Alisa and Claus Clausen on fri 19 nov 99
------------------
Dear Clayart,
I mix up oxides with water and paint over some of my more neutral glazes for
brush work in the glaze.
I have always glazed first, and after painted the oxides on top of the =
glaze.
I am wondering if there is any fundamental difference in effect (stability =
or
bleeding, etc.) if the oxides are painted underneathe the glaze or painted =
on
top of the glaze?
In china painting I read there are both over and under glazes available, =
which
lead me think about if there is any difference in the effect.
In principle, is there a prefered method to paint with oxides, over or
underneathe the glaze?
Other than consistency of water and oxide mixture, is there a way to use =
them in
a way that they stay stable, and not bleed or run? I know that each oxide =
has
it's individual characteristics, but I am wondering if there are some rules =
of
thumb for painting with them.
Thanks and regards,
Alisa in Denmark
There are commercial underpaints and overpaints. However I have never used
them.
Cindy Strnad on sat 20 nov 99
Alisa,
If you're doing decorative ware (that is what you do, mainly, if I remember
your posts), just use the oxides/stains or whatever in any way that pleases
you. Of course you'll get a different effect from painting under versus over
the glaze. What, precisely, depends upon your glaze, your oxides, your
firing process . . . .
For food surfaces, you should take into account that painting the oxides
under the glaze is more likely to produce a safe product. (Assuming, of
course, that your glaze itself is a safe product.) Some oxides (like iron)
are less toxic than others (like manganese), and you might feel comfortable
about using them in over-glaze painting, or you may not.
If you want your over-glaze painting to stay put and not bleed, the primary
concern is in the glaze, rather than the oxide. The more matte a glaze is,
the less your painting will run.
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Rod, Marian, and Holly Morris on sat 20 nov 99
You don't mention what your firing temp and environment is. That will make a
big difference in the reply. I use all of the commercial underglaze
products, and find the Duncan Concept line (lo-fire colorantsfor oxidation)
to be very versatile both under and over glazes. I particularly like them on
top of Seattle Pottery Supply's ^05 majolica base. My experience at high
fire reduction is that under is risky. sometimes the overglaze slides off or
crawls, other times it is simply hidden. Good luck with your testing.
----- Original Message -----
From: Alisa and Claus Clausen
To:
Sent: Friday, November 19, 1999 11:54 AM
Subject: Painting with oxides under or over glazes
----------------------------Original message----------------------------
------------------
Dear Clayart,
I mix up oxides with water and paint over some of my more neutral glazes for
brush work in the glaze.
I have always glazed first, and after painted the oxides on top of the
glaze.
I am wondering if there is any fundamental difference in effect (stability
or
bleeding, etc.) if the oxides are painted underneathe the glaze or painted
on
top of the glaze?
In china painting I read there are both over and under glazes available,
which
lead me think about if there is any difference in the effect.
In principle, is there a prefered method to paint with oxides, over or
underneathe the glaze?
Other than consistency of water and oxide mixture, is there a way to use
them in
a way that they stay stable, and not bleed or run? I know that each oxide
has
it's individual characteristics, but I am wondering if there are some rules
of
thumb for painting with them.
Thanks and regards,
Alisa in Denmark
There are commercial underpaints and overpaints. However I have never used
them.
Vince Pitelka on sun 21 nov 99
Painting with oxides underglaze is fickle. Some oxides leave a powdery
surface, causing the overglaze to peel and crawl. Some oxides go through
major chemical changes in the firing, causing same. Look at the oxide, and
think about what it has to undergo during the firing. For example, cobalt
carbonate has to transform to cobalt oxide during the firing. So why not
just use cobalt oxide to begin with for you brushwork? If you use cobalt
oxide mixed with plain water underglaze, you will get no crawling. It works
great. If you use cobalt carbonate, you get crawling.
For other oxides you will have to do some experimentation. In production in
Northern California in the late 70s and early 80s, I did brush decoration
with cobalt and iron, and a very simple palette of glazes. I finally ended
up doing all my iron decoration with slip on leather hard greenware, because
I could never get away from the problem of glazes crawling over iron oxide
stains used underglaze. So why not use iron overglaze? No reason, except
that I enjoyed having the color under the glaze. Made it much easier to
handle the pots in loading the kiln. No oxides to smear. So, I applied
iron banding on the leather-hard greenware, and then applied cobalt oxide
banding and brushwork to the bisque-ware, and then the glaze. Worked great.
Good luck -
- Vince
Vince Pitelka
Home - vpitelka@DeKalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
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