Marni Turkel on fri 20 jun 97
Three years ago I was working on a brown glaze for cone 5 oxidation. I
started with a glaze formula from Zakin's Electric Kiln Ceramics and came
up with a color and surface I liked, but when I put water in a vase glazed
inside and out with it, it didn't just sweat, it literally oozed out of the
vase. I had never seen anything like it before. Within an hour, beads of
water formed on the sides of the vase in a wide (1" square) crazing
pattern. I stopped working on that glaze.
I have since changed clay bodies, and thought I would revisit the glaze.
The original formula calls for barium carbonate. I had subsituted strontium
for it 1 to 1 when I tried it before, also I had substituted petalite for
spodumene. I just fired up two tests of the base glaze (no colorants): one
with barium and the other with 75% substitution of strontium. To test for
sweating I put water in the pieces and set them on a clean sheet of yellow
legal pad paper. It is low tech, but it works for me, if I can see any
rippling of the paper where the piece sat, it isn't ok. The piece glazed
with the barium version showed no trace of water on the paper, the
strontium version left the paper krinkled and soggy.
Barium Formula
Frit 3124: 18.
Magnesium carbonate: 7.
Neph syenite: 10.
Baruim carbonate: 15
Petalite: 15.
EPK: 10.
Whiting: 13
Strontium Formula
Frit 3124: 18.
Magnesium carbonate: 7.
Neph syenite: 10.
Strontium carbonate: 11.25
Petalite: 15.
EPK: 10.
Whiting: 13
I would prefer not to use barium if possible. Any help understanding this
problem would be a great help. A solution would be even better.
Thank you
Marni Turkel
Stony Point Ceramic Design
Santa Rosa, California
Karl P. Platt on sat 21 jun 97
The problem has less to do with the presence of any particular material
than the entire composition. The "glaze", both inside and outside the
vase was cracked and/or porous and the body is/was highly porous.
The glaze actually figures to something that looks more like an engobe
-- one assumes this material is quite dry looking after a cone 5 firing.
Ditch the glaze and try something else
KPP
Ron Roy on mon 23 jun 97
>I have since changed clay bodies, and thought I would revisit the glaze.
>The original formula calls for barium carbonate. I had subsituted strontium
>for it 1 to 1 when I tried it before, also I had substituted petalite for
>spodumene. I just fired up two tests of the base glaze (no colorants): one
>with barium and the other with 75% substitution of strontium. To test for
>sweating I put water in the pieces and set them on a clean sheet of yellow
>legal pad paper. It is low tech, but it works for me, if I can see any
>rippling of the paper where the piece sat, it isn't ok. The piece glazed
>with the barium version showed no trace of water on the paper, the
>strontium version left the paper krinkled and soggy.
Hi Marni,
The calculations for both those glazes indicate they will craze. The barium
one will probably craze eventually. The real problem is the body. It it
were vitrified enough it would not let the water through. Get a different
body or fire the one you have up farther to make it water proof.
Both those matt glazes are short of silica and will not be durable in
anyway by the way.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/ronroy.htm
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