When the sculpt is ready to be moulded, first thing to do is to put up a clay wall.
It is important to remember that the head cast is firm, so don't put the wall to far back, since it will create an undercut and the mould will stick to the cast. You don't want this to happen!
The wall is put up about 2 cm from the edge of the sculpted mask, this will work as touch down when putting it back together, along with the eyes.
To strengthen the wall, I cover the back of the head with cling film and then putting plaster bandage over it. This makes the clay wall strong enough to hold the plaster when moulding.
Make the wall smooth and put some Vaseline on all of the exposed plaster, to prevent them from sticking to each other.
Then lay the cast down and cover all exposed areas with plastic to avoid it getting to messy.
Mix the first layer of plaster really thin, like a single cream, carefully covering the whole sculpt, this will pick up all of the detail.
Then continue with several thicker layers until it is thick enough, about 5-7 cm all over.
Since the mould will be placed in the bottom, with the cast pressed down into it when making the latex foam, the top of it needs to be flat. To make it flat I file it down with a surform when the plaster is starting to set, but still is quite soft.
Then the mould is done and I leave it to set over night.