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## figuring clay shrinkage for the mathmatically challenged

### David Hendley on wed 26 nov 03

If doing math problems is not your favorite activity, here is how to
accurately size your pottery without ever doing a single math
operation:

1. Buy a plastic ruler with raised lines for the scale.
2. Make a slab of clay the same size as the ruler, about 3/8" thick.
3. Press the ruler into the slab.
4. Repeat 2 & 3.
5. When dry, bisque fire the slabs.
6. Glaze fire one slab.

You now have shrink rules specifically for your claybody and your
firing temperatures.
If you need to match a fired piece or a certain opening, just measure
the piece with the glaze-fired shrink rule. Whatever it measures
is how big to make the new piece. Of course, the number on
your shrink rule will be backwards, but it is not to hard to figure
that out. If, for example, you measure a plate using the shrink
rule and it is 7", you will set your calipers at 7", using a standard
ruler as a guide.

If your assignment is to make a 10 1/2" diameter plate, just hold
your shrink rule next to a ruler and see what it reads at 10 1/2"
on the standard ruler.

If you break a lid after bisque firing, get out your bisque-fired
shrink rule, measure the opening of the bisque-fired pot, and you
will know how big to make a replacement lid.

David Hendley
david@farmpots.com
http://www.farmpots.com

### Marianne Lombardo on wed 26 nov 03

David,

Thanks for the post on making the clay shrink rulers! What a good idea, and
so easy. Since I use 3 different claybodies, I'm going to make a set for
each one, and carve the name of the claybody into the ruler as well. Good
post!

Marianne Lombardo

### John K Dellow on thu 27 nov 03

David ,
very interesting way to go about a shrinkage ruler. Not what I was
taught but workable.
I was taught to do the math's and work out the shrinkage factor and make
up a wooden ( I use bamboo)
ruler. If I am making a 12 in tall pot then I set the gauge at 12 on
the ruler. In actuality I have been
metric for 25 years , but still call my terra-cotta pot in inches .i.e.
strawberry pots are
7 ,9,11,13,15 & 18 inches :). Old dogs and new tricks :).
John

David Hendley wrote:

>If doing math problems is not your favorite activity, here is how to
>accurately size your pottery without ever doing a single math
>operation:
>
>1. Buy a plastic ruler with raised lines for the scale.
>2. Make a slab of clay the same size as the ruler, about 3/8" thick.
>3. Press the ruler into the slab.
>4. Repeat 2 & 3.
>5. When dry, bisque fire the slabs.
>6. Glaze fire one slab.
>
>You now have shrink rules specifically for your claybody and your
>firing temperatures.
>If you need to match a fired piece or a certain opening, just measure
>the piece with the glaze-fired shrink rule. Whatever it measures
>is how big to make the new piece. Of course, the number on
>your shrink rule will be backwards, but it is not to hard to figure
>that out. If, for example, you measure a plate using the shrink
>rule and it is 7", you will set your calipers at 7", using a standard
>ruler as a guide.
>
>If your assignment is to make a 10 1/2" diameter plate, just hold
>your shrink rule next to a ruler and see what it reads at 10 1/2"
>on the standard ruler.
>
>If you break a lid after bisque firing, get out your bisque-fired
>shrink rule, measure the opening of the bisque-fired pot, and you
>will know how big to make a replacement lid.
>
>David Hendley
>david@farmpots.com
>http://www.farmpots.com
>
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--

John Dellow "the flower pot man"
From the land down under