
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Ric Swenson on fri 8 dec 06
The clay here at this time is certainly not very easy to throw thinly. It i=
s maybe TOO plastic...buttery and hard to throw thinnly...as you say....tri=
m to thinness.
=20
I have seen them crushing rock (Feldspathic stone) to add to the natural c=
lay, but have not asked the percentages now used compared to 1000 years ago=
...if anyone knows. The clay pits at Gao Ling (Kaolin) were exhausted many=
, many years ago and the mountain is beautiful....but now devoid of any min=
ed deposits of clay. An empty shell. I visited there this past summer.
=20
I believe, the local clay now comes from neighboring mountains and areas ar=
ound JingDeZhen. I will check out the clay formulations at the Ceramic Res=
earch Institute, (local version of the ACS) near the Campus of JCI. and wit=
h Jin Wen Wei, Grad. school teacher.
=20
More news at 11:00!
=20
Ric
> translucency. The Southern Chinese porcelains used Petuntse, which was> v=
olcanic rhyolite(very low in Ti and Fe) altered by hydrothermal water> and =
steam which reduced the alkalies to half their original content,> thus crea=
ting a material in which the fluxes were present AT THE> MOLECULAR LEVEL. T=
his allowed translucency while also allowing> plasticity. Much confusion ha=
s been spread about petuntse, because two> hundred years ago, these Jingdez=
hen potters began using kaolin to> 'enrich' their bodies as the seam of wea=
thered petuntse began to run> out. Now, they are 3/4 mile deep and the petu=
ntse is not weathered at> all, and therefore not plastic........thus the ka=
olin addition. It> simply is not Song porcelain any longer. It is a kaolin-=
based porcelain> with the need for feldspar to melt it. And, it is no longe=
r very> plastic. Things are made very thick and then trimmed to make them> =
light. Even Janet Gleeson's book, "The Arcanum' did not get the history> of=
Jingdezhen right. I wonder what Ric Swenson hears about this 'on the> grou=
nd' in Jingdezhen.> > Cheers, Hank
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