I cast about 6 or so solid skulls, painted them, removed a few teeth at random,
placed them and then went for the hollow ones.

A couple of elastic bands held the split together then it was an operation to pour enough
fast cast resin to fill about a quarter of the mould the I just stood there with my thumb over
the pouring hole and just waved my hand around to spread the resin about the whole thing.

As it turned out, a crude but effective technique.