Paul on mon 13 oct 03
Any tips on how to obtain the very dark, "oxblood" copper red? Getting
copper reds in general is not hard with my kiln and firing schedule of
reducing at heavily ^012, then very gradually opening up the damper at
several intervals throughout the firing with a final period of oxidation as
the last cones are bending. The color ranges from a strawberry red to a
purple red, depending on how hot they get and how thick, but only once in a
while do i get the oxblood, and not often enough to figure it out yet.
The only hint i have received is that there is only one small part of my
kiln, near the flame trench where floor of the (shuttle) kiln meets up with
the inside edge of the kiln, and on one side the seal is not as good as the
other, where the reds are hard to get. But when they do come out, usually on
only part of the pot, they have a darker color. So my only guess is that the
oxblood perhaps needs a lighter reduction and plenty of oxidation later in
the firing? If anyone with experience with this sort of thing can confirm or
refute this, i would really like to hear from them. thanks,
Paul B
Falmouth, KY
David Hendley on mon 13 oct 03
Firing and cooling practices are probably the most important variables
for successful copper reds.
That said, there are significant differences in copper red glaze formulas.
I've done quite a few tests with Herbert Sanders' many copper red
glazes in his book "Glazes for Special Effects". According to his notes,
different glazes produce different shades of red.
My tests confirmed this. There are some recipes that consistently
produce very dark copper reds. In fact, the darkest ones were not to
my liking, and almost resembled the color of an iron red glaze.
I don't know what variables produce the darker colors, or how to tell
by looking at a formula what color a glaze is likely to produce.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> Any tips on how to obtain the very dark, "oxblood" copper red? Getting
> copper reds in general is not hard with my kiln and firing schedule of
> reducing at heavily ^012, then very gradually opening up the damper at
> several intervals throughout the firing with a final period of oxidation
as
> the last cones are bending. The color ranges from a strawberry red to a
> purple red, depending on how hot they get and how thick, but only once in
a
> while do i get the oxblood, and not often enough to figure it out yet.
Michael McDowell on tue 14 oct 03
I would concurr with David Hendley's observation that different
formulas give different shades of red. Although it is also true that
different firing conditions will also produce some variation. This
can make it difficult to claim certain knowledge about these things.
That said, I would suggest looking to adjusting the alumina silica
ratio alter the hue. From my rather sparse testing in this area, I
believe I've found that higher silica to alumina ratios will give
darker reds, finally giving way to purple. Lower alumina silica
ratios seem to go more toward firey orange. There will probably
always be mysteries about this effect. I seem to get the nicest red
right at the margin next to an area that fails to turn at all.
What's that about?
Michael McDowell
Whatcom County, WA
Michael@McDowellPottery.com
http://www.McDowellPottery.com
travis maxwell on tue 14 oct 03
I have been firing cone 6 reduction oxblood/copper reds lately. I like
cone 6 because it is just hot enough to get a good red color. Just for
the spirit of experimentation, I re-fired some copper red pots in an
electric kiln to cone 6 in oxidation that has an hour soak on cool down
around 1900F. They did not turn green like many would assume. They
turned more of a uniform ruby color that I think most people are looking
for. You might give it a shot on a test piece. Who knows, this might be
the key to getting more consistency with copper reds. I just discovered
this, so more testing is required. I did sell all the pots I did this
too last weekend at a show. The ones I only fired once did not sell as
well.
I got the idea when I used a shelf from my gas kiln in my electric. It
had a small drip of red copper red glaze on it. I ran it through about
10 bisque firings and it never re-oxidized. Each time it seemed to get
redder.
Travis Maxwell in Charlotte, NC
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Michael
McDowell
Sent: Tuesday, October 14, 2003 3:20 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: OXBLOOD REDS
I would concurr with David Hendley's observation that different
formulas give different shades of red. Although it is also true that
different firing conditions will also produce some variation. This
Randy McCall on tue 14 oct 03
Travis
Would you like to share your recipe for your cone 6 oxbloods. I'm
interested in trying them in my gas kiln.
----- Original Message -----
From: "travis maxwell"
To:
Sent: Tuesday, October 14, 2003 2:13 PM
Subject: Re: OXBLOOD REDS
> I have been firing cone 6 reduction oxblood/copper reds lately. I like
> cone 6 because it is just hot enough to get a good red color. Just for
> the spirit of experimentation, I re-fired some copper red pots in an
> electric kiln to cone 6 in oxidation that has an hour soak on cool down
> around 1900F. They did not turn green like many would assume. They
> turned more of a uniform ruby color that I think most people are looking
> for. You might give it a shot on a test piece. Who knows, this might be
> the key to getting more consistency with copper reds. I just discovered
> this, so more testing is required. I did sell all the pots I did this
> too last weekend at a show. The ones I only fired once did not sell as
> well.
>
> I got the idea when I used a shelf from my gas kiln in my electric. It
> had a small drip of red copper red glaze on it. I ran it through about
> 10 bisque firings and it never re-oxidized. Each time it seemed to get
> redder.
>
>
> Travis Maxwell in Charlotte, NC
>
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Michael
> McDowell
> Sent: Tuesday, October 14, 2003 3:20 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: OXBLOOD REDS
>
> I would concurr with David Hendley's observation that different
> formulas give different shades of red. Although it is also true that
> different firing conditions will also produce some variation. This
>
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Dan Dermer on wed 15 oct 03
From the cone 10 copper red recipes I've tested, there seems to be a trend
for darker reds (maroon/ruby) to result from formula that use predominantly
potash (custer or G200) feldspars, while more orangey reds result from
formula based on soda feldspars (neph sy and kona).
Here's one recipe that I've found to be a good performer in my firings,
similar to lots of recipes out there:
Gerstley 11.79%
Whiting 13.62%
Custer 13.01%
NephSy 29.20%
EPK 1.70%
Flint 30.68%
total 100.00%
Add
Tin Ox 1.75%
Copper Carb 0.50%
It has both potash and soda feldspars, and the resulting color is more in
the medium candy-apple red category, at least in my firings. It's from a
blending of recipes seen in Ceramics Monthly in an article on David Cuzick's
work a few years back.
As others have mentioned, probably the most important aspect of just getting
a "red" result is the firing schedule. For me, that means early reduction
at 010, with continued medium reduction through the end of the firing (cone
8-9), and a period of oxidation at the very end between cone 9 and 10.
Then, during cooling, relight and hold for 45 min. to an hour at 1875-1900
degrees.
Have fun!
-Dan
http://pages.sbcglobal.net/ddermer
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