Vince Pitelka on tue 10 jun 08
Karin Dancing Dragon wrote:
"They used to use cats for those great reds, a zillion years ago, in
china, right? Discovered by the guy who ultimately bricked himself up
in the kiln to make some nice red pots for the emperor? Isn't that
how the story went?"
Karin -
There's some skepticism as to the validity of the story, but it's always
good in the telling. Supposedly a late Song or early Yuan Dynasty potter
was experimenting with copper additions to glazes, and one particular
kilnload revealed a brilliant red pot. The potter immediately took the pot
and showed it to the Emperor's agents, and they showed it to the Emperor,
who declared that the man would become an imperial potter (a position of
great status and privilege) and would spend his career making nothing but
fine red pots in service to the Emperor.
The potter was delighted, of course, but then he went back to his studio and
said "Okay, now how the f--k did I get that red?" He performed many
experiments in subsequent firings, but was unable to discover how he got the
red, and finally in desperation he threw himself into the firemouth of the
kiln. Some people further embellish the story by saying that the additional
reduction caused by the combustion of his body produced great copper reds in
that kilnload, but that's pretty far-fetched.
Just as a matter of interest, the potters who invented copper red glazes
were up against a significant challenge. As you know, copper reds are
fickle in the best of circumstances, unless you are Tom Coleman firing in a
Geil kiln. The classic copper reds rely on a tiny addition of copper
(usually 1/4 to 1/2 of 1%) in a low-alumina glaze, with just the right
firing schedule and just the right amount of reduction to reduce the copper
to red copper oxide, which coagulates in microscopic colloidal inclusions
suspended in the glaze to produce the visible red color. If you don't reduce
enough, the copper doesn't turn into red copper oxide, and black copper
oxide (which would give green in larger percentages) in such small
percentages just gives you a clear glaze. If you fire too fast or don't
fire hot enough, the copper oxide never coagulates into visible colloidal
inclusions, giving you a clear glaze. If you fire too slow at high
temperatures, the colloidal inclusions of red copper oxide keep joining
together into larger particles which become visible specks of red in a clear
glaze. If you fire too hot, the glaze (being low in alumina) tends to run,
which thins it out, and the red copper volatilizes from the glaze, or else
reoxidizes to black copper, and you get a clear glaze. Reading all this,
you might wonder how we ever get good copper reds, but with a reliable glaze
recipe, a good controllable gas kiln, and consistent firing practices it
isn't really that hard.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
John on wed 11 jun 08
Like Vince says, getting copper reds is really easy. If you are having =
problems I am having a weekend reduction firing workshop at my studio =
western NC, July 11 -13, 2008.
=20
I am firing for copper reds, shinos and blue celadons. You bring the =
bisque and we will glaze and load on Friday, fire Saturday and unload =
Sunday. You will learn about firing, glazing and get some pots all in =
one quick weekend.
=20
Check out the website for more information or call me at 828-688-6615.
=20
Thanks John Britt
www.johnbrittpottery.com
Lee Love on wed 11 jun 08
On Wed, Jun 11, 2008 at 7:50 AM, John wrote:
> Like Vince says, getting copper reds is really easy.
It is way too easy. I have been attempting copper red decoration,
like this favorite Korean Jar I first saw in Chicago in the '80s:
http://www.mingeikan.or.jp/english/html/db_sinsya3.jpg
My underglaze copper decoration has been obliterated by red.
What do you think the Korean potters did to limit the red color?
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"We are such stuff as dreams are made on, and our little life is
rounded with a sleep." --PROSPERO Tempest Shakespeare
John on wed 11 jun 08
Lee,
I have tried that and what I came up with is described on page 94 of my =
book, under Peach Bloom.
I used a celadon and sprayed a mix of 4 parts copper carbonate and 1 =
part tin oxide, mixed with water or some of the glaze, on the celadon =
and then coated it again with the celadon. I think that you could try =
this and rub it in the carved design and then coat it over with celadon. =
The celadon is stiff and doesn't run and holds the fluxing copper and it =
doesn't all turn red.
You could vary it in any number of ways but it should work for you.
Let me know.
Thanks,
John Britt
www.johnbrittpottery.com/wks.htm
http://ncclayclub.blogspot.com/
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