Jeff Lawrence on fri 15 mar 02
Snail was recommending CMC to de-dusticate your oxide...
Another good additive is glycerin if you're brushing on bisque
ware because the stuff doesn't get sucked out of the
brush so quickly. I found I preferred brushing onto greenware.
A lot of times the bisque fire will "set" the naked oxide
but it works better if you mix it in with a little frit as
Snail suggests or a little bit of some neutral glaze. Also,
Jeff Lawrence
jml@cybermesa.com
Snail Scott on fri 15 mar 02
At 12:36 PM 3/14/02 -0500, Rose wrote:
> I tried using a blue oxide on the porcelain then a white glaze over
that and
>it curdled and crawled and generally looked like it had some kind of
disease...
There's probably nothing wrong with your glaze.
The trouble with oxide washes is that oxides are dusty.
It's like adding dust to your bisque right after you went
through all that trouble to clean it! When you glaze over
the oxide, it's like glazing dusty bisque, and it can
crawl off as soon as the glaze starts to melt, since it's
not really stuck to anything underneath except that dusty
oxide layer.
Try mixing your oxide with a little CMC to help glue it
together while glazing, a little white clay to make it
easier to handle, and a little frit to help it fuse in
firing. Or, use underglazes instead of pure oxide. This
is the sort of thing they're designed for, after all.
They already have the CMC and clay and frit in them, and
it's easier to control the final color, since they're not
as concentrated as a pure oxide. (A little cobalt goes a
long way, as you've probably noticed!) You can buy the
commerical brands (most work OK at ^6, and some will even
do ^10), or you can mix your own from simple recipes.
-Snail
vince pitelka on sat 16 mar 02
> Is this true for cobolt carbonate that was mixed into a porcelain body as
> well. I have only bisqued the pieces and have not fired them yet. I was
> just going to try using a clear glaze.
Judy -
This will not be a problem. Adding cobalt carb to a clay is just like
adding it to a slip. The problem arises when pure cobalt carbonate mixed
with water is brushed on over bisque ware, which is then glazed. The glaze
does not attach properly to the powdery cobalt carb, and in melting crawls
away from that area. It is an ugly defect with little possibility of
repair. As I mentioned, cobalt oxide generally works fine under a glaze.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Craig Martell on sat 16 mar 02
Hi:
Another quick post before the gooroos return.
Snail and Jeff have already forked over some good info but I'll venture my
opinion too. They've both said that the problem is from dusty oxides under
the glaze and that's the truth. I've used straight watered oxides on
bisque and green pots and I've found the same problem so I always put the
colorant in some sort of "media" to arrest the crawling problem. I use
slips made from my porcelain body and add colorant. No crawling. You can
use a good fusible glaze too and add up to 50% colorant and this will
virtually eliminate crawling.
later, Craig Martell in Oregon..........it just stopped snowing a minute ago.
vince pitelka on sat 16 mar 02
> I tried using a blue oxide on the porcelain then a white glaze over
> that and it curdled and crawled and generally looked like it had some kind
of
> disease...
Rose -
Cobalt carbonate is especially powdery and refractory, and glazes will
almost always crawl when it is used underglaze. I do not recommend trying
to add anything to the carbonate to make it work underglaze unless you
decide to use a true engobe formulated for application to bisqueware.
Otherwise, use cobalt oxide. It generally works fine underglaze with little
or no problems.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Judith Frederick on sun 17 mar 02
Vince,
Is this true for cobolt carbonate that was mixed into a porcelain body as
well. I have only bisqued the pieces and have not fired them yet. I was
just going to try using a clear glaze.
Judy
>From: vince pitelka
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: crawling over oxide
>Date: Sat, 16 Mar 2002 17:02:36 -0600
>
> > I tried using a blue oxide on the porcelain then a white glaze over
> > that and it curdled and crawled and generally looked like it had some
>kind
>of
> > disease...
>
>Rose -
>Cobalt carbonate is especially powdery and refractory, and glazes will
>almost always crawl when it is used underglaze. I do not recommend trying
>to add anything to the carbonate to make it work underglaze unless you
>decide to use a true engobe formulated for application to bisqueware.
>Otherwise, use cobalt oxide. It generally works fine underglaze with
>little
>or no problems.
>Best wishes -
>- Vince
>
>Vince Pitelka
>Appalachian Center for Crafts
>Tennessee Technological University
>1560 Craft Center Drive, Smithville TN 37166
>Home - vpitelka@dtccom.net
>615/597-5376
>Work - wpitelka@tntech.edu
>615/597-6801 ext. 111, fax 615/597-6803
>http://www.craftcenter.tntech.edu/
>
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John Baymore on mon 18 mar 02
Another quick post before the gooroos return.
Ppppssssssttttttt ..... hey Craig.................... you ARE one .
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
"DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop =
August 16-25, 2002"
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