Daniel Shevitz on mon 15 apr 96
Hi All,
I have a problem with a cone 5 glaze cracking when still green. If I double dip
this glaze on top of another (it's a rutile glaze by the way), it peels off in
sheets. It doesn't really seem to matter too much what the bottom glaze is. It
also has a tendency to crack even when used alone. The glaze has 5% EPK by
weight. Can anyone give any ideas to correct the problem? Should I switch to
Ball clay? calcined EPK? etc...
thanks,
Danny
Gail Nichols on tue 16 apr 96
>----------------------------Original message----------------------------
>Hi All,
>
>I have a problem with a cone 5 glaze cracking when still green. If I double dip
>this glaze on top of another (it's a rutile glaze by the way), it peels off in
>sheets. It doesn't really seem to matter too much what the bottom glaze is. It
>also has a tendency to crack even when used alone. The glaze has 5% EPK by
>weight. Can anyone give any ideas to correct the problem? Should I switch to
>Ball clay? calcined EPK? etc...
>
>thanks,
>Danny
>
>
By"green", do you mean you're applying the glaze when the clay is leather
hard, or bone dry?
Is EPK a form of kaolin (I'm unfamiliar with the term here in Australia).
Anyway, it sounds as if your glaze recipe is probably low in clay content,
and particularly low in the sort of clay content that will give a good
shrinkage rate. If this is so, then using ball clay should help, by
increasing the shrinkage of the glaze. Adding bentonite will also help.
Calcining the EPK would have the opposite effect....it would decrease the
shrinkage rate of the glaze. If your problem were due to a high clay
content of the glaze, this might help, especially if you were applying the
glaze to bisque ware. But from the wording of your question, it's not likely.
Gail
_______________________________
Gail Nichols
Sydney, Australia
gail@matra.com.au
http://www.matra.com.au/~gail/
Ron Roy on tue 16 apr 96
Hey Danny,
I don't know what else you have in that glaze but, to get the same amount
of Al2O3 and SiO2 sub 6 ball for 5 EPK amd lower silica by 1.5. I would
advise adding 1% bentonite as well.
Let us know if this works - if not, send me the recipe and I will make
other suggestions.
Ron Roy, Toronto, Canada
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