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.

Reply to
GaSeku
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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

Reply to
Mud Dawg

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

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Reply to
Bob Masta

make a shrink ruler.

  1. use a plain old wooden ruler.

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

  2. mark off increments as detailed as you like.

  1. 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

steve graber

Reply to
Slgraber

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

Reply to
GaSeku

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

Reply to
GaSeku

Reply to
James Aberle

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