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07-12-2010-Breakability: A ClayMate asked about the "breakability" of polymer clay and this was my reply to her.

Not counting trusting glue on wood to withstand the heat of the oven, which broke that little box on there on the left, there are only so many things that cause breakage with polymer clay. This is what I replied to the ClayMate.


Breakability, two things come to mind. Conditioning and heat setting, which I call curing, some call it baking - but there's more ways to heat set clay than just baking it. 

Conditioning: How long does one need to condition clay? 

Take a very small ball of yellow, like the size of a pea. Then the same size ball of blue. Mash them together until you get green. That's how long you should condition polymer clay before using it. Even if it is only one color. The reason for that is because when the clay is packaged, shipped, stored in store rooms, then put out on the retail shelf, the plasticizers settle to the bottom of the block of clay. By thoroughly mixing the clay up we redistribute the plasticizers in with the filler, pigment, and polymer clay. 

One way I condition the clay is to break it up into chunks, like the size of dice, and toss it all into a food processor and give it a whirl.

If the clay isn't old and crumbly like the clay in that bullseye tutorial, after a little while the whirling clay bits will congeal into a ball. Stop the food processor there and take the ball of clay out. It will be warm and elastic. Next I do a taffy pull. Pull the clay and fold it, pull the clay and fold it again. Until I can pull the clay and it won't break off ragged but it will pull spaghetti noodle thin. This video shows me doing the taffy pull to mix two colors together.

Exception to the conditioning rule: Kato clay responds to pressure, I'm told. I don't have much experience with Kato clay so someone else will have to pipe in and tell us about conditioning that clay. 

Heat Setting: or as I call "curing". Some folks have cured their clay by leaving it in the trunk of their car in a hot Texas parking lot, accidentally. So it doesn't take much heat to set polymer clay. Most brands will heat set at 265F/130C, one half hour for 1/4th inch thickness. I have a tendency to cure things in stages, each stage a half hour.

Sleeping Lady PenPal was in and out of the oven I don't know... once for the body, after filing and smoothing and putting on the scalp, again for her TLS hair, again for her "nightie", again maybe for her face make up. Maybe a half dozen times. But each time at the temperature and duration that the manufacturer of the clay suggested. Same went for her bed of flowers, in and out, some flowers were pre-cured and added with a raw clay anchor, then cured again. In and out of the oven. But each time the time and temperature were as the manufacturer specified. 

I know some folks making mini food tend to cut down the time because "the things are so small". 

Problem with that there are chemical changes that do not take place unless the time and temperature are correct. To short change the time or temperature you risk breakage. 

So those two things.. conditioning and heat setting, when done incorrectly, are the leading cause of breakage with finished polymer clay items. 

I'm looking for Garie's link on testing the relative strength of different brands of polymer clay, but his website is as bad as mine. You go in and then get distracted and sidetracked with other links and then you forget what you were there for. Hah!

Hope that helped some and sorry for just getting back to you on this question. You're right... there are no stupid questions and everyone can learn the techniques for polymer clay.

Update: Grace jumped in with information about Kato Clay.

Thought I would jump in on this one.  I've gone to two Clay Carnivals in Vegas with Donna Kato.  The first year I was told just pound the heck out of her clay while in the package (with a rubber mallet).  We still had some issues with crumbling a lot.  Last year Donna said to slice her clay the thickness of the first setting, put it thru the pasta machine and then keep going one notch down and continue to put through pasta machine.  It actually worked pretty good, much better than the first year where I really struggled conditioning it.  Since then she's done a new formula which is supposed to be much easier to handle.  I use Premo but in Vegas classes I use her clay.  


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