Robert Harris on mon 21 may 12
To summarise Robert Tichaen's work on this subject:
He gives very convincing evidence that copper red is due to colloidal
copper metal in a sandwich layer between two clear layers of glaze.
The red colour is due to the size of the colloid particles and the
fact that their size means they reflect only red light - in much the
same way as the sky is blue.
Copper reduction occurs early and before the glaze has sealed over. In
fact he shows a very convincing red and green glaze test where the
green glaze has the same recipe as the red glaze, but with 20% more
frit added. He surmises that the green glaze melts before the red
glaze (and reduction takes place). It was only reduced for a small
amount of time, the rest of the firing being in oxidising conditions
(after the red glaze has formed and sealed over itself).
The reason that reds "appear" during cooling, is that this is when the
copper atoms start to aggregate. Fast quenching of hot copper red
glazes will give clear glazes, but with suspended copper particles of
<1mm diameter, but observable with a hand lens. If they are cooled
more slowly a colloidal suspension with particles in the 20-200
Angstrom range are seen (just for reference the atomic radius of the
copper atom is about 1.3 Angstroms - 130pm). Actually in one chapter
of the book he says that he thinks that at this point the copper
particles may be re-oxidised to cuprous oxide, but since this
contradicts most of the rest of the book, I'm ignoring it.
He states that by 500C (932F) copper nucleation has occurred and
cooling may be sped up. He also shows that if a quenched copper red is
reheated to between 600-800C it will return to its red colour.
So in conclusion the necessary reduction of copper is formed in the
early part of the firing, and if this does not happen you will never
get a copper red, but the red colour itself is "developed" at around
600-800C.
However, I suspect that if you open the kiln after the 450F burning
paper test, you are not going to affect your copper reds.
As to them getting deeper over time, at room temperature, I am
somewhat sceptical, although it is possible that the colloidal
particles continue to condense a little, which in some glazes may
intensify the colour one way or another.
Robert
On Sun, May 20, 2012 at 4:01 PM, Jeff wrote:
> Hi
> Just wanted to stick a contrarian oar in the stream of assertions that th=
=3D
ere's no changes in glazes after kiln is cooled to X degrees,
> For one thing it's always risky to make universal proclamations since you=
=3D
d have to test the whole universe of possible firings and glazes to be sure=
=3D
.
> As for me, I'm going to look for another microscope to borrow to examine =
=3D
my cu reds. Last time I was working on them I intrigued a brilliant friend =
=3D
into using his and it looked under the scope as tho the color deepened at a=
=3D
mbient temp over the first month after unloading.
> Window glass will sag and devitrify over time - why should our weirdly fo=
=3D
rmulated glasses be more stable? Just say no to universal negatives!
> Trenchantly yours
> Jeff
--=3D20
----------------------------------------------------------
John Britt on mon 21 may 12
I am all for contrarians, but I said:
"Ok.....An average glaze set temperature is around 1300 F . That means=3D20=
=3D
it usually doesn't change after that no matter what you do."
Tried to include the words "average" and "usually" to cover that.
I know that Raku will change, especially after sitting in the Texas sun f=
=3D
or=3D20
three months but that is surface oxidation.
John Britt Pottery
Jeff Lawrence on mon 21 may 12
Hi,
I think Tichane's the man, too, Richard, and the success people have had
with good color from pre-sealing reduction and firing down/refiring to
mimic ruby glass "striking" seems to confirm a lot of the stuff that was
novel when he wrote that book. But the cu red is actually ancillary to my
main musing, which is this: Has anyone else has had the bizarre experience
of seeing color formation or any other changes besides crazing/shivering at
ambient temps? I'd doubt my own experience except that my late
co-conspirator was a fairly renowned scientist not given to unfounded
claims.
In several samples we examined the day after unloading, the red coloration
we saw looked like wisps of ruby smoke - very surreal in the microscope,
like an alternate universe in a comic-book. A month later, he was looking
at the same samples and called me up to come check them out, because the
wisps seemed longer, thicker, and redder. The images Ray made are long gone
with the rest of his estate. Glazes seem pretty set in their habits to me,
too, and I seldom see them flow off room-temp pots, but those tests make me
wonder about the limits of their setting.
