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copper reds reduced on the way down

updated wed 24 nov 99


David Hendley on thu 18 nov 99

Hmmmmm, I guess I'm a hummingbird, Jeff.

It is pretty well-known, I thought, that copper red
could be achieved by firing in oxidation and then reducing
while the kiln is cooling.
It's called "striking".
I think (but have no first-hand experience) that this technique
is used quite often with glass.

It has been determined that there is a temperature range
of about 200 degrees F when the reduction needs to take
place. Unfortunately, I don't remember the numbers, but
I will look it up for you Jeff, if you no one else supplies the info.

Personally, I've never been too interested in the technique
because I like to fire in reduction for more reasons than
to develop copper reds.
But, with my interest piqued, I have tried striking the kiln
a couple of times, once in the 70's in a gas kiln and a couple of
years ago in my wood kiln.
The first attempt was a total disaster. My copper "red" glaze
turned out dark green. Heavy and opaque, not at all like
a copper red glaze that was simply fired in oxidation.
Worst of all, I caught on fire a roof beam above the back
wall of my kiln because I was injecting gas with the flue
almost completely blocked off. (No real harm - I was on
top of the situation).
Recently I tried striking my wood fired kiln. It was already
fired in reduction, but, hey, if a little reduction is good, a
double dose should be double good. The results:
the copper reds were indeed red, but very muddy and
dark, so much the worse for the double dose. The whole
kiln load had a vaguely lustered look - very subtle, but
noticeable. My high (7%) rutile glaze was actually very
nice, with a slight iridescent look.

I do think this technique could be worth pursuing, but
I won't be the one to do it. I'm already beat after firing
the kiln, so I come in to shower and relax. The thought
of returning for more pyro-fun 6 hours later is not appealing.

David Hendley
Maydelle, Texas

----- Original Message -----
From: Jeff Lawrence
Sent: Monday, November 15, 1999 1:53 PM
Subject: Copper reds - brown-potters please ignore

| ----------------------------Original message----------------------------
| Hello hummingbirds, bulls and other rodophiliacs,
| I had the pleasure of speaking with John Conrad a couple of weeks ago --
| bought some equipment from him (very low prices and interesting tools,
| and couldn't resist bending his ear a little about copper reds.
| This conversation smashed the tablets I've held as gospel.
| According to Tichane, the stage is set for reds on a reduction temp climb,
| but the atmosphere on the way down doesn't really matter. However, JC told
| me about a student of his, Julia Brooks (written up in CM sometime in the
| last few years, but I don't have it) who ox-fired crystalline reds in
| electric kilns to temp, but reduced all the way down. She rigged a slow
| drip off a ceramic probe stuck in the kiln. JC: "She got terrific reds."
| It's hard to reconcile conflicting expert testimony. Does anyone have
| experience with crystalline glazes that shows if they are more open to
| later reduction than amorphous glazes? Since most electric-fired
| crystalline glazes Ive read contain zinc, might there be a post-Hendley
| role for zinc in red formation? Anybody got that CM article handy?
| I don't expect a universal red theory, but I'd enjoy hearing about
| anybody's duplicable experience or even shoot-from-the-hip theories. Yes,
| know I should be testing, but all I've time for is theorizing.
| Jeff

Tom Buck on fri 19 nov 99

David H.
A lady named Mees in Ozland did work on this for her thesis; it
was reported a few years ago in Pottery In Australia if memory serves. Ms.
Mees found that she could get lowfire red from copper if she started
reduction at 800 oC and stopped at 750 oC and then cooled. If she stopped
reducing but heated again when she got to 800 oC the red went back to
green. She also reported that she could cycle back and forth, red or
green, depending on the conditions ( oC, etc.).
I'll cite the reference if you want same.

Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada

hal mc whinnie on fri 19 nov 99

i have fired copper reds in a gas kiln at cone 9-10, upon reaching
temperature I place sticks of wood in the kiln to hold the reduction
during the initial cooling and close the damper and shut down the gas.
i continue for several hours to add sticks of wood.
hal mc whinnie

David W McDonald on sat 20 nov 99

David Henley,
Hi, just read your report on firing copper reds and reducing on
the cool down for the red color. I've been doing this for years now in my
30 cubic foot UPDRAFT kiln, fired with natural gas. I get red everywhere
in the kiln every time! Talked to Pete Pinell once, and he kind of shook
his head and said he didn't really get it, but aknowledged "whatever
works!". I think the thing that stumps me the most is the thought that by
this tempurature the glazes must have cooled to a point where they would
be pretty solid and impervious to atmospheric effects. But evidently not!
I fire to cone ten. Neutral atmosphere to 1880 degrees F. Body
reduction for 30 minutes. Mild reduction to cone 10. Gas off. Damper
closed 30 minutes later. If I have any copper red glazes in the kiln, I
come back 4 to 5 hours later (this is the hard part, cause that usually
means getting out of bed in the middle of the night), when the
tempurature is between 1430 degrees F and 1480 degrees F. I open the
damper about an inch, and turn the burners back on. Heat from kiln
ignites them. I give it just enough gas to bring back pressure down to
the very bottom of the kiln, around the burners. Flames dance and float
lazily around the burner tips. An hour later I turn it off again and
close the damper. That's it.
I've noticed that the reds get smoky and kind of carbon trapped
if I begin this process at a temp lower than the above mentioned, and
kind of irridescent and more elusive at temps higher than 1480 F. But it
works everytime, and we all know how hard it is to say that about copper
reds, especially in an updraft kiln.
The glazes I use are Pete's Cranberrry Red, Orange Red, and the
brightest of all is Rhodes Copper Red.
Any body else tried this?
David McDonald

