Weiland, Jeff on thu 5 may 05
Here is one for the glaze/chemistry brain trust. I have a glossy white
cone 6 glaze that has started to act up on me lately. I am firing
fairly even temp wise. The problem is that the glaze is coming out with
a crusty crystal-like surface on the outside of the pots and mostly when
the ware is at the edges of the shelves, close to the flame. It is a
Bailey 18/12 kiln. This was firing number 115, so I don't think it is a
schedule problem. I am bisque firing the work in an electric to cone 06
to burn off the garbage. What gives? I had a student pull this off the
net years ago and do not know the name or where it came from. When it is
working, it has a great marshmallow-like surface. The only material
change was that I used to use Georgia Kaolin and the last time I
ordered, Columbus Clay sent me #6 tile clay. Not sure of the
difference. Here is the recipe:
Custer Feldspar 46.86
Flint 30.09
Whiting 14.72
Georgia Kaolin 8.33
Tin Oxide 4.23
Zinc Oxide 8.23
Bentonite 3.25
Jeff Weiland
Greenfield-Central High School
810 North Broadway
Greenfield, Indiana 46140
317-462-9211
jweiland@gcsc.k12.in.us
Ron Roy on fri 6 may 05
Hi Jeff,
Two ways to melt a glaze at cone 6 - boron or zinc - if the zinc in that
glaze is getting reduced - it will evaportate - less flux - less melting.
Probably why it's happening where the flame can reduce the ZnO.
RR
>Here is one for the glaze/chemistry brain trust. I have a glossy white
>cone 6 glaze that has started to act up on me lately. I am firing
>fairly even temp wise. The problem is that the glaze is coming out with
>a crusty crystal-like surface on the outside of the pots and mostly when
>the ware is at the edges of the shelves, close to the flame. It is a
>Bailey 18/12 kiln. This was firing number 115, so I don't think it is a
>schedule problem. I am bisque firing the work in an electric to cone 06
>to burn off the garbage. What gives? I had a student pull this off the
>net years ago and do not know the name or where it came from. When it is
>working, it has a great marshmallow-like surface. The only material
>change was that I used to use Georgia Kaolin and the last time I
>ordered, Columbus Clay sent me #6 tile clay. Not sure of the
>difference. Here is the recipe:
>Custer Feldspar 46.86
>Flint 30.09
>Whiting 14.72
>Georgia Kaolin 8.33
>
>Tin Oxide 4.23
>Zinc Oxide 8.23
>Bentonite 3.25
>
>Jeff Weiland
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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