Don't know... Looks a little like white/transparent plastic... I think clear resin with a drop of electric blue casted in a pressure pot, or whatever make the resin without bubbles, should do the trick on a accurate replica... About the stuff inside, it could work, but some crumpled foils of cellophane mixed with some seran wrap would work even better I think (strictly a personal opinion)
No, no, I was saying that the pictured skull is clear and filled with the irridescent stuff. I don't mean to confuse.
