William Lucius on sat 18 aug 12
I recently began experimenting with Black Iron Oxide painted designs under =
=3D
my cone 5 white carbon trap glaze in the hopes of obtaining a reasonable fa=
=3D
csimile of Prehistoric Pueblo black-on-white pottery. Manganese Dioxide co=
=3D
nsistently comes out brown under the glaze as does Red Iron Oxide. To my s=
=3D
urprise the BIO came out blue instead of the expected black! I consistentl=
=3D
y fire the glaze in light reduction. The glaze recipe is as follows:Ball Cl=
=3D
ay 21.3Gerstly Borate 14.9Lithium Carbonate 4.3 =
=3D
=3D20
Nepheline Syenite 37.2Silica 22.3Zirocopax =
=3D
7.0 + Bentonite 2.0 My knowledge of chemistry is insufficien=
=3D
t to inform me as to what in the glaze interacts with the BIO to throw it b=
=3D
lue. Does anyone out there have any ideas? =3D20
William A. Lucius=3D2C Ph.D.
Board President and Director
Institute for Archaeological Ceramic Research (IACR)
iacr@msn.com
http://leuppkilnconferenceorg.admin.melbourneitwebsites.com/
=3D20
=3D
Robert Harris on sun 19 aug 12
A total guess, but at Cone 10 I get a blue/green (blue on brown/amber)
boron phase separation with both Red and Black IO.
Since at Cone 10 both BIO and RIO convert to FeO I suspect that something
similar is happening with BIO (FeO.Fe2O3? aka Fe3O4) at Cone 5.
My guess is that somehow the FeO moiety in BIO is inducing a 0.45-0.5
micron boron glass phase separation in your glaze, which reflects blue
wavelengths.
I think (I am currently doing experiments to prove this), that this
requires high alkali (vs Calcium) levels - which your glaze, at first
glance, seems to have.
Alternatively I have also seen strong blue when a highly alkaline, fluid
glaze is used over a high iron tenmoku (also at Cone 10). This happens in
the absence of boron, and I am less certain of the mechanism, however I
have never seen it with a single glaze (although since you are
underpainting BIO I don't know that this latter fact means anything.)
Hope that sheds a little light, rather than increase the confusion!
Robert
On Sat, Aug 18, 2012 at 10:47 PM, William Lucius wrote:
> I recently began experimenting with Black Iron Oxide painted designs unde=
r
> my cone 5 white carbon trap glaze in the hopes of obtaining a reasonable
> facsimile of Prehistoric Pueblo black-on-white pottery. Manganese Dioxid=
e
> consistently comes out brown under the glaze as does Red Iron Oxide. To =
my
> surprise the BIO came out blue instead of the expected black! I
> consistently fire the glaze in light reduction. The glaze recipe is as
> follows:Ball Clay 21.3Gerstly Borate 14.9Lithium
> Carbonate 4.3
> Nepheline Syenite 37.2Silica 22.3Zirocopax
> 7.0 + Bentonite 2.0 My knowledge of chemistry is
> insufficient to inform me as to what in the glaze interacts with the BIO =
to
> throw it blue. Does anyone out there have any ideas?
> William A. Lucius, Ph.D.
>
> Board President and Director
>
> Institute for Archaeological Ceramic Research (IACR)
> iacr@msn.com
> http://leuppkilnconferenceorg.admin.melbourneitwebsites.com/
>
>
>
>
--
----------------------------------------------------------
William & Susan Schran User on sun 19 aug 12
On 8/18/12 10:47 PM, "William Lucius" wrote:
>I recently began experimenting with Black Iron Oxide painted designs
>under my cone 5 white carbon trap glaze in the hopes of obtaining a
>reasonable facsimile of Prehistoric Pueblo black-on-white pottery.
>Manganese Dioxide consistently comes out brown under the glaze as does
>Red Iron Oxide. To my surprise the BIO came out blue instead of the
>expected black! I consistently fire the glaze in light reduction. The
>glaze recipe is as follows:Ball Clay 21.3Gerstly Borate
> 14.9Lithium Carbonate 4.3
>Nepheline Syenite 37.2Silica 22.3Zirocopax
> 7.0 + Bentonite 2.0 My knowledge of chemistry is
>insufficient to inform me as to what in the glaze interacts with the BIO
>to throw it blue. Does anyone out there have any ideas?
This from the Digital Fire web site:
* In reduction glazes Fe2O3 tends to fire bluish or turquoise to apple
green with high soda (boric oxide may enhance). 0.5% iron with K2O may
give delicate blue to blue green.
* Oxides - FeO The presence
of phosphorous pentoxide, lithia and soda also encourage blue in both
normal and saturation conditions in reduction firing. Iron glazes will
move toward blue if alumina is low.
I would have expected a brown color from the iron instead of the blue.
As you can read what I have copied, it would seem the lithium may be the
material pushing the iron towards blue.
You may need to try a black stain to obtain a black color.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Des & Jan Howard on sun 19 aug 12
Robert
Try small amounts of barium instead of calcium, say 2%
barium carbonate. This appears to promote blue celadon.
Though the colour of celadons are solution based not
colloid based as in your phase separation test it may
be worth a whirl.
Des
On 19/08/2012 3:56 PM, Robert Harris wrote:
> My guess is that somehow the FeO moiety in BIO is inducing a 0.45-0.5
> micron boron glass phase separation in your glaze, which reflects blue
> wavelengths.
>
> I think (I am currently doing experiments to prove this), that this
> requires high alkali (vs Calcium) levels - which your glaze, at first
> glance, seems to have.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
-32.656072 149.840624
James Freeman on sun 19 aug 12
On Sat, Aug 18, 2012 at 10:47 PM, William Lucius wrote:
I recently began experimenting with Black Iron Oxide painted designs under
my cone 5 white carbon trap glaze in the hopes of obtaining a reasonable
facsimile of Prehistoric Pueblo black-on-white pottery. Manganese Dioxide
consistently comes out brown under the glaze as does Red Iron Oxide. To my
surprise the BIO came out blue instead of the expected black!
William...
The iron is likely turning blue for the same reason it does in blue or
green celadon. You can reduce less, but then it will probably be brown.
It may also be turning blue due to some sort of phase separation or
diffraction issues, as Robert suggests.
Whatever the underlying reason, instead of a single oxide try using a mix
of iron, copper, and cobalt, and if you are not afraid of them, a bit of
manganese and a soup=3DE7on of chrome. The proportions are not terribly
important.
Glaze colorants (or stain) work by absorbing most wavelengths of light
(colors), and reflecting only those in a narrow band. Iron, for example,
absorbs everything except those in the reddish band (or blue or green, if
in very small proportions and fired in reduction). Add some cobalt, and it
will absorb a lot of that reddish-brown light. It will want to reflect the
blue wavelengths, but those are partially absorbed by the iron that is also
in there. Likewise, an added bit of copper will want to absorb anything
but green, but the green light it is trying to reflect is already absorbed
by the iron and cobalt. This is a simplification, but it demonstrates that
the more colorants you toss into the mix, the fewer wavelengths of light
will be reflected, and thus the "blacker" the glaze or oxide wash will be.
Look at the formula for Mason 6600 or any other black stain, and you will
see all of the usual colorants in the batch.
Another idea might be to mix your black colorants into a slip rather than
using them as an oxide wash. The slip will tend to bind the colors a bit,
thus decreasing their availability to be absorbed into your glaze melt.
Good luck with your project.
...James
James Freeman
"Talk sense to a fool, and he calls you foolish."
-Euripides
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
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