David Beumee on wed 12 feb 03
Lisa-
There is an "interface" between clay and
glaze that happens above cone 9 that helps define
the difference between true and not so true
porcelain or stoneware.
Compared to a cone 10 stoneware, a porcelain
clay body contains a relatively higher percentage of
feldspar, meaning that if you were to look at a fired
and broken piece, you may not be able to tell where
the glaze ends and the clay body begins. This gives
true porcelain an important strength (if the glaze is not
crazed) that can't be had at cone 4, or even at cone 8.
True porcelain is actually very close to glass.
Then there is the issue of whiteness as it
pertains to true porcelain. In the past 12 years I have tested
a great many cone 10 porcelain clay body recipes, and it is
very easy to see what kinds of recipes produce a truly white
fired product,and which recipes produce a grey result.
The line between stoneware and porcelain can be subtle,
and the only real difference is that true porcelain fires white
and is translucent where it is thin. The problem of making
a true porcelain workable on the wheel is the reason why
so many grey porcellanous stonewares are called porcelain.
The catch is that true white is unimportant to many, but for
someone who has been using porcelain for over twenty
years, it's easy for me to see the difference in the clarity
of glazes.
David Beumee
Earth Alchemy Pottery
Lafayette,CO
2/12/03 12:21:01 PM, Harrington wrote:
>Could someone please explain to me the difference between "true
>porcelain," which are words I often see in catalogs describing porcelain
>bodies, and non-true porcelain? I have seen porcelains from cone 4 to
>cone 12, with all sorts of descriptions, but what makes one "true" and
>another not?
>
>Thank you!
>Humbly,
>Lisa
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
Harrington on wed 12 feb 03
Could someone please explain to me the difference between "true
porcelain," which are words I often see in catalogs describing porcelain
bodies, and non-true porcelain? I have seen porcelains from cone 4 to
cone 12, with all sorts of descriptions, but what makes one "true" and
another not?
Thank you!
Humbly,
Lisa
David Beumee on thu 13 feb 03
Of course, the pots from both centers were eagerly
sought by the court and equally supported.
It's obvious that the court of appreciation is alive and well !
What an amazing answer Hank. We need to sit down over
a bottle of good wine.
David Beumee
2/13/03 8:53:45 AM, Hank Murrow wrote:
>On Wednesday, February 12, 2003, at 08:25 PM, David Beumee wrote:
>
>> Snip.......Then there is the issue of whiteness as it pertains to true
>> porcelain. snip...The line between stoneware and porcelain can be
>> subtle, and the only real difference is that true porcelain fires
>> white and is translucent where it is thin. snip....The catch is that
>> true white is unimportant to many, but for someone who has been using
>> porcelain for over twenty
>> years, it's easy for me to see the difference in the clarity of glazes.
>>
>Dear David;
>
>I would like to add to your comments about whiteness. The Chinese moved
>their porcelain production south because of Khitan, Tartar, and Mongol
>pressure on the northern kilns )which had been producing white
>porcelains for 300 years) around 1234 ad. Two brothers, Di Di and Ge,
>found deposits of usable material........hydro thermally altered
>rhyolitic dykes. The deposits in Jingdezhen found by Di Di were white
>and translucent, while the deposits discovered by Ge were 'contaminated
>with iron and rutile, rendering the resultant bodies nearly opaque, but
Pots from both kilns are in
>the best collections around the world. The darker ones are not
>stoneware......they are porcelain in every way except whiteness, a
>quality which we westerners seem to prize perhaps too much. certainly
>the glazes are spectacular on both bodies. BTW, The glazes they used
>consisted of around 20% Limestone, and 80% their throwing body...glazed
>green and once-fired.
>
>I hope this helps flesh out the picture.
>
>Hank in Eugene
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
iandol on thu 13 feb 03
Dear Lisa,
If you check back through Clayart archives for three or four years you =
will find three essays I wrote which pretty well define Porcelain. They =
should give you a start in understanding this Regal material.
You might also like to read Nicole Mones, "A Cup of Light"
Best regards,
Ivor Lewis, Redhill, South Australia
Craig Martell on thu 13 feb 03
David said:
>The catch is that true white is unimportant to many, but for
>someone who has been using porcelain for over twenty
>years, it's easy for me to see the difference in the clarity
>of glazes.
Hi:
Quite so, with regard to the above from David Beaumee.
The body that I use is perhaps not a true porcelain. It contains a small
amount of ball clay and two american kaolins. For most of the glazes that
I use it's just great but when it comes to the blue celadons it is just not
quite white enough. The problem with american kaolins and ball clays is
iron and titanium content. For blue celadons the titanium content of the
porcelain needs to be as close to zero as we can get. I've done lots of
tests with different porcelain bodies glazed with blue and green
celadons. The best results have been with grolleg bodies, which are very
low in both iron and titanium.
Another option if your glazes need a "cleaner" clay to make them sing is to
use slips with grolleg or other china clays that are low in offending oxides.
I have some clays coming from Hammill and Gillespie with the idea of making
another body that will enhance the celadons and some of my other
glazes. These are China clays from ECC and some ball clays from
Hymod. We'll see! I will still use the Turner porcelain for most of my
work because it's hell on wheels when it comes to working properties.
regards, Craig Martell Hopewell, Oregon
Hank Murrow on thu 13 feb 03
On Wednesday, February 12, 2003, at 08:25 PM, David Beumee wrote:
> Snip.......Then there is the issue of whiteness as it pertains to true
> porcelain. snip...The line between stoneware and porcelain can be
> subtle, and the only real difference is that true porcelain fires
> white and is translucent where it is thin. snip....The catch is that
> true white is unimportant to many, but for someone who has been using
> porcelain for over twenty
> years, it's easy for me to see the difference in the clarity of glazes.
