Preventing Polymer Clay from Cracking

Proper Design and Curing Will Help

Why Do My Polymer Clay Pieces Crack So Easily?

There are several reasons that cured polymer clay could crack. Here are some tips that should help.

I have a question regarding my pieces cracking after being complete. I bake the Sculpey in a toaster oven and afterwards they seem fine but when I wear the pieces they seem to break with minimal stress.

Like when I am wearing the piece and happen to place my purse (a small purse) strap over the piece. It seems like it cracks and breaks easier than it should.

What am I doing wrong?

Sue

It’s difficult for me to say without actually seeing the pieces.

Perhaps they are too thin and have contours opposed to the surface they are pinned to or placed against. Put those conditions together and only minimal pressure would be required to crack them.

As an analogy, imagine a very thin dome-shaped piece of glass laid on a flat surface. Press down on the dome and the glass fractures.

Imagine an equally thin flat piece of glass laid on a flat surface. Apply the same amount of pressure and the glass does not break.

All that said, I should tell you that cured polymer clay is quite brittle.

Forms like beads and round shapes for figures like my Snow People are quite durable. However the scarf on my snowman and the strands of hair on my snow-lady could easily be broken.

I have two other thoughts. Are you sure you are not over-baking the clay?

That would make it even more brittle. Do you allow your pieces to cool before touching or moving them?

You can either let them cool in the oven with the door open and heat off or carefully remove the pan and set it on a wire rack.

Cured polymer clay is at its most vulnerable while it is cooling.

I hope these ideas help.

Hi Eileen,

I have been reading several books and just started experimenting with polymer clay. One of the authors pointed out that the temperature must be exactly what the manufacturer says it should be. She recommended buying an oven thermometer to get an accurate reading and not relying on the oven for that. It the temperature is not right, the material will not fuse together well and will break easy. The only risk of over baking is that the clay might release fumes that might be harmful.

From my first experience I found that even though my convection oven (counter small oven) was set to 300 degrees, the thermometer only marked 250. When I adjusted the oven to 350, then the thermometer reached 300. The clay did release some smoke when it got the right temperature (which I also read it was normal), but next time I will bake outside just to be on the safe side. Anyway, I hope this helps.

Thanks for such a wonderful site, very inspiring.

Glenda Munguia
Beautiful Pictures by Glenda