Cbaker on mon 20 mar 06
I'm off on a new path again and struggling with the learning curve. =
I'm drawing with inks on bisque...Bmix and porcelain. The community =
studio clear glaze burns out one of my inks. The ink is a mix of =
Redart, RIO, and EPK. This is a beautiful coppery tan on bare clay. =
When I cover it with the clear on the inside of a bowl the ink =
disappears. My chrome and cobalt based inks are ok under the clear. I =
don't know what is in the clear, but will find out next week in class.
Could anyone suggest some clear glazes that I could test over the Redart =
ink that wouldn't burn out the color? This ink looks beautiful on bare =
clay with a shino or O'Hara khaki around it. I like drawing on the bare =
clay rather than on top of the glaze, so I would like to cover the ink =
with a clear.
Any suggestions would be appreciated.
Carol Baker
Scottsdale, Arizona
Vince Pitelka on mon 20 mar 06
Carol Baker wrote:
"I'm off on a new path again and struggling with the learning curve. I'm
drawing with inks on bisque...Bmix and porcelain. The community studio
clear glaze burns out one of my inks. The ink is a mix of Redart, RIO, and
EPK. This is a beautiful coppery tan on bare clay. When I cover it with
the clear on the inside of a bowl the ink disappears. My chrome and cobalt
based inks are ok under the clear. I don't know what is in the clear, but
will find out next week in class.
Carol -
A handy aphorism in ceramics is "The glaze feeds off the body." That means
that the glaze always has some solvent effect upon the body at the
clay-glaze interface. It is more true with high-fire wares, where there is
much more thermochemical activity, but at any temperature the glaze will
dissolve a little bit of whatever is on the surface of the body. The cobalt
and chrome are such powerful colorants that they endure that little bit of
solvent action, whereas the iron and especially the redart are far weaker,
and are simply absorbed. You could try doing your drawing with a commercial
brown underglaze? Even then you may have to go over your lines several
times, and that might remove some of the spontaneity. I don't know what
kind of drawing you are doing, but you will have to do some experimenting.
If you want to experiment with other "inks," first, eliminate the redart and
the EPK - they are both just diluting your colorant. You may need to use
some gum medium (CMC gum) and a little non-toxic antifreeze (propylene
glycol - nice brushing-flowing medium) with the colorant. If you can draw
with just iron with a minimal addition of these ingredients, you might get
enough concentration to show under the glaze. Also, the amount of glaze is
going to make a big difference. You might want to water down the glaze a
bit and just use a thin coat and see what that does.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Charles Manuel on tue 21 mar 06
Carol,
Calcium bleaches iron. There must be a lot of calcium in your glaze to =
bleach a concentrated amount of iron as you describe.
Chuck Manuel
________________________________
From: Clayart on behalf of Vince Pitelka
Sent: Mon 3/20/2006 9:39 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Help? Clear glaze ^10 reduction, ink burning out
Carol Baker wrote:
"I'm off on a new path again and struggling with the learning curve. =
I'm
drawing with inks on bisque...Bmix and porcelain. The community studio
clear glaze burns out one of my inks. The ink is a mix of Redart, RIO, =
and
EPK. This is a beautiful coppery tan on bare clay. When I cover it =
with
the clear on the inside of a bowl the ink disappears. My chrome and =
cobalt
based inks are ok under the clear. I don't know what is in the clear, =
but
will find out next week in class.
Carol -
A handy aphorism in ceramics is "The glaze feeds off the body." That =
means
that the glaze always has some solvent effect upon the body at the
clay-glaze interface. It is more true with high-fire wares, where there =
is
much more thermochemical activity, but at any temperature the glaze will
dissolve a little bit of whatever is on the surface of the body. The =
cobalt
and chrome are such powerful colorants that they endure that little bit =
of
solvent action, whereas the iron and especially the redart are far =
weaker,
and are simply absorbed. You could try doing your drawing with a =
commercial
brown underglaze? Even then you may have to go over your lines several
times, and that might remove some of the spontaneity. I don't know what
kind of drawing you are doing, but you will have to do some =
experimenting.
If you want to experiment with other "inks," first, eliminate the redart =
and
the EPK - they are both just diluting your colorant. You may need to =
use
some gum medium (CMC gum) and a little non-toxic antifreeze (propylene
glycol - nice brushing-flowing medium) with the colorant. If you can =
draw
with just iron with a minimal addition of these ingredients, you might =
get
enough concentration to show under the glaze. Also, the amount of glaze =
is
going to make a big difference. You might want to water down the glaze =
a
bit and just use a thin coat and see what that does.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
_________________________________________________________________________=
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Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at =
melpots@pclink.com.
Ruth Ballou on tue 21 mar 06
Hi Carol,
Without seeing the recipe for the glaze or the slip/underglaze (ink),
I'm going to venture that the iron is not burning out. Rather, what's
happening is related to the solubility of the RIO in the glaze. Iron
bearing glazes, which essentially you've created by using RIO under a
clear glaze, can give a tremendous range of colors and effects,
starting with pale blue/green celadons, to honey, tenmoku, kaki,
tessha, teadust or oilspot. Each color will depend on a variety of
factors: the percentage of iron, the percentage of calcium in the
glaze, the alumina/silica ratio of the glaze, the presence of
magnesium, as well as the firing and cooling. Small amounts of iron
in a clear glaze may dissolve completely or produce a pale celadon or
honey colored glaze. The higher the calcium content of the glaze, the
more easily this will happen. As the iron is increased in the base
glaze and the alumina/silica ratio is varied, the iron will dissolve
during the firing and crystallize out during the cooling to produce
kaki, tessha or tea dust. If the glaze is cooled quickly so that the
iron does not have time to crystallize, shiny black tenmoku will
result. Iron content of these glazes ranges from 8 - 20%. By
contrast, shino glazes contain very little calcium, so a very small
amount of iron will give color. For a more complete discussion of
both high and low iron glazes, find a copy of Ian Currie's Stoneware
Glazes: A Systematic Approach and see chapters 20 and 21. For the
short term, I'd suggest looking for a glaze that is high in feldspar
and uses fluxes other than whiting or wollastonite, or at least keeps
these two very low. Also try increasing the intensity of the
underglaze, either by increasing the iron content in a line blend, or
simply by applying it more heavily.
Ruth Ballou
Belgium
On Mar 20, 2006, at 7:21 PM, Cbaker wrote:
> I'm off on a new path again and struggling with the learning
> curve. I'm drawing with inks on bisque...Bmix and porcelain. The
> community studio clear glaze burns out one of my inks. The ink is
> a mix of Redart, RIO, and EPK. This is a beautiful coppery tan on
> bare clay. When I cover it with the clear on the inside of a bowl
> the ink disappears. My chrome and cobalt based inks are ok under
> the clear. I don't know what is in the clear, but will find out
> next week in class.
>
> Could anyone suggest some clear glazes that I could test over the
> Redart ink that wouldn't burn out the color? This ink looks
> beautiful on bare clay with a shino or O'Hara khaki around it. I
> like drawing on the bare clay rather than on top of the glaze, so I
> would like to cover the ink with a clear.
>
> Any suggestions would be appreciated.
>
> Carol Baker
> Scottsdale, Arizona
>
> ______________________________________________________________________
> ________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
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