Jeff
in New Mexico, which I'd like to make clear is NOT in Texas
Lee on mon 21 may 12
On Mon, May 21, 2012 at 10:51 AM, Robert Harris w=
=3D
rote:
> To summarise Robert Tichaen's work on this subject:
>
> He gives very convincing evidence that copper red is due to colloidal
> copper metal in a sandwich layer between two clear layers of glaze.
My teacher, Tatzuso Shimaoka did his copper reds by putting down a
layer of clear glaze, then a layer of copper slip and then a layer of
clear. I like it because sometimes, when the clear layers are thin,
the copper breaks metallic.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Lee on mon 21 may 12
On Mon, May 21, 2012 at 2:03 PM, Johanna San Inocencio
wrote:
> what cone would this be fired to?
> Johanna
9/10, in the reduction chamber. You have to have the right clear
glaze. Try a copper red without copper.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Johanna San Inocencio on mon 21 may 12
what cone would this be fired to?
Johanna
On May 21, 2012, at 11:48 AM, Lee wrote:
> On Mon, May 21, 2012 at 10:51 AM, Robert Harris =3D
wrote:
>> To summarise Robert Tichaen's work on this subject:
>>=3D20
>> He gives very convincing evidence that copper red is due to colloidal
>> copper metal in a sandwich layer between two clear layers of glaze.
>=3D20
> My teacher, Tatzuso Shimaoka did his copper reds by putting down a
> layer of clear glaze, then a layer of copper slip and then a layer of
> clear. I like it because sometimes, when the clear layers are thin,
> the copper breaks metallic.
> --
> Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>=3D20
> "Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97t=
hat =3D
is, "The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
wynpotter on tue 22 may 12
Harding Black experimented with many varieties of recipes of copper
reds. Most of these were 2 glaze combinations where the first glaze
contained the copper and the second was the same except it had no copper
but the tin. These test worked very well and looked beautiful.
The thought behind this was to protect the copper from inadvertent
oxidation.
I have seen these test tiles and the recipes and can attest to the
vibrancy of the reds. Harding believed that this was the method that the
early Chinese potters used. Harding did not use saggers at the time I
knew him although I have read that saggers were used by the Chinese
potters. I think the difference in fuel, wood vs gas could be a factor
in whether saggers are needed.
I believe Harding's kiln was a hardbrick downdraft that cooled slowly,
Dale Neese might shed some additional thoughts on Harding firings as I
was never around at those times.
Just a few thoughts on the subject.
Wyndham
Robert Harris on tue 22 may 12
Back to Tichane again.
Remember that Cu reds are due to interference by Cu agglomerates at
the wavelength level. Specifically this means that Copper Reds are not
due to absorption of all wavelengths apart from red by a compound
dissolved in the glass/silica matrix, but rather how the size of the
the copper agglomerates interfere with specific wavelengths (the same
reason that the sky is blue).
This means that optical microscopy on the glaze shard will differ
depending on whether reflected or transmitted light is used.
He also suggests that the different hues and shades of red are due to
the amount of copper blue (and other contaminants e.g. carbon)
contaminating the rest of the glaze and therefore changing the
observable colour of the red produced by the copper atom agglomerates.
In addition Tichane makes the point (which is relatively obvious) that
observation of copper reds will differ significantly in sunlight
versus cool white fluorescent light.
He has an entire chapter discussing the physics of light and copper
red glazes, a bit too much to summarise here but ... it's definitely
complicated. If you look at a cross section he states that you can see
the copper layer, and then the degree of contamination of the clear
layer on top will determine a good deal of the hue (especially for the
darker maroons).
Robert
On Tue, May 22, 2012 at 4:22 PM, Taylor Hendrix wro=
=3D
te:
> I'm curious to know what hue, tint, shade, and saturation standards we us=
=3D
e
> for microscopic measuring of our Cu reds.
