I have never tried casting anything in plaster until now, using the large nylon salad bowl my mother gave me 20 years ago as my modelling form.
Playdough walls to define the shape and everything covered liberally with Vaseline. I poured the plaster and allowed it to thicken and spooned out the excess. I made two castings and after finishing them to a smooth polished surface, I glued them together.
As I failed to realise how fragile it was, ordinary Plaster of Paris without an armature, it broke . . .
Now I am starting again but bigger and better. I have acquired a large wok and a bag of terracotta coloured sculpture plaster which not only is very tough but also has iron inclusions which will gradually rust on the surface.