Gary Elfring on sat 29 nov 03
From what I have read, you can get copper red in reduction with glazes that
contain less than 5% of copper. I would like to achieve the same
result in raku? Has anyone tried this? I just figured I could start
with a base crakle glaze and try 2% and 4% copper oxide. Any idea if
this might work? I would love to get a red crakle glaze.
--
Best regards,
Gary
Bruce Girrell on mon 1 dec 03
We have gotten true copper red in raku glazes. By "true copper reds" I mean
a glaze that is a transparent ruby color, with transparency being a key
attribute. Having said that, though, I will also add that the copper red did
not exist uniformly and would probably even be considered a minor
constituent of the result. But then again, I was not trying to maximize the
quantity of copper red. I just took it when it occurred.
The glaze that exhibited this effect most often was Tom Buck's Red Lustre #8
(see the DigitalFire web site), which actually has a ton of copper in it. I
did not experiment with modifying the quantity of copper. Certainly, I would
think that less copper would work, as I could also see spherules of metallic
copper embedded in the glaze. We almost always applied the RL8 over a base
coat of white, which was just a clear base with tin oxide added. We held
reducing conditions during the firing (monitored w/ Oxyprobe) and tended to
fire toward the high end of raku temperatures (RL8 just seemed to work
better closer to ^04 than ^06, maybe even hotter). Color development occurs
during cooling. Post fire reduction was minor, otherwise all you get is
metallic copper.
Sorry I can't give you much more than that, but at least I can say that I
know that it's possible.
Bruce "test, test, test" Girrell
Logan Oplinger on wed 3 dec 03
On Sat, 29 Nov 2003 10:44:06 -0600, Gary Elfring wrote:
>From what I have read, you can get copper red in reduction with glazes that
>contain less than 5% of copper. I would like to achieve the same
>result in raku? Has anyone tried this? I just figured I could start
>with a base crakle glaze and try 2% and 4% copper oxide. Any idea if
>this might work? I would love to get a red crakle glaze.
>
>Best regards, Gary
Hello Gary,
It is possible to get a true copper red (blood red) with a Raku glaze. The
method is based on glass formulas that must be "struck" (reheated and held
at a lower temp.) to develop the red color.
As an experiment many years ago I tried this with a recipe based on a
modified glass formula to melt at Raku temperatures. The test pot was
fired in reduction, allowed to cool to somewhere around 400 deg. F., and
reheated to below dull red heat in a small side chamber built off of the
main Raku kiln chamber. The results were "patchy", but the red color did
develop. The glass formula I used as a start was from one of John Conrad's
books on glaze & glass formulas-- either "Ceramic Formulas: The Complete
Compendium" or "Contemporary Ceramics Formulas", by John W. Conrad, Ph.D.
This was before "Copper Red Glazes" by Robert Tichane became available a
few years ago.
If I can find my Raku striking copper red formula, I will pass it along.
Logan Oplinger
Another Tropical Island
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