Slip Casting Questions and Answers

Answer: A

Flocculated particles trap water in an open structure, so the cast is porous and the surface poor. Correcting it means adjusting the deflocculant rather than adding more water. Diagnosing the cause matters more than treating the symptom here.

Answer: B

Both are true and the reason gives the objection: the slip becomes more fluid but casts even more slowly and shrinks more on drying, so the underlying dispersion problem has to be addressed instead. Water dilutes the slip without dispersing anything.

Answer: C

The first two are correct. The third is the classic wrong remedy, since water thins the slip while leaving the flocculation untouched and makes both casting and drying worse. More water means a longer cast and a greater drying shrinkage.

Answer: D

Correct answer: True

A higher solids content means less water to remove for the same wall thickness, so the cast builds faster. The proviso matters: it is only achievable with good deflocculation, since without it a concentrated slip becomes too viscous to pour or to fill fine detail. Raising solids and holding viscosity down is the whole purpose of the deflocculant.

Answer: A

Turbulent or interrupted filling leaves marks where the slip surface paused against the mould. Filling steadily from a single point and avoiding air entrainment are the usual preventions. The defect shows most clearly on a glazed vertical surface.

Answer: B

Each bubble becomes a void in the wall and a blemish on the surface. Slips are therefore aged and often de-aired under vacuum before use, and pouring is arranged to avoid splashing them in. A de-aired slip also casts a little faster and more evenly.

Answer: C

Ageing allows entrained air to escape, lets the deflocculant act fully and stabilises the rheology. Freshly made slip commonly behaves differently from the same slip a day later. Production slips are held in agitated tanks for this reason.

Answer: D

Both are true and the reason gives both benefits: the rheology becomes stable and reproducible, so the casting time needed for a given wall thickness stops drifting from one batch to the next. Consistency of casting time is what a production line depends on.

Answer: A

Correct answer: allow it to firm up and shrink away from the mould

After draining, the plaster continues to draw water and the cast stiffens and contracts slightly, pulling clear of the mould face. Releasing it too soon means handling a piece that is still soft enough to distort or tear; leaving it too long lets it shrink onto any undercut and stick. The dwell is judged by experience for each shape.

Answer: B

It is still soft and would distort or tear, and it has not yet shrunk away from the mould face. A period of firming in the mould is part of the normal cycle rather than a delay. The firming time is set by the section thickness of the piece.