Snail Scott on tue 28 feb 06
At 02:48 PM 2/28/2006 -0500, you wrote:
>...I've always used Stoneware clay
>and high-fire glazes in my classroom (9-12th grade Ceramics program). This
>year I decided to order underglazes for my upper level classes. We
>experimented with painting them on bisqueware and coating them with a cone
>6 clear glaze (I fire to cone 5 and the glaze matures fine). (And everyone
>is probably shaking their heads, knowing what I'll say next...) Most of the
>colors burned out...
Many commercial underglaze colors do well at ^6
in oxidation, but some do better than others.
Amaco's LUG line is pretty good (the 'Velvet'
line is not as refractory as the LUG's), and
the 'premium' lines that most brands offer are
also pretty good. Reds, pinks, and purples are
always the most vulnerable, though. I'd forget
them.
>...If I bisque to 04 and glaze to 06, our
>high-fire stoneware probably won't vitrify correctly, will it? Are there
>ways to correct this? And what does this mean... will the clay be fragile
>or will it just not hold water?
Both. And the glaze will tend to craze.
>...I guess I'm wondering if we can get away
>with using the 06 just for sculpture work (if it fires strong). Or... Can
>I bisque to a higher temperature and glaze fire to 06 (for functional work)?
Bisquing to vitrification makes it really tough
to apply the glaze. Not impossible, but a real
pain to get it thick enough without brushing
off the first coat as you go.
It is perfectly possible to underfire any clay,
but (as above) glazes will craze, and the result
won't be waterproof or frostproof (so, no outdoor
work, unless you're in the deep South.)
>...I'd love to
>switch to underglazes and eliminate the mixing of 25 different colors in 5
>gallon buckets - storage is a nightmare!
25 colors! Yikes! Just choose 5 or 6. These kids
will bitch, but they'll graduate, and the next crop
will be happy with what they're offered. Besides,
glazes from scratch (or even from a pre-mix) are
WAY cheaper than underglaze!
-Snail
louroess2210 on tue 28 feb 06
. This year I decided to order underglazes for my upper level
classes. We experimented with painting them on bisqueware and
coating them with a cone 6 clear glaze Most of the colors burned out.
>
> Melissa
>
Melissa, What brand of underglazes were you using.? We have used
Mayco Stroke and Coat and also
Duncan and have had very good results. Some of the colors (but not
all) would even go to cone 10.
The color charts will sometimes tell you which colors will go to the
higher temperatures.
Regards, Lou in Colorado
Melissa on tue 28 feb 06
Hi All. Please excuse this possibly "Basic" question, but I'm trying out
new products and venturing into an area that I've never explored before.
(insert theme from twilight zone here). I've always used Stoneware clay
and high-fire glazes in my classroom (9-12th grade Ceramics program). This
year I decided to order underglazes for my upper level classes. We
experimented with painting them on bisqueware and coating them with a cone
6 clear glaze (I fire to cone 5 and the glaze matures fine). (And everyone
is probably shaking their heads, knowing what I'll say next...) Most of the
colors burned out. We figured this might happen, but only had a cone 6
clear to use. I've ordered a low fire 06 clear Amaco glaze to go with the
underglazes. My real question... If I bisque to 04 and glaze to 06, our
high-fire stoneware probably won't vitrify correctly, will it? Are there
ways to correct this? And what does this mean... will the clay be fragile
or will it just not hold water? I guess I'm wondering if we can get away
with using the 06 just for sculpture work (if it fires strong). Or... Can
I bisque to a higher temperature and glaze fire to 06 (for functional work)?
My kids need the strength of the stoneware, but crave the finishes of
earthenware. Can this be accomplished with good results? I'd love to
switch to underglazes and eliminate the mixing of 25 different colors in 5
gallon buckets - storage is a nightmare! (along with keeping all those
colors properly suspended)
Help? I'd love any suggestions you have.
Melissa
Craig Clark on wed 1 mar 06
Melissa, first and formost, as you have intimated it is not a good
idea to use unvitrified clay for functional purposes. I would go a step
further and say that one should not do it. The temp at which the clay
you use vitrifies is a function of the clay body itself. I do not know
of any clay bodies that vitrify at low fire temps, at least not any
which are within the affordability range of the potting/clay artist
community.
