Barbrox@aol.com on wed 29 jan 97
Dear Ron
I appreciate your taking the time to respond to my problem. I believe that
you are correct regarding what will happen to my re-fires as I have indeed
tried this and the results have truly been worse. What I am still having some
problems understanding is why previous use of the same clay and the same
glaze worked just fine. (I did just buy a new batch of the glaze.) As I await
the arrival of my new Skutt 1027 complete with Envirovent and automatic
controls, can I assume that this system will control the fire as you
described? Well, I suppose that I will try firing a bisque load again. P.S. I
do not have an element out.Thanks again- Barbara
Gordana Ricijas on thu 7 feb 02
We have problem with blisters after inglaze decor
firing at 1260-1300°C (cone 8/10). The atmosphere in
the kiln is oxidation.
We produce high-fired hotel porcelain. Temperature of
our glaze kiln is 1360°C (cone 12/13), oxidation and
reduction atmosphere.
Characteristic of glaze:
- sintering 1170°C
- softening 1180°C
- 1/2 sphere 1290°C
- fusion 1310°C
What do you sugest us to solve this problem?
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Gordana Ricijas on mon 4 mar 02
Hi!
I found a glaze recipe on internet with wollastonite:
Recipe:
20,5 Kaolin
26,5 Silica
27,0 Custer feldspar
23,5 Wollastonite
2,5 Zinc Oxide
Add:
0,5 Soda
I didn't use ZnO, I use higher silica. Kiln: gass kiln ox. and reduction, 1360°C.
I have a big problem with wollastonite. It settled down so I have to mix the slurry strong.
Do any of you have similar experience? What do you sugest to do?
It is interesting that blisters after inglaze decor firing at 1270°C appear only on plates, on the bottom of plates (not on cups and bowls), so we have to fire most of decors at 1300°C instead at lower temperature. This blisters look like a craters. When we refired plate with blisters in decor kiln, some blisters disepear.
If it is problem in glaze recipe, why blisters don't appear on cups and bowls? What do you think?
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Cindy Strnad on mon 4 mar 02
Dear Gordana,
Blisters can be caused when gasses and trapped air move upward from the body,
and then through the glaze. If the glaze is thick, the blisters will be worse.
Make sure you do not apply the glaze more thickly on the plates than on the
bowls and cups. If a pottery piece has thicker walls, the glaze will go on more
thickly when you apply it to the pot. This may be the problem with your plates.
Are they thicker than your cups and bowls?
To get rid of blisters: Soak the kiln at top temperature and cool very slowly--
OR: Fire and cool quickly so that the air and gasses do not have time to collect
and rise through the glaze.
Apply glazes more thinly
Fire to a higher bisque temperature. This may help to burn off gasses in the
clay. You could also soak the bisque load at top temperature to give gasses more
time to escape.
Wollastonite is a good and reliable material, but it is inconvenient to use. If
you are using wollastonite, you must sieve or strain your glazes. Once you have
done this, the wollastonite (by itself) will give you no more problems.
Sometimes other chemical reactions may cause crystals to grow in your glaze. If
this happens, you will need to sieve the glaze again. I use an 80 mesh sieve.
You will need a fine sieve, but I do not think you will need one as fine as 80
mesh.
Best wishes,
=====================================
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
CM Critique discussion forum
http://www.earthen-vessels-pottery.com/toforum.html
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