Dave Finkelnburg on thu 3 jun 04
Dear Kat,
I'm not going to touch your question of what porcelain is...too
subjective...but I want to comment on your query about the history of
porcelain.
The story is long so this just skims a few high points. Over 2,000
years ago Chinese potters near Jing De Zhen developed a throwable clay body
from a unique local stone and kaolin. The body was quite plastic, and fired
translucent when thin. It was almost vitrified, apparently around cone 8,
and most importantly, fired very white! That ware was perfected between
2,200 years ago and a thousand years ago or so. Trade secrets seldom stay
secret. The Koreans and Japanese began making their own versions of
porcelain between 900 and 500 years ago.
The Chinese exported a lot of porcelain throughout southeast Asia up
until about the year 1,400 when, culturally, the country turned inward.
However, when Ferdinand Magellan sailed to the far east by going west a
century later, everywhere his expedition went in the Philippines and the
Indonesian archipelago the rich locals at least, however primitive, were
still eating off Chinese porcelain!
Portuguese traders had gotten to the far East well ahead of Magellan and
were bringing porcelain back to Europe. The whiteness of the Chinese
porcelain was so highly prized in Europe it was as valuable as gold!
If you like to read, check out a book called "The Arcanum." It's all
about how a European finally figured out a way to make pottery like Chinese
porcelain, and it's a fantastic read for anyone interested in people and
pottery.
Our "porcelain," by the way, is not the same as Chinese porcelain. We
mix kaolin, feldspar and silica, more or less, and fire it quite high,
sometimes well over cone 10. Our raw materials frequently produce ware that
even when thin is not translucent, probably because it's opaque from
titanium contamination.
Over the centuries local clays in Europe were covered variously with
tin-opacified glazes and later with zinc-opacified glazes to produce a white
background for decorating in the manner of porcelain. The attraction was
the whiteness of Chinese porcelain.
There are many on-line sources of information about porcelain. This
site is one of the better ones.
http://www.artistictile.net/pages/Info/Info_Porcelain.html
Good potting!
Dave Finkelnburg in Idaho
----- Original Message -----
From: "Kat in the Hat"
Sent: Thursday, June 03, 2004 9:15 AM
> For those historical buffs out there. Where does porcelain come from?
China?
> Was the original porcelain bodies made with Kaolin's? Why are porcelains
> perceived to contain so much value?
Kat in the Hat on thu 3 jun 04
What is porcelain? This is a very interesting thread. I was
under the impression that "true" porcelain was a body made up
of primary clays or Kaolin's. Secondary clays, ball clays are
plump full of impurities -- iron oxide, titanium, coal, etc... however
ball clay is more plastic (in general) but dirtier than Kaolin.
White ware or porcelaneous bodies do have ball clay and can be
quite white but are not true porcelains. Nor are all porcelain bodies
translucent, for translucency one needs to use a kaolin low in titanium.
Titanium refracts light and no matter how thin you get your piece it will
not be translucency (same way there is not transparent matte glazes)
Thus that is why Tom Coleman's body is so great or the white Ice (?)
it is because those bodies are translucent and they use grolleg kaolin
or Kaolin very low in titanium. If you mudded up the mix with ball clay,
it would
lose it's entire quality.
Porcelains need to have 0% absorption to be truly vitreous, and transparent
and have that wonder "ring" to it.
For those historical buffs out there. Where does porcelain come from? China?
Was the original porcelain bodies made with Kaolin's? Why are porcelains
perceived to contain so much value?
Kat in the Hat
kat@digitalfire.com
>Is porcelain translucent? Yes if it is made in thin sections but what
>happens if the same formulation is used to make an article say a couple of
>inches think? After firing it certainly will not be translucent.
>Is it vitreous? ... Yes, but what is vitreous? Interpretations vary, from
>zero open porosity to a specified degree of water absorbency, and the
>extent of the latter can vary depending on the test method used.
| |
|