Just keep on bisquing to 04 and use the low fired pieces for
sculptural work. I know I'm gonna get flamed for this but keeping in
mind that these are students, the long time archival quality of the work
is most probaby not as much of an issue as the activity of the making
the work itself. Also, clear and succinct explanations concerning what
vitrification of a clay body is and why we don;t want to use clay that
is not fully vitirfied for functional (as in eating from) purposes.
An under imature (not vitrified) clay body is still absorbant.
Water, food,bacteria, etc., will easily find their way into the spaces
between the clay particles. There are virtual canyons inwhich bacteria
can grow and thrive. You will have entire civilizztions growing. Not a
healthy thing. As you know the body is also not as strong, and it will
not hold water over the long haul.
One thing that you might try is to run a series of tests with your
clay body. Make several quick test pieces. Whatever you want.....little
bowls, tiles, little extrusions, whatever. Don't spend much time on
them. Fire them up in a series of bisques where you increase the temp of
the bisque with each firing. Maybe 50 degrees F or so per firing. Keep a
record of how well the clay absorbs water, or how well it takes a glaze
after each firing. YOu may find that you can substantially increase the
temp of your bisque and still be able to apply your underglazes and
glaze. Don't know if or how this little experiment will work but you
will end up with an increasing strength in the clay body. You won't have
a fully vitrified body but you will have one that is more vitrified than
the lower temp firings.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 St
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Melissa wrote:
>Hi All. Please excuse this possibly "Basic" question, but I'm trying out
>new products and venturing into an area that I've never explored before.
>(insert theme from twilight zone here). I've always used Stoneware clay
>and high-fire glazes in my classroom (9-12th grade Ceramics program). This
>year I decided to order underglazes for my upper level classes. We
>experimented with painting them on bisqueware and coating them with a cone
>6 clear glaze (I fire to cone 5 and the glaze matures fine). (And everyone
>is probably shaking their heads, knowing what I'll say next...) Most of the
>colors burned out. We figured this might happen, but only had a cone 6
>clear to use. I've ordered a low fire 06 clear Amaco glaze to go with the
>underglazes. My real question... If I bisque to 04 and glaze to 06, our
>high-fire stoneware probably won't vitrify correctly, will it? Are there
>ways to correct this? And what does this mean... will the clay be fragile
>or will it just not hold water? I guess I'm wondering if we can get away
>with using the 06 just for sculpture work (if it fires strong). Or... Can
>I bisque to a higher temperature and glaze fire to 06 (for functional work)?
>
>My kids need the strength of the stoneware, but crave the finishes of
>earthenware. Can this be accomplished with good results? I'd love to
>switch to underglazes and eliminate the mixing of 25 different colors in 5
>gallon buckets - storage is a nightmare! (along with keeping all those
>colors properly suspended)
>
>Help? I'd love any suggestions you have.
>
>Melissa
>
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>
>
>
Michael Wendt on wed 1 mar 06
Melissa,
Good news! This is the perfect class
project. Get a variety of Duncan
Concepts, Amaco Velvet underglazes
any other brands you may care to try.
Have the students prepare and label
several sets of tiles with the same sets
of colors.
Fire in the usual manner, but try some
different top coat glazes. It may well
be that one glaze will kill some of the
colors but not others so if a particular
effect is desired, using the correct
combination will solve the problem.
Educationally, this is the ideal kind of
class project because everyone can
contribute their efforts and quickly
answer your question.
Do they work? Yes. We use these
same brands at cone 10 under a clear
glaze.
Just be sure to remind them not to use
the colors on the inside of vessels for
food contact (the pigments go into
solution in glaze and may be mobile).
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Melissa wrote:
Hi All. Please excuse this possibly "Basic" question,
but I'm trying out
new products and venturing into an area that I've never
explored before.
(insert theme from twilight zone here). I've always
used Stoneware clay
and high-fire glazes in my classroom (9-12th grade
Ceramics program). This
year I decided to order underglazes for my upper level
classes. We
experimented with painting them on bisqueware and
coating them with a cone
6 clear glaze (I fire to cone 5 and the glaze matures
fine). (And everyone
is probably shaking their heads, knowing what I'll say
next...) Most of the
colors burned out. We figured this might happen, but
only had a cone 6
clear to use. I've ordered a low fire 06 clear Amaco
glaze to go with the
underglazes. My real question... If I bisque to 04
and glaze to 06, our
high-fire stoneware probably won't vitrify correctly,
will it? Are there
ways to correct this? And what does this mean... will
the clay be fragile
or will it just not hold water? I guess I'm wondering
if we can get away
with using the 06 just for sculpture work (if it fires
strong). Or... Can
I bisque to a higher temperature and glaze fire to 06
(for functional work)?
