David Hendley on thu 15 nov 01
Geez, now I'm up to rule number 8 for firing copper reds:
8. Spray with gold paint and re-fire, or not.
Like Doug, this also does not make sense to me, for the reasons
stated. I have re-fired failed red pieces up to 3 times, never with
any improvement in the amount of red.
I guess it's not as strange as re-firing in an electric kiln to cone 08
to make failed copper reds work.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Doug Gray"
To:
Sent: Thursday, November 15, 2001 10:44 AM
Subject: Horrors of the Un-Red
> With all the discussion about reds, I thought I'd throw this into the
> fray. We have had limited success with re-firing reds that didn't turn
> red during the first firing. As we all know copper is volatile in the
> kiln and can "flash" from one pot to another. With that said, one could
> assume that the amount of copper left in a previously fired, yet un-red
> copper red piece, would be less than the amount that was present in the
> glaze when it was first applied. My experience is that simply re-firing
> the un-red copper red glazes a second time produces and even less red
> un-red, thus supporting the assumption that with each addition firing
> there is less and less copper left in the glaze surface to produce a
> copper red surface.
>
> So, like good little mad scientists, we have been combating the
> diminished copper syndrome (fondly, known as DCS) by adding copper to
> the piece before re-firing. How is this done you might ask? Easy, we
> use gold spray paint. There is no real gold in gold spray paint, at
> least not in the cheap stuff I buy, but there is copper. By spraying
> the un-red pieces "gold" we are actually using the paint to adhere a
> fine layer of copper to the surface of the piece. In the re-fire, the
> copper reds do seem to become more red, thus transporting themselves
> from the realm of the un-red to the realm of the living red.
>
> This is the part of the voodoo that doesn't seem to make much sense to
> me. If copper reds need early reduction to produce the red, then how
> can a vitrified glazed surface and clay body open up again, becoming
> susceptible to the affects of early reduction and the added surface
> copper? And on a related note, is it possible that the burning paint
> itself produces localized reduction on the surface of the piece?
>
> I'm not questioning the process. I've seen it work. I'm just trying to
> understand why it works and what it means to the formation of copper red
> in a reduction atmosphere.
>
> Doug, SC
>
Doug Gray on thu 15 nov 01
With all the discussion about reds, I thought I'd throw this into the
fray. We have had limited success with re-firing reds that didn't turn
red during the first firing. As we all know copper is volatile in the
kiln and can "flash" from one pot to another. With that said, one could
assume that the amount of copper left in a previously fired, yet un-red
copper red piece, would be less than the amount that was present in the
glaze when it was first applied. My experience is that simply re-firing
the un-red copper red glazes a second time produces and even less red
un-red, thus supporting the assumption that with each addition firing
there is less and less copper left in the glaze surface to produce a
copper red surface.
So, like good little mad scientists, we have been combating the
diminished copper syndrome (fondly, known as DCS) by adding copper to
the piece before re-firing. How is this done you might ask? Easy, we
use gold spray paint. There is no real gold in gold spray paint, at
least not in the cheap stuff I buy, but there is copper. By spraying
the un-red pieces "gold" we are actually using the paint to adhere a
fine layer of copper to the surface of the piece. In the re-fire, the
copper reds do seem to become more red, thus transporting themselves
from the realm of the un-red to the realm of the living red.
This is the part of the voodoo that doesn't seem to make much sense to
me. If copper reds need early reduction to produce the red, then how
can a vitrified glazed surface and clay body open up again, becoming
susceptible to the affects of early reduction and the added surface
copper? And on a related note, is it possible that the burning paint
itself produces localized reduction on the surface of the piece?
I'm not questioning the process. I've seen it work. I'm just trying to
understand why it works and what it means to the formation of copper red
in a reduction atmosphere.
Doug, SC
Paul Taylor on mon 19 nov 01
Dear Doug and David and all.
A good experiment to do is to put glazed rings in the kiln and take them
out every hundred degrees centigrade as the kiln cools. Then you will know
exactly what temperature range the red forms and you will be surprised how
low a temperature the red forms. This gives you your striking temperature.
Unless your glaze is totally clear and shiny the glaze can absorb carbon
iron or copper along with tea stains etc
a good idea is to take test rings of all your glazes as they heat up. Put
the rings on a wier with the info from the firing . Doing all this cost you
nothing and you will have gained lots of knowledge from the surprises. You
will now know when to give the pots the most reduction and how they look at
slightly lower temperatures . Remember that a draw trial does not account
for slow cooling so do not panic if the draw trial at the top temp seems so
different - just appreciate the change and the potentials of slow cooling.
-- Regards from Paul Taylor
http://www.anu.ie/westportpottery
I am writing to test my beliefs not to champion them ( I hope)
> From: David Hendley
> Reply-To: Ceramic Arts Discussion List
> Date: Thu, 15 Nov 2001 20:50:05 -0800
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Horrors of the Un-Red
>
> Geez, now I'm up to rule number 8 for firing copper reds:
> 8. Spray with gold paint and re-fire, or not.
>
> Like Doug, this also does not make sense to me, for the reasons
> stated. I have re-fired failed red pieces up to 3 times, never with
> any improvement in the amount of red.
> I guess it's not as strange as re-firing in an electric kiln to cone 08
> to make failed copper reds work.
>
> David Hendley
> Maydelle, Texas
> hendley@tyler.net
> http://www.farmpots.com
>
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