Print the seashell in white ABS. Get as much of the raft and supports as possible out from the inside -- you don't want that stuff blocking your lights.
Once it's done, paint it with gold or yellow translucent paint. I used two coats of Pebeo Vitriol glass paint which gave it an almost carved-wood look, but any not-too-opaque paint should work.
If you don't have a 3D printer, you can get one printed at Shapeways. The internet is so great.