My kids need the strength of the stoneware, but crave
the finishes of
earthenware. Can this be accomplished with good
results? I'd love to
switch to underglazes and eliminate the mixing of 25
different colors in 5
gallon buckets - storage is a nightmare! (along with
keeping all those
colors properly suspended)
Help? I'd love any suggestions you have.
Melissa
brian on wed 1 mar 06
On 3/1/06, Melissa wrote:
This year I decided to order underglazes for my upper level classes. We
> experimented with painting them on bisqueware and coating them with a con=
e
> 6 clear glaze (I fire to cone 5 and the glaze matures fine). Most of the
> colors burned out.
> My kids need the strength of the stoneware, but crave the finishes of
> earthenware. Can this be accomplished with good results? >
> Help? I'd love any suggestions you have.
Melissa,
There are commercial brushable bright colours for use at higher
temperatures and I have just started experimenting with them myself.
They paint over and under a base glaze, Doesn't always mean "under"
when it says underglaze....they are stains mixed with a flux and a
medium to assist flow
It seems obvious to me to search for higher firing brushable glazes. I
cannot help with suggesting a supplier as I do not live in the USA but
I do know that you have access to heaps of ceramic suppliers there and
I hope that someone may be able to suggest one to you.
I just think it makes sense to stick with the clay and glaze that you
know and that is working for you.......just find higher firing
brushable glazes!
Brian.
--
Brian Gartside
Pukekohe, New Zealand
www.gartside.info
Alisa Liskin Clausen on wed 1 mar 06
On
> Just keep on bisquing to 04 and use the low fired pieces for
>sculptural work. I know I'm gonna get flamed for this but keeping in
>mind that these are students, the long time archival quality of the work
>is most probaby not as much of an issue as the activity of the making
>the work itself. Also, clear and succinct explanations concerning what
>vitrification of a clay body is and why we don;t want to use clay that
>is not fully vitirfied for functional (as in eating from) purposes.
>
Dear Craig,
Do as I do, not as I say. This can be pretty potent, especially with
younger people. I think it would be a good idea to make good examples to
especially students because they are just beginning to get experiences and
thus habits. The experiences they do get will weigh that much more until
they have a larger backpack. If they are allowed bad practices with
excuses for it, they may continue and say, well, even my teacher in school
did it. No flaming, but a contrary opinion.
AS for underglazes firing on stoneware, I have had these experiences.
I purchased two Amaco under glazes in the US and did not even read that
they were for cone 05. The thrill was obviously overwhelming, all those
shelves filled with all those colors. I usually mix a white underglaze
base with powdered universal colors here at home, as the pallet of
premixed under glazes is limited.
The premixed Amoco, a red and a green, cone 05 fired all right, but on the
dark side. The green was beginning to look greyish. After different
trials, I found that application was also important. As I add a higher
percent of powdered universal color to intensify the fired color, I found
that a thicker application of the premixed Amaco colors also improved the
brightness of the colors. They can go relatively thick or even dipped. I
could not, however recommend, this as a glaze alternative. It may seem
tempting because they seem reliable. Under glazes will make a dent in your
material budget as opposed to regular glazes.
A stoneware glaze on an unvitrified clay will most probably not fit. I
used to work in a free studio where the leader insisted the clay was a
white cone 04-6. It's a miracle. NOT. There were big issues with crazing.
Hope you find your solution,
Regards from Alisa in Denmark
Bonita Cohn on wed 1 mar 06
there's an article c.1995 at the ceramics web called:
TESTS OF DUNCAN UNDERGLAZES at cone 10 in Oxidation &
Reduction
http://grafik.sdsu.edu/index.html
I find it to be very useful.
Bonita in San Francisco
Bonita Cohn
http://www.bonitacohn.com
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lee love on tue 14 mar 06
--- In clayart@yahoogroups.com, Craig Clark wrote:
> I do not know
> of any clay bodies that vitrify at low fire temps, at least not any
> which are within the affordability range of the potting/clay artist
> community.
A friend of mine was working with Continental Clay's lowfire
terracotta for outdoor fountains. C.C. told her to fire to cone 1 to
vitrify the clay body for these outdoor pieces. They were not
glazed, but were decorated with oxides. It was large sculpture and
was single fired.
--
Lee In Mashiko, Japan
http://mashiko.org
http://seisokuro.blogspot.com/
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