I've never burned Polymer clay but just baking it according to the
manufactuer's instructions gives off terrible fumes which you have
to vent. Absolutely, do not go there.
Grace, I agree that one should "not go there," but it sounds to me
like you need to check the oven you're using to bake polymer clay.
When the temperature is correct according to manufacturers'
instructions, polymer clay gives off little in the way of fumes (it
still should be vented). I use a second-hand toaster oven in which I
set a separately-purchased, stand-up oven thermometer, to bake
polymer clay. In order to stay at about 265-275 degrees, I have to
set the oven dial at 350 degrees, which gives you an idea of the oven