Practice question · Sort into groups
Sort each situation by whether a release agent is usually NEEDED or NOT.
Groups: Release agent needed · Usually not needed
- Plaster mould over damp clay
- Plaster against plaster with no barrier
- Resin cast in a silicone mould
- Plaster over a porous unsealed original
- Silicone against a sealed non-porous surface
- Plaster cast against a plaster mould
Hints
- Ask whether the two materials will bond or key into one another.
- Two identical materials set against each other is the classic failure.
Show the answer
Release agent needed: Plaster cast against a plaster mould, Plaster against plaster with no barrier, Plaster over a porous unsealed original
Usually not needed: Plaster mould over damp clay, Silicone against a sealed non-porous surface, Resin cast in a silicone mould
Why
Plaster against plaster is the failure everyone commits once: two chemically identical pieces set against each other bond permanently, and the mould and the cast become a single lump. Soft soap or shellac and wax exist entirely to prevent it.
Practise Moulds II: Materials and Procedure
The app has 5 more questions on this lesson, and keeps your place in the course. Sculpture I is free to start.
More questions on Moulds II: Materials and Procedure
- Why is plaster sifted into water and left to stand before mixing? Select every true statement about the…
- The setting of plaster is exothermic, so a setting block becomes noticeably warm.
- Complete the account of plaster and moulding.
- Plaster moulding requires careful mechanical preparation rather than relying on chemical separation alone.…
- Roughly how many parts of water per 100 parts of plaster does a typical pottery plaster use, by weight?
- Arrange the steps of mixing and pouring plaster in order.
- Roughly how many minutes of working time does a typical plaster mix allow between pouring the mix and it…