>
>
> Taylor, in Rockport TX
> wirerabbit1 on Skype (-0600 UTC)
> http://wirerabbit.blogspot.com
> http://wirerabbitpots.blogspot.com
> http://www.flickr.com/photos/wirerabbit/
> https://youtube.com/thewirerabbit
>
>
> On Tue, May 22, 2012 at 1:20 PM, Url Krueger wrote=
=3D
:
>
>> Something to think about is the quality
>> of light used to look at the glaze. =3DA0Early
>>
--=3D20
----------------------------------------------------------
Url Krueger on tue 22 may 12
Something to think about is the quality
of light used to look at the glaze. Early
or late in the day a glaze may be perceived
as being more red than at noon due to the
decrease in strength of the blue wavelengths
at those times. The same may be true using
incandescent vs fluorescent artificial light.
However, if one were looking at a glaze using
a microscope with an understage artificial light
source one would expect the light quality to be
the same for independent observations.
earl in Oregon
Taylor Hendrix on tue 22 may 12
I'm curious to know what hue, tint, shade, and saturation standards we use
for microscopic measuring of our Cu reds.
Taylor, in Rockport TX
wirerabbit1 on Skype (-0600 UTC)
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
https://youtube.com/thewirerabbit
On Tue, May 22, 2012 at 1:20 PM, Url Krueger wrote:
> Something to think about is the quality
> of light used to look at the glaze. Early
>
Jeff Lawrence on wed 23 may 12
On Wed, May 23, 2012 at 8:52 PM, Robert Harris wro=
te:
> Tichane does indeed say that alumina leaching from the claybody
> generates the clear layer underneath the copper.
>
> He actually shows that with a pure silica body there is no clear layer
> underneath (but there is still one on top).
>
> When he talks about a clear underlayer and top layer (with copper
> sandwiched between the two), these layers are all generated, during
> firing, from one thick application of the copper red glaze, so I am
> not sure there is any point in putting an additional underlayer. I'd
> also note that unless it was the same base glaze, it would either be
> underfluxed or overfluxed which might cause additional problems.
>
Time to re-read those Tichane books. A pure silica body is a delightfully
elegant way to show the alumina done it.
I'm mulling layer possibilities to eliminate that dark gray that soils the
rims of white stoneware. Any idea what that is?
Jeff Lawrence
jefflawr@gmail.com
Jeff Lawrence on wed 23 may 12
Hey Lee and Wyndham, thanks for sharing the 'copper in the middle' tales!
Both add to my glaze test to-do basket.
Lee, I remember that under Ray's polarizing microscope, we often saw swarms
of copper beads that looked at high magnification like little asteroids,
but vaguely recall they only showed up in glazes so dark from red
coloration that they were practically black (and too ugly even to be
interesting). I like the idea of copper foil in a clear glaze sandwich.
And Wyndham, I've heard before about Harding Black's insatiable testing. I
think Tichane talked about the alumina from the clay body leaching into the
adjacent glaze layers, changing it so that the color doesn't develop there.
I wonder if Harding Black's first layer provided some kind of barrier to
that party-pooping alumina?
I've been thinking about a multi-layer approach for another problem, too,
which goes to what Earl and Taylor were pondering - color. I dislike that
dirty gray on the edges of white stoneware, that makes copper-reds look
permanently unwashed. But I don't have the mindset to throw porcelain,
which stays white. I also dislike the oversaturated color that reaches at
best a kind of a brown garnet color. It may be the glaze sandwich, with
backlighting refracted through the underlayer, is what gives that
illuminated ruby color? In any case, I'll try what's been suggested as a
first try- same glaze sans copper but with tin.
Jeff
Cwiddershins on wed 23 may 12
Same base. =3D20
--
Lee Love in Minneapolis
http://mingeisota.blogspot.com/
"Ta tIr na n-=3DC3=3DB3g ar chul an tI=3DE2=3D80=3D94tIr dlainn trina ch=
=3DC3=3DA9ile"=3DE2=3D
=3D80=3D94that is, "The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue --sent from my iPod
On May 23, 2012, at 9:43 PM, Robert Harris wrote:
> I'm curious, were the base glazes to which he added the iron and
> cobalt, and then layered the same base, or different bases as well?
