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## variation on clay specific gravity theme

### Mary Klotz on wed 4 feb 98

how about a formula for determining, from a green/dry piece, and from bisque,
how much wet clay went into it? (I have a bowl I really like, there should be
a way I can weigh it, perform a calculation, and then come up with the amount
of wet clay to start with to do a same size piece.)

Mary
foresthrt@aol.com

### Cindy on thu 5 feb 98

Mary,

You don't have to go to that much trouble. Besides, it wouldn't help. Your
throwing style may be to make thinner or thicker pieces. Ask your clay
supplier (or figure out on your own--I don't know how to do this, BTW) how
percentage of shrinkage (12.5% in my case, and that's pretty average for
stoneware). Be sure to measure the width at the lip and also the height of
the bowl. Then experiment. I find I use about 400 grams to make a 6-7"
rounded bowl, if that helps, but of course, my bowls may be thinner than
you like. It doesn't take much experimentation to arrive at an answer to a
question like this. Just dive in.

Earthen Vessels
Custer, SD
USA

> ----------------------------Original message----------------------------
> how about a formula for determining, from a green/dry piece, and from
bisque,
> how much wet clay went into it? (I have a bowl I really like, there
should be
> a way I can weigh it, perform a calculation, and then come up with the
amount
> of wet clay to start with to do a same size piece.)
>
> Mary
> foresthrt@aol.com

### Jim Horvitz on thu 5 feb 98

Mary You can get your answer by working backwards. Weigh a piece when it is
first thrown (wet). Then bisque and fire it . Weigh it (dry) and devide the
results (wet)/(dry). Use this as a factor to determine the amount of wet clay
a finished piece require. Weight of a finished piece times factor equals
weight wet clay needed. This will give you a good approximation. Calculation
for green ware can be done the same way. Jim Horvitz Rancho Mirage Ca.

### Mary Klotz on fri 6 feb 98

>You don't have to go to that much trouble. Besides, it wouldn't help. Your
>throwing style may be to make thinner or thicker pieces. Ask your clay
>supplier (or figure out on your own--I don't know how to do this, BTW) how
>percentage of shrinkage (12.5% in my case, and that's pretty average for
>stoneware). Be sure to measure the width at the lip and also the height of
>the bowl. Then experiment. I find I use about 400 grams to make a 6-7"
>rounded bowl, if that helps

I have a starting point chart that gives approximate amounts of wet clay
needed to make various sorts of thrown pieces, and I've made my own shrinkage
rules on the computer. I thought that if I had a piece I had made, and wanted
to make another like it, there ought to be some way to extrapolate from the
finished or bisque piece how much wet clay is was when it was born. Aware
that not all clays are pugged to the same firmness= have different water
contents, and an extra allowance must be added for trimming, so admittedly it
would be a rough figure, but I'd rather be able to weigh the few finished