amy parker on thu 28 oct 99
I have been reading the posts about zinc oxide really being "useless" in a
glaze, since it burns off during the firing, as I understand it from reading
the posts. I am working with a cone 6 glaze that calls for about 10% zinc
oxide, and I hate the process of having to screen it dry before adding to
the glaze mix. From what I was reading, I should be able to just leave it
out with no effects? Or did I miss something and this was maybe only for
cone 10 reduction that it burns out?
Amy, sad that the Braves were swept, but glad they made the Series again!
amy parker Lithonia, GA
amyp@sd-software.com
Wendy Hampton on fri 29 oct 99
My understanding is that zinc oxide creates crystals at cone 6 if you soak it
for an hour and the end of the firing. It works on the glazes I have tried.
Wendy
David Hendley on fri 29 oct 99
The posts about zinc oxide volatilizing apply only
to reduction firings.
Even then, I'm not convinced that zinc oxide is
'useless'. Even if it eventually goes away, it might
still be having an effect on the initial melt or the
way the glaze sinters.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----- Original Message -----
From: amy parker
To:
Sent: Thursday, October 28, 1999 12:47 PM
Subject: zinc oxide & cone 6
| ----------------------------Original message----------------------------
| I have been reading the posts about zinc oxide really being "useless" in a
| glaze, since it burns off during the firing, as I understand it from
reading
| the posts. I am working with a cone 6 glaze that calls for about 10% zinc
| oxide, and I hate the process of having to screen it dry before adding to
| the glaze mix. From what I was reading, I should be able to just leave it
| out with no effects? Or did I miss something and this was maybe only for
| cone 10 reduction that it burns out?
|
| Amy, sad that the Braves were swept, but glad they made the Series again!
| amy parker Lithonia, GA
| amyp@sd-software.com
|
Ron Roy on fri 29 oct 99
Hi Amy,
It's when zinc oxide is reduced that the problem arises. This is not to say
it can't happen to some degree in oxidation firings - this is probably the
reason pinholing is blamed on zinc - and why it is recommeded to keep the
amount no more that 2%.
There is no reason you cannot have clean firings - I would think using a
vent would do a lot to prevent zinc reduction.
No reason you have to screen dry - mix it in with the water and use a paint
mixer in a drill before you screen.
RR
>----------------------------Original message----------------------------
>I have been reading the posts about zinc oxide really being "useless" in a
>glaze, since it burns off during the firing, as I understand it from reading
>the posts. I am working with a cone 6 glaze that calls for about 10% zinc
>oxide, and I hate the process of having to screen it dry before adding to
>the glaze mix. From what I was reading, I should be able to just leave it
>out with no effects? Or did I miss something and this was maybe only for
>cone 10 reduction that it burns out?
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Jeff Lawrence on fri 29 oct 99
Amy Parker was wondering about zinc oxide at lower temps than cone 10
Hi Amy,
I have some ^04 glazes that look good in electric oxidation, wretched in
gas oxidation. I attribute the difference to the zinc oxide.
Best
Jeff
Jeff Lawrence Sun Dagger Design
jml@sundagger.com Rt. 3 Box 220
www.sundagger.com Espanola, NM 87532
vox 505-753-5913 fax 505-753-8074
John Rodgers on sat 30 oct 99
Amy, the zinc oxide acts as a flux in electric oxidation. It works well with
many glazes in electric firings, but you are right, in a gas firing it burns
right out and goes up the chimney. If you are going to use gas...get rid of the
zinc oxide
John Rodgers
amy parker wrote:
> ----------------------------Original message----------------------------
> I have been reading the posts about zinc oxide really being "useless" in a
> glaze, since it burns off during the firing, as I understand it from reading
> the posts. I am working with a cone 6 glaze that calls for about 10% zinc
> oxide, and I hate the process of having to screen it dry before adding to
> the glaze mix. From what I was reading, I should be able to just leave it
> out with no effects? Or did I miss something and this was maybe only for
> cone 10 reduction that it burns out?
>
> Amy, sad that the Braves were swept, but glad they made the Series again!
> amy parker Lithonia, GA
> amyp@sd-software.com
Cerere@aol.com on sat 30 oct 99
FROM THE CERAMIC SPECTRUM by ROBIN HOPPER, p.146:
"Zinc Oxide. Zinc is primarily used as a fluxing agent for mid to high
temperature glazes. It can, however, perform a dual function in the
production of opaque glazes. It has a strong effect on many colorants,
turning iron anywhere from pale yellow to mustard brown, chromium to brown,
cobalt to grey blue, and nickel to blue, green or brown."
Paul Lewing on sat 30 oct 99
Wendy Hampton wrote:
>
> ----------------------------Original message----------------------------
> My understanding is that zinc oxide creates crystals at cone 6 if you soak it
> for an hour and the end of the firing. It works on the glazes I have tried.
> Wendy
Hi, Wendy.
This isn't quite exact, but you're on the right track. What most people
think of as crystal glazes, those ones with the big spider-web crystals,
are indeed zinc glazes, sometimes at cone 6, sometimes higher. But
that's not all there is to it. In order to really get those crystals,
your zinc glaze must also have virtually no alumina, and the temperature
must be dropped 100 degrees or so and held there for a while. Crystal
glazes typically have a Si:Al ratio of 70 or so, sometimes even 100 or
more, in contrast to most normal glazes' 5 to 15. By the way, the
opposite end of this ratio spectrum is the so-called "lichen glazes",
with ratios around 2.
But firing any zinc glaze and soaking it would probably produce some
crystals, probably more so than most other kinds of glazes. I have
fired real crystal glaze recipes on my normal schedule and gotten, not
the big webby crystals, but lots of smaller crystals that looked like
snowflakes.
And for the information of the person who originally posted this thread,
it's not that the zinc disappears at high temperature, it's that the
least bit of reduction appears to convert the zinc oxide to the metal
zinc, which boils off at a very low temperature. So zinc oxide could
still be a useful flux even at cone 10, but only in oxidation.
Paul Lewing, Seattle
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