When I bake polymer clay in convenction oven it gets a black/burned stain at the place where it touches tray.?

Question:I tried it many times and used sculpty polymer clay. This time I used the thermometre to check the temp plus cover the tray with Aluminium foil but still I got the burn marks on the bottom of my bead. And it changes color too.becomes dull/pale

Answers:
Maybe your oven setting is to hot and you are baking it to long. If your oven has a rack in it maybe,you could try on top rack.
Maybe you got , a bad bunch of polymer clay.
I sculptured a head one time ,when I baked it the head burs ted . Ever thing I made with that clay busted . It was a bad batch of clay.
Take it back, if it isn't your oven making it turn dark.
Queen Bee