The intermediate mould is seen here boxed up and ready for the last part of the plaster jacket to be cast, the port big side. Note the locating natches cut in the previously cast plaster parts.

I have found that the best parting agent for separating old plaster from newly poured plaster is a thin wash of clay slip. Some authorities recommend soft soap. I have found that the extra thickness of the clay slip allows water to penetrate between the parts when trying to take the mould apart. Soak the whole mould in very hot water, and then force more hot water through a mastic gun into the gaps.

Soap might also migrate onto the slip face of production mould parts and prevent the water being absorbed from the clay slip.

The plaster jacket has been successfully taken apart and washed. The natches (dimples and matching knobs) that locate the parts of the mould can be seen. The mould will be needed again so it is worth while being careful over these details.

The silicone rubber mould has been partly cut open to reveal the undamaged plastilene model inside.