David Berg on wed 20 dec 06
Art = science = math.
The 12.5% shrinkage should be calculated from the wet clay
not from the fired piece. So, assuming 12.5% shrinkage then
use the formula below in order to come up with an approximately
10" plate:
wet clay size = 100% or 1.00
100%  12.5% shrinkage = 87.5% final fired size
So, the glaze fired size = 87.5% of the wet clay size or 0.875
Calculate the wet diameter one needs to end up with 0.875
(87.5%) the size of the wet diameter.
10" / 0.875 = 11.5" thrown wet diameter
So, anyway you were closer than the first calculation and it is
really just in the realm of detail now because your 11.25" wet
diameter plate would be pretty darn close to 10" also  i.e.
just short of the mark at approximately 9.84375". But that
is just a rough estimation. ;)
David Berg
dberg2@comcast.net
http://bergstoneware.com/
On Dec 20, 2006, at 5:01 AM, tinkerbellesarah wrote:
> Ummm... I think the shrinkage example you gave is incorrect. A 12.5"
> plate shrinking to 10" is a 20% shrinkage (12.510=2.5,
> 2.5/12.5=20%)... if you want a 10" plate and have 12.5% shrinkage then
> throw it 11.25"
>
> Sarah in Sitka
> nothing witty to say tonight
tinkerbellesarah on fri 22 dec 06
Yeah, I realized I did that right after I shut the computer down. It
was late at night and my husband was talking to me at the same time so
I got addled... terribly ironic, having to be the correcter and all,
much like the one who typoed in her misspelling bit... we're all
human. =3D)sarah in sitka
 In clayart@yahoogroups.com, David Berg wrote:
>
> Art =3D science =3D math.
>
> The 12.5% shrinkage should be calculated from the wet clay
> not from the fired piece. So, assuming 12.5% shrinkage then
> use the formula below in order to come up with an approximately
> 10" plate:
>
> wet clay size =3D 100% or 1.00
> 100%  12.5% shrinkage =3D 87.5% final fired size
> So, the glaze fired size =3D 87.5% of the wet clay size or 0.875
>
> Calculate the wet diameter one needs to end up with 0.875
> (87.5%) the size of the wet diameter.
>
> 10" / 0.875 =3D 11.5" thrown wet diameter
>
> So, anyway you were closer than the first calculation and it is
> really just in the realm of detail now because your 11.25" wet
> diameter plate would be pretty darn close to 10" also  i.e.
> just short of the mark at approximately 9.84375". But that
> is just a rough estimation. ;)
>
> David Berg
> dberg2@...
> http://bergstoneware.com/
>
> On Dec 20, 2006, at 5:01 AM, tinkerbellesarah wrote:
>
> > Ummm... I think the shrinkage example you gave is incorrect. A 12.5"
> > plate shrinking to 10" is a 20% shrinkage (12.510=3D2.5,
> > 2.5/12.5=3D20%)... if you want a 10" plate and have 12.5% shrinkage the=
n
> > throw it 11.25"
> >
> > Sarah in Sitka
> > nothing witty to say tonight
>
>
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