Dannon Rhudy on wed 24 jul 02
At 05:50 PM 07/24/2002 -0400, you wrote:
>Does anyone know what causes copper reds to come out more of a blue color
>with only slight red tints? .....
It sounds like you have some amount of cobalt in your glaze,
and the copper is failing to produce red, so the blue shows through.
Many copper red glazes have a bit of cobalt, so that if the glaze
does NOT turn red, it will be blue instead of clear.
regards
Dannon Rhudy
Paul on wed 24 jul 02
Does anyone know what causes copper reds to come out more of a blue color
with only slight red tints? I am using an old glaze i have used a lot but in
a new kiln, and it never came out blue in the old kiln, except for a slight
tints of blue. I know it was on extremely thick, so maybe there was too much
copper for a red; but other than that i am trying to find an explanation or
go back to a different copper red i used at one point. Any ideas?
Paul
Tom Buck on thu 25 jul 02
Gail D:
??Copper oxide produces a blue when Kona F-4 spar is used in place
of Custer spar??? If two astute observers say it happens, then that may
well be the case. But older textbooks suggest that K-spars promote
purplish copper reds whereas Na-spars tend to make the copper red go
orangey. so perhaps Rhodes et al were wrong?
copper oxide will yield a blue colour should the glaze's
composition edge into the "alkaline" region instead of the usual, common
acidic region of alumina and silica. Who among us have tried "Barium Blue"
glaze? or Raku's "Soda Blue"? Both use a copper compound as colourant.
til later. Peace. Tom B.
Tom Buck ) -- primary address.
"alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada
Gary C. Hatcher on thu 25 jul 02
Blue in copper red is often caused by cooling rapidly or oxidation at the
very end of the firing.
I have found it has less to do with the composition of the glaze and more to
do with how the glaze is cooled or soaked at the end of the firing.
gary
Gary C. Hatcher
e-mail: gchfire@pobox.com
http://www.pinemills.com
Gail Dapogny on thu 25 jul 02
>Does anyone know what causes copper reds to come out more of a blue color
>with only slight red tints? .....
Just the other day, I heard JT Abernathy and Diana Pancioli agreeing that
Kona Feldspar (as opposed to Custer) gives copper reds a blueish cast.
----Gail
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
http://www.silverhawk.com/ex99/dapogny (single historical photo - no longer
registered with Silverhawk)
Geoff Walker on fri 26 jul 02
To (didn't catch the original post, sorry ...),
I think you'll find that you have titania as an impurity or an additive.
Most likely in the china clay or feldspar. I assume you don't have titania
(or rutile) in the glaze nor in an underlying slip.
Hope this helps,
Geoff (Walker).
> >Does anyone know what causes copper reds to come out more of a blue color
> >with only slight red tints? .....
>
> Just the other day, I heard JT Abernathy and Diana Pancioli agreeing that
> Kona Feldspar (as opposed to Custer) gives copper reds a blueish cast.
> ----Gail
>
Marianne Lombardo on fri 26 jul 02
This discussion about copper reds with blue, is this referring to reduction
firings, or oxidation?
Marianne Lombardo
Omemee, Ontario, Canada
mlombardo@nexicom.net
Paul Herman on fri 26 jul 02
Greetings all,
I have two copper red glaze that come out a nice purple/red and bright
red on the outside of covered pots (fired with the lid on) but are
invariably blue on the inside of the same pots. I always thought it was
from a less thorough reduction reaching the interior of the piece. If my
reduction was a bit late or weak the blue color shows up on the outside,
but the inside never turns red. Any ideas?
Hardway Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
Evan Clifford on fri 26 jul 02
I have red somewhere that if there is copper or cobalt in the glaze if
the red burns out then those two colors will show through. Some people
even purposely add a small amount of cobalt to the glaze just incase the
red does burn out, the glaze won't turn out clear.
-Evan
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