I hate that question. Not because it's a difficult question to answer — but because I know the heartbreak reflected in having to ask it. I've had my share of burned pieces over the years, and some of them were just devastating. I'm not usually overly emotional, but I've definitely shed some tears over ruined work. And I know that kind of disappointment can be enough to keep a new clayer from ever touching the stuff again.
Plus, maybe it's like the Murphy's Law of Polymer Clay, but it seems to me that more work you put into a project, the more likely you are to run into problems baking it. One clay artist calls those burned pieces her "sacrifice to the clay gods." (The quote stuck with me, but not the name of the artist I got it from — please leave a comment if you know.)
In the interest of keeping those sacrifices to a minimum, here's a few tips on keeping your polymer clay pieces from burning:
Get a good oven thermometer. I've never had a toaster oven where the temperature dial was accurate. I bought a Taylor brand oven thermometer I really like on Amazon for $12 and leave it in my toaster oven at all times. Other oven thermometers would probably work, too, but I noticed the cheap-o one I had was slower to register temperature changes and harder to read accurately.
It seems worth mentioning here that burning clay is a temperature thing, not a time thing. If the oven temperature goes above the recommended temperature for that brand of clay, it will start to burn. However, baking for longer than the minimum time should be fine.This is nice for complicated pieces, since it allows you to bake in stages. Plus many folks feel that clay that's baked longer is stronger. I've read that some brands' lighter colors may start to brown slightly (but not burn) with longer/multiple bake times — see more on solutions for that below.
Preheat the oven. I'm not sure "preheat" is the right word, actually. In my toaster oven, the temperature soars to over 400 degrees before settling on the right temperature after about 10 minutes. So maybe "pre-cool-down" would be more accurate? Regardless, be sure to let your oven get to the right temperature before putting your polymer clay in. If I were to put my clay in as soon as I turned my oven on, it would definitely scorch.
Consider changing ovens (maybe). Some of the most reliable toaster ovens I've had were $5 or less at a garage sale, so I certainly don't think expensive ovens are necessary. But if you run some tests with your toaster oven and find that it just can't keep a consistent temperature, it may be time to try a different one.
Some folks love their convection toaster ovens, saying those are better at keeping a consistent temperature throughout the oven. I tried a couple of different convection ovens from JC Penney's Cooks line, and I couldn't get the convection oven settings to work on either. It wouldn't stay at clay temperature no matter what I tried. I was able to get the toaster oven portion on the same ovens to work, though, so all wasn't lost (and they're big, so they have plenty of room for baking lots of stuff). Still, not all convection ovens are created equal. Do some research and get some recommendations before investing in anything.
Be careful with certain clay brands and colors. Some polymer clay brands are just more susceptible to getting toasted. Original Sculpey white and some lighter colors of Sculpey III are especially bad about this, though I generally wouldn't recommend those brands anyway since they tend to be more brittle after baking. But you may run into the same problem with better brands' whites or translucents. If so, try taking some extra precautions (such as polyfill or tenting) when baking.
Try polyfill and/or tenting. If I have a tall sculpture with a piece that's a little closer to the heating element than I like, I'll often use polyfill for some extra protection. Polyfill's good for preventing the slight browning of lighter clays.
Another method many clayers swear by is tenting with aluminum foil. I've only done this a few time, so I'll refer you to Glass Attic's baking page for some tips on tenting and otherwise enclosing your clay while baking.
If all else fails, paint. Sometimes a browned piece can be salvaged with a little acrylic paint. At least try it before you throw that masterpiece away!
While the occasional "mis-fire" may still occur, I hope these tips will help keep those heartbreaking burned pieces few and far between.
I'd love to hear your tips, too. Just leave a comment below.