Re: 3-d Sculpture Modeling Programs - Sculptris
I haven't burnt out PLA myself, but I've talked about it with people who have. If you're doing ceramic shell casting, you can get it a lot hotter than plaster-based investments can handle, which should be good for PLA. You might try a blast with straight oxygen to combust any remaining unburned ash in the mold.
I've been doing jewelry-scale castings from 3D-printed photo-catalyzed resin, though; that works pretty well. What's the new material you're using that burns out better? How do you eliminate those striations from the printing process?