>=3D20
>>=3D20
>> Jeff,
>>=3D20
>> Shimaoka used the "sandwich" technique with iron and also gosu
>> (impure cobalt.) These will also break metallic where the top coat
>> is thin. To me, a much more interesting effect that one layer glazes
>> containing these oxided.
>>=3D20
>> One of the creative ways Shimaoka would use this technique is by
>> not putting the oxide in round windows. These would remain a clear
>> window where an overglaze enamel was later placed.
>>=3D20
>> Thanks for helping me think about these things. They are
>> one of the many techniques I was exposed to in Japan, but haven't had
>> the chance to try here.
>>=3D20
>> Except, I have been doing the techique with Mino shino,
>> where you add maybe 5 to 10% RIOx to the glaze, apply it first then
>> cover with the regular Mino Shino. You get consistent reds with
>> this.
>>=3D20
>>=3D20
>> --
>> --
>> Lee Love in Minneapolis
>> http://mingeisota.blogspot.com/
>>=3D20
>> "Ta tIr na n-=3DC3=3DB3g ar chul an tI=3DE2=3D80=3D94tIr dlainn trina c=
h=3DC3=3DA9ile"=3D
=3DE2=3D80=3D94that is, "The
>> land of eternal youth is behind the house, a beautiful land fluent
>> within itself." -- John O'Donohue
>=3D20
>=3D20
>=3D20
> --=3D20
> ----------------------------------------------------------
Robert Harris on wed 23 may 12
Tichane does indeed say that alumina leaching from the claybody
generates the clear layer underneath the copper.
He actually shows that with a pure silica body there is no clear layer
underneath (but there is still one on top).
When he talks about a clear underlayer and top layer (with copper
sandwiched between the two), these layers are all generated, during
firing, from one thick application of the copper red glaze, so I am
not sure there is any point in putting an additional underlayer. I'd
also note that unless it was the same base glaze, it would either be
underfluxed or overfluxed which might cause additional problems.
On Wed, May 23, 2012 at 3:38 AM, Jeff Lawrence wrote:
> Hey Lee and Wyndham, thanks for sharing the 'copper in the middle' tales!
> Both add to my glaze test to-do basket.
> Lee, I remember that under Ray's polarizing microscope, we often saw swar=
=3D
ms
> of copper beads that looked =3DA0at high magnification like little astero=
id=3D
s,
> but vaguely recall they only showed up in glazes so dark from red
> coloration that they were practically black (and too ugly even to be
> interesting). I like the idea of copper foil in a clear glaze sandwich.
> And Wyndham, I've heard before about Harding Black's insatiable testing. =
=3D
I
> think Tichane talked about the alumina from the clay body leaching into t=
=3D
he
> adjacent glaze layers, changing it so that the color doesn't develop ther=
=3D
e.
> I wonder if Harding Black's first layer provided some kind of barrier to
> that party-pooping alumina?
> I've been thinking about a multi-layer approach for another problem, too,
> which goes to what Earl and Taylor were pondering - color. I dislike that
> dirty gray on the edges of white stoneware, that makes copper-reds look
> permanently unwashed. But I don't have the mindset to throw porcelain,
> which stays white. I also dislike the oversaturated color that reaches at
> best a kind of a brown garnet color. It may be the glaze sandwich, with
> backlighting refracted through the underlayer, is what gives that
> illuminated ruby color? In any case, I'll try what's been suggested as a
> first try- same glaze sans copper but with tin.
> Jeff
--=3D20
----------------------------------------------------------
Robert Harris on wed 23 may 12
I'm curious, were the base glazes to which he added the iron and
cobalt, and then layered the same base, or different bases as well?
>
> Jeff,
>
> =3DA0 =3DA0 =3DA0 =3DA0Shimaoka used the "sandwich" technique with iron a=
nd also =3D
gosu
> (impure cobalt.) =3DA0 These will also break metallic where the top coat
> is thin. =3DA0 To me, a much more interesting effect that one layer glaze=
s
> containing these oxided.
