Calculating shrinkage

Is there a fairly simple, but most importantly, very accurate way to figure
shrinkage? I would love to know how to be sure the finished piece would fit,
say a ring for large water urns, spigots, lamp kits, etc.
Thanks for putting up with all my newbie questions.

Thanks Fiona.

There are at least two ways to calculate shrinkage. The first is to buy a
shrink ruler, which has four different shrinkage factors already printed on
the ruler. Ask your supplier what the shrinkage factor is for your clay and
then use that number (i.e. 12%) on the shrink ruler. The other way is to
cut a ruler size slab from the clay body you use. Using a ruler, make your
marks on the piece of claythat correspond to the markings on your ruler or
tape measure. Then you go through the normal firing procedures that you
normally use. The clay will have shrunk but all of your markings are
proportional. Take your original ruler you used as a guide. Lets say you now
want an 8" bowl. Take your tape measure and see where 8" falls on your clay
ruler. Let's say it falls at 9 3/4" on your clay ruler. You now know that
to get an 8" bowl you must throw something approximately 9 3/4" to end up
with 8". Have I confused you enough? Steve in Tampa, FL, USA

"GaSeku" wrote in message
...
Is there a fairly simple, but most importantly, very accurate way to
figure
shrinkage? I would love to know how to be sure the finished piece would
fit,
say a ring for large water urns, spigots, lamp kits, etc.
Thanks for putting up with all my newbie questions.

On 04 Jul 2003 16:47:34 GMT, (GaSeku) wrote:

Is there a fairly simple, but most importantly, very accurate way to figure
shrinkage? I would love to know how to be sure the finished piece would fit,
say a ring for large water urns, spigots, lamp kits, etc.
Thanks for putting up with all my newbie questions.

I'm also a newbie, but the shrinkage issue is the first thing I had
to deal with. The project that got me into clay was to
make ceramic flanges for odd-sized shower faucets, and they
had to be the correct length to fit.

What I noticed is that my clay shrinks a certain amount in
getting to bone dry, but then there is no more shrinkage
until it gets near maturity. I tried this on a "wide-range
stoneware" body, and briefly on a stoneware body and on
some native clay.

So my solution was to make the pieces a little too big
so that when bone dry I would have to remove a small
amount by sanding (or whatever) to get them to the
exact size needed. The big problem was finding a
glaze that would fit on a non-mature body. I ended
up with Behren's "Simple Colemanite Glazes" and
just kept moving up the cone ranges until I got one
to work, at cone 2 on the wide-range stoneware.

This method also works well for drawer pulls with
threads right in the clay to receive the screws to
hold them on to the drawer... no glued-in inserts
needed. I'm still experimenting with the easiest/
best way to do it, but one way that works well
is to drill bone-dry clay to just fit the screw, then
coat the screw with slip and let it dry in place.
(I applied a light layer of wax to the screw first.)
When that dries, you carefully unscrew the screw
and fire. (I bisque to C04 and glaze to C2.)



Bob Masta
tech(AT)daqarta(DOT)com

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com

make a shrink ruler.

1. use a plain old wooden ruler.

2. cut a slab of clay to the size of the ruler.

3. mark off increments as detailed as you like.

4. fire the clay "ruler". and glue it to the back of the "real" ruler.

on one side you'll see the starting size, on the other you'll see the finished
size. you can make judgements from there based on what you want to make. .

i have several rulers in my workshop for different clays.

see ya

steve




Subject: Calculating shrinkage
From: (GaSeku)
Date: 7/4/2003 9:47 AM Pacific Daylight Time
Message-id:

Is there a fairly simple, but most importantly, very accurate way to figure
shrinkage? I would love to know how to be sure the finished piece would fit,
say a ring for large water urns, spigots, lamp kits, etc.
Thanks for putting up with all my newbie questions.








steve graber

This is great info. Thanks so much! I am so grateful to all who have answered
my question. You are great people!

Steve,
How clever! Thanks for the great tip!
Gaye

I love it when people make things nice and simple and also solve the
question at hand.......very good....from Jim in Jersey

psci_kw wrote:

"Mud Dawg" wrote in message
om...


There are at least two ways to calculate shrinkage. The first is to buy a
shrink ruler, which has four different shrinkage factors already printed


on


the ruler. Ask your supplier what the shrinkage factor is for your clay


and


then use that number (i.e. 12%) on the shrink ruler. The other way is to
cut a ruler size slab from the clay body you use. Using a ruler, make your
marks on the piece of claythat correspond to the markings on your ruler or
tape measure. Then you go through the normal firing procedures that you
normally use. The clay will have shrunk but all of your markings are
proportional. Take your original ruler you used as a guide. Lets say you


now


want an 8" bowl. Take your tape measure and see where 8" falls on your


clay


ruler. Let's say it falls at 9 3/4" on your clay ruler. You now know that
to get an 8" bowl you must throw something approximately 9 3/4" to end up
with 8". Have I confused you enough? Steve in Tampa, FL, USA

"GaSeku" wrote in message
...


Is there a fairly simple, but most importantly, very accurate way to


figure


shrinkage? I would love to know how to be sure the finished piece would


fit,


say a ring for large water urns, spigots, lamp kits, etc.
Thanks for putting up with all my newbie questions.





Steve, the idea of making a ruler out of the same clay is pure genius!
Can I throw my calculator away now ? g
Now all I have to do is figure out how to make it flexible :)
Wayne
Key West

(GaSeku) wrote in message ...
Steve,
How clever! Thanks for the great tip!
Gaye


Gaye,

What I have done is as follows:

Mark a strip of the relevant clay
at exactly 300mm between two
points.

Fire the clay in the usual way.

After firing, measure between the two
marks. Scan a 300mm rule into Photo-
shop, or similar and the reduce it with
a scaling tool to the fired measurement.
You can then print out your 'shrinkage rule'
and have as many copies as you wish!,
and flexible too.

If you work on the wheel, you may wish to
create your clay strip by cutting a 25mm
band from the top of a thown vessel and
flattening the strip out after it has dried for
a while (pre leather hard). This will much
better reflect the slightly higher moisture
content of thrown pots and allows for
'stetch' in the clay.

Hope what ever you do works for you.

Mike DOnaldson
nzpottery.20m.com