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aa copper

updated sun 26 mar 06

 

Ivor and Olive Lewis on fri 24 mar 06


I have been following this thread with some interest wondering when =
someone would chime in about getting blue from Copper carbonate at Cone =
10 in a reduction firing and why it is necessary to include Zinc Oxide =
in this recipe.

There have been posts before about the ease with which Zinc Oxide is =
known to be reduced to the highly volatile metal at such temperatures =
when a kiln is reducing. But why should this glaze be Blue and not Red

Can anyone explain please.

Best regards,

Ivor Lewis.
Redhill,
South Australia.


The ^6 oxidation version:
Cornwall Stone 23.0
Whiting 35.0
EPK 23.0
Frit 3134 10.0
Zinc Ox 5.0
100.0

Copper Carb 4.0
Tin Ox 4.0

Hank Murrow on fri 24 mar 06


On Mar 23, 2006, at 4:14 PM, Ivor and Olive Lewis wrote:

> I have been following this thread with some interest wondering when
> someone would chime in about getting blue from Copper carbonate at
> Cone 10 in a reduction firing and why it is necessary to include Zinc
> Oxide in this recipe.
>
> There have been posts before about the ease with which Zinc Oxide is
> known to be reduced to the highly volatile metal at such temperatures
> when a kiln is reducing. But why should this glaze be Blue and not Red
>
> Can anyone explain please.

Dear Ivor;

I have several copper glazes that I fire in both oxidation and
reduction at cone ten. Over the years I have gradually come to believe
that Zinc aids in keeping the copper in an oxidized state, whatever its
volatility might be. In the past, these copper blues and greens would
turn out liver colored sometimes, but since I began soaking in
oxidation around 1900F during the cooling, I get lovely copper blues
and greens despite earlier heavy reduction for the shinos. I have tried
leaving the zinc out of the recipes, but the color is clearer with it
in.....anywhere from 2 to 5%. No, I can't explain this, only note and
report same. Some of these recipes are in Ian Currie's "Revealing
Glazes".

Cheers, Hank
www.murrow.biz/hank

Alex Solla on fri 24 mar 06


Sure thing Ivor,
Having played with this glaze for more than 5 years, here's the lowdown: copper and tin like eachother a lot. They want to be red. Best I can tell you. You also get nice black copper crystals happening in this glaze sometimes. Basically, it is low enough in SiO2 that you get a soft matt, but when it gets hot enough to start getting glassy, you get pink blushes in hot spots. Most of it though sure isnt blue. It is grassy green.

So, since I wanted green, I dropped the tin out completely. Created a very different green. More blue-ish green. So that led to other tests and soon I had more of a blue turquoise color.

As for the Zinc... made it with it, and without. I agree that it really doesnt contribute anything positive to the melt. Might also be contributing negatively the the Cu-Sn red formation... making it more metallic... just a hunch though.

Cheers,
Alex Solla

Cold Springs Studio Pottery
4088 Cold Springs Road
Trumansburg, NY 14886

607-387-4042 voice/fax
info@coldspringsstudio.com
www.coldspringsstudio.com


Ivor and Olive Lewis wrote:

There have been posts before about the ease with which Zinc Oxide is known to be reduced to the highly volatile metal at such temperatures when a kiln is reducing. But why should this glaze be Blue and not Red

Can anyone explain please.

Best regards,

Ivor Lewis.
Redhill,
South Australia.


The ^6 oxidation version:
Cornwall Stone 23.0
Whiting 35.0
EPK 23.0
Frit 3134 10.0
Zinc Ox 5.0
100.0

Copper Carb 4.0
Tin Ox 4.0

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Ivor and Olive Lewis on sat 25 mar 06


Dear Hank Murrow,=20

Thank you for your observations and opinions.

As much as anything it was the idea that Copper would not respond in =
reduction at such a high temperature by producing the typical red =
colouration but gave instead the Blue Green.

You may well be correct about Zinc Oxide acting as a stabiliser if it is =
retained in the melt and not reduced to the metal. The electron =
structure suggests that it will hold tightly on to anything it =
associates with.

Best regards,

Ivor