>
Dear David;
I would like to add to your comments about whiteness. The Chinese moved
their porcelain production south because of Khitan, Tartar, and Mongol
pressure on the northern kilns )which had been producing white
porcelains for 300 years) around 1234 ad. Two brothers, Di Di and Ge,
found deposits of usable material........hydro thermally altered
rhyolitic dykes. The deposits in Jingdezhen found by Di Di were white
and translucent, while the deposits discovered by Ge were 'contaminated
with iron and rutile, rendering the resultant bodies nearly opaque, but
very beautiful. Of course, the pots from both centers were eagerly
sought by the court and equally supported. Pots from both kilns are in
the best collections around the world. The darker ones are not
stoneware......they are porcelain in every way except whiteness, a
quality which we westerners seem to prize perhaps too much. certainly
the glazes are spectacular on both bodies. BTW, The glazes they used
consisted of around 20% Limestone, and 80% their throwing body...glazed
green and once-fired.
I hope this helps flesh out the picture.
Hank in Eugene
Ababi on fri 14 feb 03
I work with true porcelain in ^6
Therefore it might be untrue. Yet this is the best claybody for crystal firing.
On the other hand I work with stoneware that looks like the true porcelain of 25 ball
clay 25 kaolin 25 silica and 25 feldspar, but the supplier calls it stoneware, perhaps
because he put in unplastic porcelain? i do not know, it is hard to use but fires white
and has nice crystals.
There is Val Cushing porcelain for raku. Ivor Lewis wrote that it was not a true
porcelain, He might be right, but it fires white in raku as well as ^6 and higher ( I fire to
1220C in crystal firing it is higher than ^6)
So I would say it must be translucent andwhite!
I looked yesterday in V.C.,'s book he hassuch bodies for low fire, instead of feldspar he
adds a frit.
Please see here:
http://members4.clubphoto.com/ababi306910/894659/
Ababi
---------- Original Message ----------
>Lisa-
> There is an "interface" between clay and
>glaze that happens above cone 9 that helps define
> the difference between true and not so true
>porcelain or stoneware.
> Compared to a cone 10 stoneware, a porcelain
>clay body contains a relatively higher percentage of
>feldspar, meaning that if you were to look at a fired
>and broken piece, you may not be able to tell where
>the glaze ends and the clay body begins. This gives
>true porcelain an important strength (if the glaze is not
>crazed) that can't be had at cone 4, or even at cone 8.
>True porcelain is actually very close to glass.
> Then there is the issue of whiteness as it
>pertains to true porcelain. In the past 12 years I have tested
>a great many cone 10 porcelain clay body recipes, and it is
>very easy to see what kinds of recipes produce a truly white
>fired product,and which recipes produce a grey result.
>The line between stoneware and porcelain can be subtle,
>and the only real difference is that true porcelain fires white
>and is translucent where it is thin. The problem of making
>a true porcelain workable on the wheel is the reason why
> so many grey porcellaneous stonewares are called porcelain.
>The catch is that true white is unimportant to many, but for
>someone who has been using porcelain for over twenty
>years, it's easy for me to see the difference in the clarity
>of glazes.
> David Beumee
> Earth Alchemy Pottery
> Lafayette,CO
Hank Murrow on fri 14 feb 03
On Thursday, February 13, 2003, at 09:35 PM, David Beumee wrote:
> We need to sit down over
> a bottle of good wine.
>
>
> David;
NCECA?
Hank
Ababi on fri 14 feb 03
After the discussion I had with you Ivor- I started to call these almost
porcelain-claybodies:
KAOLAINS!
Ababi
Rick Mahaffey on sat 15 feb 03
Ababi, et al,
Here in the US in the late 30's and 40's (even into teh 50's) many
potters and instructors were trying to learn
as much as possible about different kinds of clay bodies and, of course,
Porcelain was no exception.
Information was spotty and difficult to come by. One of the porcelain
formulas that was developed produced pretty good results.
That formula was:
25 Kaolin (usually EPK kaolin, Edgar Plastic Kaolin to be exact)
25 Ball clay (usually Kentucky old Mine #4)
(Those two provided the clay and enough plasticity to make the
clay workable.)
25 Silica
25 Feldspar
(The feldspar to impart a degree of translucense, and both to
provide the non- plastic material necessary in a clay body)
(This formula makes an excellent slip for coloring and use in
Hakame, or Mishima, or under a raku clear.)
I heard F. Carlton Ball refer to this as a porcelain body that "we came
up with as a basic porcelain body".
Just who the "we" is a mystery, sometimes I thought it was F C and his
students, somtimes I thought it was the ceramic community.
By the way, we were taught that "true Porcelain" had to be fired in
reduction and needed to be Slightly "blue white"
due to the very small amount of iron in the material.
Another By the way, while living in Japan I purchased porcelain that
was Green, Yellow, Mustard yellow, and Light Brown,when wet.
It all fired out white in the electric kilns and oil kilns that we
fired. I don't know what made the wet clay those colors. Go figure.
Rick Mahaffey
Tacoma, Community College
Ps. At a local private school one of the high school students said "I
want to work with that PORK LOIN clay". Cracks me up every time I
think of it.
iandol on sun 16 feb 03
Dear Ababi,
You say<<"After the discussion I had with you Ivor- I started to call =
these almost porcelain-claybodies: KAOLAINS!">>
I think you have coined an evanescent neologism. A moment of true =
creativity.
Best regards,
Ivor.
| |
|
