Back to the alginate and a little more planning with this one. Firstly a made a nice little Sculpey head with no mouth for a replacement face puppet. I made a small wire stand to support him upside-down in a tin-foil lined jar, and made sure the neck was nice and long (as this would be acting as the funnel to pour the plaster into the mould once it was made). Then the alginate was mixed again, firmly but slowly so as to avoid as few lumps and air bubbles as possible, then poured over and into the mould, and tapped to let it settle into all the cracks and crevices:

Turned out much better than I had expected and has encouraged me to perhaps use alginate a bit more in the future, although I think might try and repeat the process with latex to see which mould making process works out the best for me.