Daniel Sommerfeld on tue 21 aug 07
Please bear with me...
I am looking for some information into the definition and characteristics
of this phenomena:
A piece is glazed on it's inside with a copper glaze. During firing the
copper passes through the body of the piece resulting in blue/green/red
blushes on the outer surface of the clay. It is similar to fuming and I
could speculate that the fumes pass through the clay body, but I am not
certain.
Today I can't remember the term. Transference, diffusion, etc.
Anyway, I haven't come across a description of this in any text that I
can remember and would like to know more about it.
Questions:
1. Name the process
2. Describe the process
Here are my two interests:
1. What will "pass through"? I know copper will, but what about other
metals/ingredients?
2. To what extent does a clay body affect the process? Will a tight body
pass more or less?
I've done a bunch of clay tests and a body that was terribly thixotropic
also has consistantly pulled copper (lots of it) through the body. I'm
curious whether this was the connection. A photo illustrating this is on
my website near the bottom of my "recent work" page showing a grouping of
tumblers. The far right and left pieces came out of the same firing. The
far right tumbler does not have any glaze inside yet it is red throughout.
This is opposite of having a glaze on the inside, but I have examples of
inside glazed pieces that are red on the outside (not posted/photographed
yet)
Hoping for some enlightenment,
Dan Sommerfeld
www.byhand.us
Paul Herman on tue 21 aug 07
Dan,
It looks to me like the copper is volatilizing or "fuming" into the
kiln atmosphere, and getting deposited on the nearby pieces. So I
don't think it's soaking through your clay bodies, but rather being
transported as a vapor. It only takes a tiny amount to make red.
Copper is notorious for vaporizing. In our wood firings, I try to
discourage the other potters from using copper glazes, because they
invariably stain the other work shades of copper red. Yuck, puce!
The other potters love to use an Oribe glaze (5% copper oxide) in the
salt chamber, so I insist we stack it all on the flue side of the
chamber, and the bad vapors don't affect the pieces on the firebox
side. So everyone is fairly happy about that.
good firings,
Paul Herman
Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com
On Aug 21, 2007, at 12:49 PM, Daniel Sommerfeld wrote:
>
> Hoping for some enlightenment,
>
> Dan Sommerfeld
> www.byhand.us
>
Sue Leabu on wed 22 aug 07
Hi Paul,
Actually, Dan had it right. He is referring to what we call "copper
migration" in our Anagama. (Dan fires in the same Anagama that I do.)
We have a hot zone right up front where it the copper is actually coming
through the clay body, (usually a porcelain or a porcelaneous white
stoneware) and depositing on the exterior of the pots. We don't believe
that it's fuming coming from nearby pieces, as a pot exhibiting this can be
surrounded by shino pots with no other copper nearby. We are also not
seeing fuming of copper onto nearby pots. I have also seen this occur on
pots that are down near the main firebox just above the coal bed, and also
on lidded pots with the lid fired on the pot. The one common element in
every pot we have seen this on is that it is glazed on the interior only,
exterior bare, and in a very hot zone (cone 13).
Sue
Mattawan, MI
On Tue, 21 Aug 2007 15:12:22 -0700, Paul Herman wrote:
>Dan,
>
>It looks to me like the copper is volatilizing or "fuming" into the
>kiln atmosphere, and getting deposited on the nearby pieces.
Daniel Sommerfeld on wed 22 aug 07
Paul,
I do agree that copper can fume and deposit onto the pot and others in the
path, but this is not what I see in this case. Another example: I make
bottles. I glaze the inside of the bottle with an oribe glaze and leave
the outside raw, I then place it in an anagama kiln. After firing, the
outside of the piece will have blue/green colorations unique to the flame
path.
Also, the pieces I referenced from my website were not fired in that
order. Before firing I had no idea what to expect. They were lined up
after firing.
I would bet that a cross-draft salt kiln would see more fuming of adjacent
pieces than a downdraft kiln.
Thanks to Sue Leabu who emailed the answer to my first question: At the
KIA's anagama we call it "copper migration".
Remember a bisqued pot will pass water so other molecules will be able to
do the same.
Thanks for your thoughts,
Dan Sommerfeld
www.byhand.us
Paul Herman on wed 22 aug 07
Dan and Sue,
Thanks for the reply. It's a condition I've never heard of before,
and I don't use copper glazes much at all in the wood kiln. I'll keep
an eye on the other potters' stuff next firing and see if there is
any hint of the copper migration conundrum.
best,
Paul Herman
Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com
On Aug 22, 2007, at 9:38 AM, Daniel Sommerfeld wrote:
>
> Thanks to Sue Leabu who emailed the answer to my first question:
> At the
> KIA's anagama we call it "copper migration".
>
> Remember a bisqued pot will pass water so other molecules will be
> able to
> do the same.
>
>
> Thanks for your thoughts,
>
> Dan Sommerfeld
> www.byhand.us
Angela Davis on wed 22 aug 07
Dan, I think you might try a test with one of your bottles with
copper glaze inside and a stopper to seal it off.
If it is the only copper glaze in the kiln and yo get flashing
I would think this would prove the copper filtered through the clay body.
Angela Davis
Who hates it when the nasty copper flashing get all over the
the pretty transparent Raku glazes.
----- Original Message -----
From: "Daniel Sommerfeld"
To:
Sent: Wednesday, August 22, 2007 11:38 AM
Subject: Re: Diffusion through Clay Bodies? What's the right term...
> Paul,
>
> I do agree that copper can fume and deposit onto the pot and others in the
> path, but this is not what I see in this case. Another example: I make
> bottles. I glaze the inside of the bottle with an oribe glaze and leave
> the outside raw, I then place it in an anagama kiln. After firing, the
> outside of the piece will have blue/green colorations unique to the flame
> path.
>
> Also, the pieces I referenced from my website were not fired in that
> order. Before firing I had no idea what to expect. They were lined up
> after firing.
>
> I would bet that a cross-draft salt kiln would see more fuming of adjacent
> pieces than a downdraft kiln.
>
> Thanks to Sue Leabu who emailed the answer to my first question: At the
> KIA's anagama we call it "copper migration".
>
> Remember a bisqued pot will pass water so other molecules will be able to
> do the same.
>
>
> Thanks for your thoughts,
>
> Dan Sommerfeld
> www.byhand.us
>
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Daniel Sommerfeld on thu 23 aug 07
Angela,
Personally, I believe that this migration/diffusion occurs, but capping
the piece is a good idea; and I was thinking the same thing as a proof.
I'd be curious to see other people try this in their salt/soda and wood-
fired kilns. I have not seen it from cone 10 reduction, but I will try
that in a couple weeks with my thixotropic body (I'll have to find the
recipe).
Thanks,
Daniel Sommerfeld
www.byhand.us
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