>
> =3DA0 =3DA0 =3DA0One of the creative ways Shimaoka would use this techniq=
ue is =3D
by
> not putting the oxide in round windows. =3DA0These would remain a clear
> window where an overglaze enamel was later placed.
>
> =3DA0 =3DA0 =3DA0 =3DA0Thanks for helping me think about these things. =
=3DA0 =3DA0The=3D
y are
> one of the many techniques I was exposed to in Japan, but haven't had
> the chance to try here.
>
> =3DA0 =3DA0 =3DA0 =3DA0 =3DA0Except, =3DA0 I have been doing the techique=
with Mino s=3D
hino,
> where you add maybe 5 to 10% RIOx to the glaze, apply it first then
> cover with the regular Mino Shino. =3DA0 You get consistent reds with
> this.
>
>
> --
> --
> =3DA0Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>
> =3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=
=3D97that is=3D
, "The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
--=3D20
----------------------------------------------------------
Lee on wed 23 may 12
On Wed, May 23, 2012 at 2:38 AM, Jeff Lawrence wrote:
> illuminated ruby color? In any case, I'll try what's been suggested as a
> first try- same glaze sans copper but with tin.
> Jeff
Jeff,
Shimaoka used the "sandwich" technique with iron and also gosu
(impure cobalt.) These will also break metallic where the top coat
is thin. To me, a much more interesting effect that one layer glazes
containing these oxided.
One of the creative ways Shimaoka would use this technique is by
not putting the oxide in round windows. These would remain a clear
window where an overglaze enamel was later placed.
Thanks for helping me think about these things. They are
one of the many techniques I was exposed to in Japan, but haven't had
the chance to try here.
Except, I have been doing the techique with Mino shino,
where you add maybe 5 to 10% RIOx to the glaze, apply it first then
cover with the regular Mino Shino. You get consistent reds with
this.
--=3D20
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Robert Harris on thu 24 may 12
My immediate first guess, especially as it is grey, was reduced iron.
Since a good copper red needs early reduction (before any sort of melt
occurs), the body iron (at the surface anyway), might get reduced with
the copper and then sealed in (along with the copper) when the glaze
melts, protecting it from re-oxidation during cooling. While true
"body reduction" needs very very heavy reduction throughout the firing
cycle, I don't see why just a surface layer might not become grey
enough to look nasty at the top of your copper reds.
Other than Iron I'm struggling to think of a contaminant that is in
stoneware, that isn't in porcelain. Frankly the easiest solution might
just be to slip your pots (maybe even just the tops if it isn't too
noticeable. I'd have thought any porcelain slip would do. The other
possibility would be to use some sort of opacified underlayer -
perhaps the copper base with just enough Zircopax to hide the grey?
The zircopax would make the underlayer more refractory, but you might
be able to adjust it enough so that it plays nicely.
Can't think what else to suggest.
Robert
On Thu, May 24, 2012 at 12:56 AM, Jeff Lawrence wrote:
> On Wed, May 23, 2012 at 8:52 PM, Robert Harris
> wrote:
>>
>> Tichane does indeed say that alumina leaching from the claybody
>> generates the clear layer underneath the copper.
>>
>> He actually shows that with a pure silica body there is no clear layer
>> underneath (but there is still one on top).
>>
>> When he talks about a clear underlayer and top layer (with copper
>> sandwiched between the two), these layers are all generated, during
>> firing, from one thick application of the copper red glaze, so I am
>> not sure there is any point in putting an additional underlayer. I'd
>> also note that unless it was the same base glaze, it would either be
>> underfluxed or overfluxed which might cause additional problems.
>
>
> Time to re-read those Tichane books. A pure silica body is a delightfully
> elegant way to show the alumina done it.
>
> I'm mulling layer possibilities to eliminate that dark gray that soils th=
e
> rims of white stoneware. Any idea what that is?
>
>
> Jeff Lawrence
> jefflawr@gmail.com
--
----------------------------------------------------------
| |
|
