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copper red firing

updated fri 13 jun 08


Linda Arbuckle on sun 23 nov 97


I was also taught that there was a "body" reduction at 06 and a "glaze"
reduction at cone 8-10. Pete Pinnell showed me glaze was reducing at
"body" reduction temperatures. If you miss the low temp reduction,
usually reducing later is not effective. The materials have to be open
and gas-permeable for the reduction to happen. Some high-fire glazes
begin to sinter together much lower than the maturing temperature. The
melted glaze is not gas-permeable. This is why reduced stoneware stays
grey when sealed under a clear glaze, but the exposed clay foot
re-oxizes to that nice toasty orange color.


> I have always understood that 2 different events happen in a reduction
> firing: body red. then glaze red. I am a huge fan of real life as
> opposed to theory, and I believe your results but how does the color
> formation happen below the melting temperatures of the glaze? How is the
> glaze 'starved of oxygen' when it is not hot enough to change it's
> molecular structure?
> Thanks,
> Ron
> Big Baby Head

Linda Arbuckle
Associate Professor, Graduate Coordinator
University of Florida, Box 115801, Gainesville, FL 32611-5801 (Note: this is a new e-mail address)

Wyndham Dennison on thu 12 jun 08

> Date: Wed, 11 Jun 2008 11:15:03 -0700
> From: Karin Givon
> Subject: Cats and Copper Reds
> I gotta reply to vince and his wonderful and intellegent expose of
> how to do the copper red thing--I lived on the Mendocino Coast ( the
> edge of the world) for some 30 years, and had a potter friend who
> worked and worked on getting a good red. At some point, she started
> the reduction at cone 011, reduced it for about half and hour or so,
> then kept the kiln in light reduction for the rest of the fire. She
> now gets good reds every time, and refires many of her pots over and
> over which gives them a look of about four feet deep (welll, I am
> exaggerating, but you know, fabulous depth and movement) and we've
> tried many many recipes, and they all work pretty well with this
> schedule....It is on the coast, so the atmosphere there may affect
> the reduction, but it doesn't seem That Different to fire a kiln on
> the coast ( and I used to fire in Aspen, Colo.) So. Good luck to all
> the red lovers out there.
> And to fire this way wipes out the Kaki of my Texas Red....and works
> well for celedon, of course. Actually, I think that may be how we
> discovered how to do it. I'd love to hear if this schedule works for
> others.
> Karin
> Nevada City, CA
My reduction starts at 015 where I have the six venturi burners paps
open to one turn open and the damper closed to give a wisp of smoke out
the bottom peek of my downdraft. The top reaches reduction first then
the bottom 30 min later. I balance the damper to keep the back pressure
where a lick of flame is coming out the bottom peek. After about 3 hr I
open the PAPS another half turn then as the kiln heats up to cone 6 I
open the PAPS another half turn and open the damper so as to have the
mim back pressure but still some. As my kiln heats it crate it's own
fire storm and the draft starts running hard at about 2000 deg f so I
have to watch and maybe push in the damper to control the ox/reduc
ratio. This may change based on weather and barometric pressure at
different times.
I have an unsubstantiated belief that the reduction back pressure can
be viewed like a soda opened at sea level, some of the bubbles escape
relative to the air pressure at sea level. if you go higher in altitude,
more bubble escape, conversely more pressure less escape. Copper may
well be this way in the kiln, where the reduction also has back pressure
that keeps the copper in the glaze(somewhat) and not volatilizing out in
addition to the reduction to the copper in the glaze.
If I reduce too heavily then I get a muddy liver colored red, but In
this kiln, good bright reds come from a lt to neutral from cone 6 to
cone 10. in about 9-10 hr for a about a 45 cu ft stack
Hope this helps Wyndham