What are the advantages and disadvantages of latex casting by using Plaster of Paris mould?

The following assumes we are discussing the Slush Casting Method.

The primary advantage of using Plaster of Paris Moulds with casting latex is their porosity.

The latex solids are drawn to the face of the tool quickly, as the water and ammonia soak into the plaster. It is essential to have a DRY plaster mould to do this with.

Once allowed to deposit latex solids for some time, which varies from latex to latex based on their solids content, the remaining mix is poured out.

Grades of latex go from Cheap Moulding Latex > Cream Latex (40-70% solids variation!)

The next advantage of a PoP mould is the speed which latex dries within it. Being fully porous, this allows the latex to dry from "both sides". Also the fact that the water/liquids disperse within the plaster.

The whole mould then becomes a drying surface.

The main disadvantage of PoP moulds is mould longevity. Plaster of Paris is a Beta Plaster. This means the plaster is essentially weaker. Its second main disadvantage is fine details can be lost to the larger particle size and therefore definition.

To combat this try to find a harder plaster, but the balance is fine. Too hard and the porosity drops. In the UK Herculite 2 is a good balance, but Plaster of Paris (Fine Casting Plaster by British Gypsum) is cheap and readily available -ebay or a web search for british gypsum fine casting or herculite 2 will see you right!

Summary

Advantages

• Porosity
• Value
• availability

Disadvantages

• Shorter Mould Life
• Potential Loss of Detail