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copper reds - fast versus slow cooling cycle

updated wed 14 oct 98


Ray Carlton on fri 9 oct 98

hello is one for the glaze experts..

since changing from my 20 year old gas fired d/draft fibre kiln to a new
IFB d/draft I have noticed that the development of the copper reds have
been nowhere near as strong. I have tried various changes in the pattern
and strength of the reduction but nothing seems to increase the depth of
the reds...I am wondering if there is any evidence to suggest that the
slower cooling rate of the IFB kilm 1300-900 in 8 hours [fibre kiln
1300-400 in 8 hours] is allowing the copper to volatise out of the
glaze..Perhaps a lower firng temperature may help..I would be most
interested to hear any comments that anyone may have in this regard

thanks in advance
cheers :) Ray Carlton

17 Reefton Drive McMahons Creek Victoria 3799 Australia

June Perry on sun 11 oct 98

Dear Ray:

You might want to try opening your damper at the end of the firing and letting
it fast cool down to around 1800 degrees or so and then push the damper back
in and let cool normally. I think there was a discussion of this a while
back. You may want to check the archives.

I wrote the information down somewhere, so if no one posts it or if you can't
find it, write me and I'll see if I can dig it up.

Warm regards,

Chris Trabka on mon 12 oct 98


I've fired ^10 copper reds in two different kilns. One a 16 cubic foot
updraft and the other kiln a 50 cubic foot down draft. When I review the
logs it took 9 hours to get to ^10 in the small kiln and 17 hours to get
to ^10 in the larger kiln. The smaller kiln cooled so red heat was no
longer visable in about 8 hours. The larger kiln cools so red heat is no
longer visable in about 15 to 20 hours.

I have found out that I can fire the larger kiln faster, but when I do
the heating is not even (I believe the reduction varies greatly
throughout the kiln-causing the colors not to be consistent). There is
not appreciably more gas used in the longer firing but the color is much

When I did research on copper reds; it appears that the "red" is formed
early in the firing cycle. It seems to be important to have an initial
phase of heavy reduction at about ^06 followed by light reduction
throughout the remainder of the firing. After ^9, the documentation
suggests that a neutral or oxidation firing will enhance the color
development (make the glazes shinier). I have not tried this last part.


Donn Buchfinck on tue 13 oct 98

I think one of the big problems with firing copper reds is that people over
reduce thier kilns driving off all the copper in the glaze.

In undergrad we learned how to get the kiln going and reducing like a frieght
train. black smoke and all, oh was it exciting, and romantic, and very
unhealthfull not to mention wastfull.

Then we had this teacher of ours show us how to use a C02 annalizer to measure
the co2 in the kiln. the kilns did not look like frieght trains anymore, but
the firings were consistent.

And I do know on the kiln he had built for himself, he had an Oxigen probe and
he could fire that kiln three different times, with pots with the same copper
red glaze and fire with three different adjustments using the oxy probe and
get three beautifull but different results. He knew what he was doing. He
knew his kiln.

In a large kiln that hold a lot of ware and shelves and posts HEAT WORK is an
issue. That is when the heat at the high temperature keeps working on the
ware and glazes and then you can get the glaze running off your pots onto the
kiln shelves. I have made this mistake.

I would recomend anyone who is firing a lot of copper reds to either invest in
a c02 annalizer or an oxy probe.

the romanticism of firing is great, but when you have to pay the bills,
consistency counts.

good luck

Donn Buchfinck