Hello, I am not the expert.
I read this thread posted here
http://www.statueforum.com/showthread.php?t=79360 (well, this very thread it looks like)
and decided to try boil. Works great even though a sculpey rep tried to advs against it. Said temp not high enough.
but my roaster goes up to 450F & I pretty followed the instructions in the thread above. I also put in the work before it got super hot.
You might want to contact the person who orignally started they thread as they might have more experience.
You might also want to experiment w/a trial piece? Do an extra head and see what happs?
Good luck looking forward to seeing your sculpt.