Alain & Carolyn Blais on tue 30 mar 99
Help!! The following glaze is pinholing on bowls only. I have no
problems with it on plates. Any ideas about why this is happening or
suggestions for how to stop it would be greatly appreciated.
Potash Feldspar 50.4%
EPK 16.1
Whiting 19.6
Zinc Oxide 8.4
Silica 5.5
Rutile 5.0
Ilmenite- milled 1.0
Ilmenite- granular 1.0
Bentonite 1.5
I have tried reducing the rutile, as I read a high amount of this may
cause pinholing, but it didn't make any difference.
I am firing to 1195 degrees C in an electric kiln. I extended my hold
time to 35 minutes, but it doesn't seem to make a difference for those
darn bowls! Everything else with this glaze and with other glazes in my
kiln are fine.
Thanks for your help! ...Carolyn
Autumn Downey on wed 31 mar 99
Hi Carolyn,
Are the pinholes just on the outside near the base? Sometimes trimming
opens up the pores of the clay expecially if it gritty, and then if your
glaze is stiff - not sure if yours is, but the zinc might promote that, then
these pores don't heal over and there are pinholes. You could try sponging
the bowls well when they are bone dry and before bisque firing. That fills
in the pores.
Someone on clayart once suggested sponging greenware all over as a way to
prevent crawling of the glazes later. I've found that to be useful as well.
Autumn Downey
downeya@internorth.com
Yellowknife, NWT, Canada
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