Jay Gertz on fri 2 oct 98
Hi clay folk!
I have made a tile mural for outdoor installation. I applied
underglazes before bisque firing, and then again after. I have not glaze
fired this work yet. I have since noticed that these Amaco underglazes
tend to burn off or change color after glaze firing to cone 5. (It
seems to depend on their color, reds and pinks changing more than the
browns, yellows, etc.) Okay, I put a lot of work into painting this
mural and hate to ruin it by going ahead and firing it to cone 5. It
was my first time at any sort of tile work and kinda went overboard on
my initial project with this mural. It's about 2 x 4 ft. I plan on
applying a clear glaze over the underglazes.
The clay body matures at 4-6, if I'm not mistaken. Is it possible to
fire it lower than that and hope it will stay sound outdoors? Or
should I fire it a couple of times, once at say 02 and see how it looks
then again higher? It will not be directly in the elements, but mounted
on a wall under an overhang, in a garden setting.
Thanks, Jay Gertz (jgertz@bulldog.unca.edu)
Cindy on sat 3 oct 98
Jay,
Your ceramics supply house should have a chart detailing how the various
underglazes will look after firing to within varying ranges. In addition to
using that information, I recommend you test to see how high you can go
without burning out your reds, etc. I suspect the maximum they're likely to
tolerate will be less than ^2.
Since your mural will be out of the elements, it will likely do all right
even when fired to a lower temp than the clay's maturation point. Whether
or not the glazes will fit is another matter. But then, that may not be
terribly vital on a mural. Hope it works out well for you.
Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm
----------
> From: Jay Gertz
> To: CLAYART@LSV.UKY.EDU
> Subject: Clay maturation/underglazes
> Date: Friday, October 02, 1998 11:28 AM
>
> ----------------------------Original message----------------------------
> Hi clay folk!
> I have made a tile mural for outdoor installation. I applied
> underglazes before bisque firing, and then again after. I have not glaze
> fired this work yet. I have since noticed that these Amaco underglazes
> tend to burn off or change color after glaze firing to cone 5. (It
> seems to depend on their color, reds and pinks changing more than the
> browns, yellows, etc.) Okay, I put a lot of work into painting this
> mural and hate to ruin it by going ahead and firing it to cone 5. It
> was my first time at any sort of tile work and kinda went overboard on
> my initial project with this mural. It's about 2 x 4 ft. I plan on
> applying a clear glaze over the underglazes.
> The clay body matures at 4-6, if I'm not mistaken. Is it possible to
> fire it lower than that and hope it will stay sound outdoors? Or
> should I fire it a couple of times, once at say 02 and see how it looks
> then again higher? It will not be directly in the elements, but mounted
> on a wall under an overhang, in a garden setting.
> Thanks, Jay Gertz (jgertz@bulldog.unca.edu)
>
"Terry Sullivan/Nottingham Center for the Arts. San Marcos," on sat 3 oct 98
Jay,
I'm no expert on low/medium fire underglazes but have picked up a few
excellent tips along the way.
Did an excellent workshop with Orton tech. personel on underglaze firing.
Learned: red/yellows are especially sensitive to overfiring, any reduction and
many of the clay burnoff products. This means gas firing will be particularly
difficult and even electric is not truely pure oxidation.
There's lots of stuff comming out of clay and glazes during a firing,
espescially between 400-1000 degrees F. Chemicaly combined water, Carbonates
(can be lots of toxic carbon monoxide from a bisque fire), Sulfates etc . The
Tech showed us very dramatic examples of test tiles fired in the same
electric kiln. One firing normal and the other using the Orton bottom draw
kiln vent. The reds were incredibly bright and overall consistantly saturated
on tiles fired in a vented electric kiln.
Orton is a non-profit foundation and this persons whole job was to reasearch ,
test and diseminate technical clay information. He was not selling Orton Kiln
Vents.
He was such a fountain ofusefull information that the presenter, Laguna Clay
Co., practicaly had to throw us participants out at the end of the day.
I'm fairly sure that much of this information is available from Orton.
Don't have address handy but any ceramic supplier and most issues of Ceramic
Monthly will.
Hope this helps,
Terry Sullivan
Nottingham Center for the Arts
PS- The above explains why it is dangerous to be in a poorly vented room
during a large bisque firing. Any body else got a headache under those
circumstances ?
Orton has qualitativly measured the NO and NO2 ( along with all the other
stuff) that comes off raw clay during bisque in an electric kiln.
Gayle Pritchard on sun 4 oct 98
Jay,
Since you re-applied your underglazes after the bisque, you should run your
tiles through a bisque again to prevent them from smearing, or bleeding, when
you apply the clear glaze. Amaco HF-9 Zinc-Free Clear will give the best
results over underglazes at cone 5-6. You should get minimal fading, but, do
a test tile first.
Good luck!
Gayle
GPritch101@aol.com
Clearwater, FL
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