If the staff didn't need such a huge ball I'd consider resin casting it, but hollow is best in this case, so I bought a wooden pole and two part acrylic sphere. Using the dremel I drilled a hole in the bottom of the sphere for the pole and any electronics to fit into.
I did a lot of testers on smaller spheres with combinations of sanding and glass paints to get a nice glow, but in the end I've decided to leave it un-sanded and glass paint the inside in layers.
Bonus of this is that the paint can't be scratched off, it'll be protected inside the sphere and the outside will have a perfectly smooth surface.
Things I learnt from the testers:
-Glass paint crazes (bubbles up) if you try to paint another layer on later no matter how long you leave it to dry, so get it right first time. Bubbling is worst on areas of thicker paint.
-Though sanding the acrylic looks rough and cloudy, glass paint fills in the ruts and can make it clear and transparent again (defeating the point), so best to sand inside, paint outside if you want to keep it opaque.
-Glass paint can be cleaned off with white spirit, but this also clouds up the acrylic plastic, damaging the surface, BEWARE. The surfacing effect of glass paint mentioned above can also make this damage transparent again, but that's when you realise there are white spirit fingerprints on the outside too...