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Tom Wirt on sat 20 nov 99

Subject: Re: Copper reds reduced on the way down

> ----------------------------Original message----------------------------

I'm not sure if this is going to add anything to the discussion, but I've
found it interesting that when we put Shaner's Oribe over A matte white we
use (Esther's white), we normally get green since we fire a very light
reduction. However, if there is some early reduction by accident, can't
tell you exactly when, and/or moderate reduction higher up in temp, the
stuff can give some fairly interesting reds. We don't seal the kiln very
well cooling since we're not doing heavy reduction, and don't re-reduce

And at times, especially when the glaze has run and caused a foot booger,
we;ll find green outride and red inside the booger. My theory is that early
reduction reddened the inside, and less reduction later left the surface
green. Sometimes this results in a brownish red.

If there's a point to this, some of you might try grinding the surface of
some greens and see what's underneath....or grind some oxbloods and see if
there's green under there, browning things up. Someday we'll find time to
do some controlled tests. Maybe the various glaze formulas make a
difference in their sintering and melt points and how these determine when
reduction can take place and the degree the surface seals itself from
further reduction after melting.

Just observations.

Tom Wirt

Dannon Rhudy on sun 21 nov 99

At 04:52 PM 11/20/1999 EST, you wrote:
>----------------------------Original message----------------------------
>..... read your report on firing copper reds and reducing on
>the cool down .... been doing this for years now in my
>30 cubic foot UPDRAFT .....
...... between 1430 degrees F and 1480 degrees F. I open the
>damper about an inch, and turn the burners back on
....... hour later I turn it off again...... and
>close the everytime.....,...


I've been following (some of ) this most recent thread on copper
reds, and the various means that people use to get consistent ones.
It would appear that there are a number of things that work
well with various kilns. So maybe copper reds are not so tricky
after all.....

The last two firings I did had some reds in them, and I fired as I
usually do, re-lighting the kiln at about 1750F or so, give or take
whatever error in the pyrometer, to slow the cooling.
The reds came out, as usual.
This time, though, I watched them "grow". Pinnell (and others)
have said many times that reds appear in the cooling cycle, so
I deliberately placed a red-glazed bowl right in front of a peep
(Pete's Super Red, once, and a red of my own devising the second time).
When I shut down the kiln, no reds were visible- nor other color
either, too hot to see). As the kiln cooled, I began checking the
peep every thirty minutes. Glaze looked clear on the red bowl,
although by 1900F it was possible to see blues, greens,
browns, inside the kiln. At about 1800F degrees on the pyrometer,
I saw a little spot about as big as a nickel on the side of the bowl,
that was red. The spot "grew" slowly, and by the time the kiln was
at perhaps 1400 degrees - three hours or more - all that I could see
was red, except where the glaze broke white on the edges. It was
most interesting to watch. The red intensified, too, as it cooled.

I get reliable reds in this (downdraft, MFT) kiln most times. The
only exceptions have been when a significant blustery wind has arisen
during the firing (30-40 mph, not unusual here). In those instances,
when I have had red glazes in the kiln, I have gotten - a golden
pink, a sort of "peach bloom", but all over the pots, not just in
spots. A glorious glaze, but I don't think I can rely on the proper
wind speed/direction occuring regularly.


Dannon Rhudy

Bruce Girrell on tue 23 nov 99

Dannon Rhudy wrote:

>This time, though, I watched [the copper reds] "grow".

While we would love to do some high fire experiments, our capabilities for
such work are limited. We concentrate on raku work right now.

Most people don't say the words "copper red" and "raku" in the same
sentence, but if my raku pot is red and I used a copper glaze on it, I don't
know what else to call it. You can see on of these pots on Faye's Clayart

On my monitor the red is a little oranger than on the actual pot. Many of
our pots fall more into the oxblood category, but then, we're using ten
times as much copper as in a high fire copper red.

Anyway, to get to the point of this:
In the raku process, the cooling is done outside the kiln, so you can watch
the whole thing happening right in front of you. It's really fascinating to
watch a basically colorless glaze change to red. There's no question about
when the color is developing. When the kiln goddess is smiling we get them
into the reduction barrel at just the right time to create a thin gold
(copper) iridescence over the red.

Bruce and Lynne Girrell
in Northern Michigan, tired of remodeling and anxious to get back to pots.