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funnel cracks

updated wed 2 sep 98

 

Sandra Gekosky on tue 1 sep 98

To all you experts who throw funnel shapes on the wheel:

This is a new form for me......the funnel.
To practice, I threw six 2.5 # balls into funnels.
Everyone survived.

My goal was to make bird house lids.
I threw the same funnel shape using 3.5 # balls of clay.
50 % have cracks leading from the small opening down.
(of course, these do not have the long, skinny cylinder on top that the
funnels have)
Three cracks, precisely.

The clay was pugged. I know about spiral cracks (because of the clay
shrinking in the direction that it
was pugged or wedged ). The clay was balled up to avoid this.

When throwing, I pull all of the clay to the outer rim of the bat, and pull
in. There is no bottom.
The wall thickness is uniform. They are not extremely thick or thin. There
is a hole approximately
a quarter of an inch on top.

So, what's the deal with the cracks?
If any of you have suggestions, I would greatly appreciate them !

Thanks,
Sandra Gekosky
(who wanted to sell bird houses at two craftfairs , the second week of
Sept.)