Unless I’m in a hurry, I’ve typically put polymer clay in a cold oven, baked it for 30 minutes and let it cool in the oven. The main reason I’ve been using this seemingly gentler method is because I read that it reduces plaquing. It does seems like less of a shock to the clay, but do I need to rethink?
Plaquing is basically flat bubbles in the clay. It looks pretty bad unless you’re trying to make faux granite or jade. Plaquing happens in opaque clays, too, it’s just not as easy to see.
The benefit of preheating is that you know what the temperature is and can come closer to manufacturer’s recommendations. Polymer clays need certain temperatures and durations to fuse. If you don’t meet those requirements, you can run into problems, such as crumbling and breaking.
The downside of preheating is you have to pay more attention. You have to be careful to not burn yourself when putting clay into a hot oven. Hot clay is very pliable, so you have to be careful when taking it out of the oven, too.
I decided to test preheating versus a cold oven using translucent clay to see if it made any difference with plaquing. I used five different brands: Fimo, Kato, Premo, Pardo and Cernit. I followed the temperature recommendations for each and covered them with tin foil to bake for 30 minutes. I gave 5 more minutes of baking time to those going into a cold oven.
After seeing the results, I decided to do two more tests using 20 and 45 minutes in the oven on the two clays that showed the most plaquing: Kato and Fimo.
This test was to learn about preheating and plaquing, not to create nice-looking pieces of translucent polymer clay. Thank goodness, because some of these look pretty bad. The longer I baked Fimo, the more orange it got. Kato and Premo yellowed quite a bit.
With Pardo, there was no plaquing with either method, just some very small bubbles that I probably made. I’m so impressed that Pardo is almost transparent! I’ve only used it once before and found it very crumbly and difficult to condition. This time I conditioned it by hand before putting it through the pasta machine just to make a flat, uniform sheet. It came out of the oven with kind of a sticky film on it, so I rubbed that off with a paper towel and then buffed it. Wow!
Cernit had no plaquing in the cold oven method, but had some in the preheated method. This was my first time using Cernit and the clay I had was very soft. I conditioned it with the pasta machine and when it baked, it had hundreds of tiny bubbles in it. I thought I might have better results if I conditioned it by hand, but it made no difference.
Premo didn’t plaque with either method.
Kato and Fimo plaqued regardless of method. Some of the plaques near the surface caused bumps in the clay.
CONCLUSION
What I’d conclude is that putting polymer clay in a cold oven and letting it gently heat up and cool down doesn’t seem to make a difference in plaquing, except possibly with Cernit. It’s probably best to preheat to be sure of the oven temperature.
P.S. I bought all these products myself and received nothing from the manufacturers.
Polymer Clay Journey 
Hi, after reading your post on baking polymer clay, I’m a bit confused. Here you say: “Cernit had no plaquing in the cold oven method, but had some in the preheated method. This was my first time using Cernit and the clay I had was very soft. I conditioned it with the pasta machine and when it baked, it had hundreds of tiny bubbles in it. I thought I might have better results if I conditioned it by hand, but it made no difference.”
And then later you said: “What I’d conclude is that putting polymer clay in a cold oven and letting it gently heat up and cool down doesn’t seem to make a difference in plaquing, except possibly with Cernit. It’s probably best to preheat to be sure of the oven temperature.”
So, which is better? A cold oven or preheated oven for baking Cernit?
Thank you.
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That is a bit confusing! What I was trying to say was that Cernit had no plaquing in the cold oven method, so that’s what I recommend for it.
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