Fara Shimbo on thu 17 jun 04
Well, I guess it's SORT OF raku and this is how I do it, anyway.
Fire your favorite Raku producing glaze in your favorite way.
I fire crystalline glazes with about 6% by addition red copper
oxide and 2% by addition silver (washed out from Art Clay Silver)
in a regular oxidation crystal fire. (I see no reason why it
shouldn't work with any glaze.) I fire my stuff to about cone
8.5, hold until I've got as big a crystal as I want and allow to
cool.
When the piece is cool, I set it on a bat on the wheel and
get the wheel turning at its very slowest speed. Fire up the
propane torch and then, holding the torch nozzle about 12 cm
away from the piece (or more, more is better so long as the flame
is touching the piece), I move the torch in slow circles. The
whole idea is never to let the flame linger too long in one spot.
With the copper, you will initially see metallic copper. If you
move the flame away at this point, the copper color remains.
Actually, what you've done is reduce the copper oxide CuO to a
thin film of metallic copper. The longer you heat it, the more
likely the copper is re-oxidize back to CuO. Re-heating just a
little gets you some red. More heat goes to orange, to yellow,
seems to pretty much pass green, then to turquoise, then to royal
blue. You can sometimes, if you keep heating enough, get a
purple, but once you get the blue, you've gone as far as you can
go. Any more and you're back to black and this time it stays.
Now, you won't see these colors develop under the flame.
The area under the flame will always be copper. The colors
"bloom" when the flame is taken away. It's quite a spectacle
to watch! When I teach this technique at workshops everyone
gets so deliciously wide-eyed.
The colors do fade a bit over several months, just as regular
raku does.
I don't have to remind you that these pieces are HOT after
you "light them up." They should be left on the wheel to cool
or moved to a fireproof surface while wearing kiln gloves.
What you get out of all this is a very "velvety" texture. I've
found that if you polish the cooled-down stuff with whatever
copper or silver polish you like, you get the colors where you
left them on a glossy ground; it looks almost like luster...
in fact, I would say this is what the mother-of-pearl luster
-should- look like. The colors are more muted this way but
very lovely. I'm not sure which I like best.
Now, is there anyone out there who can explain to me why I
can't get a true green from this method?
Fa
--
=============================================================
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=============================================================
| |
|
