Slip Casting Questions and Answers

Answer: A

Correct answer: drawing water out of the slip by capillary suction

The fine pores of the plaster exert a suction that pulls water out of the slip at the mould face, leaving the ceramic particles behind as a consolidating layer. Nothing is heated and nothing reacts; the driving force is capillarity, and the process stops when the plaster is saturated, which is why moulds must be dried between casts.

Answer: B

Correct answer: has fine pores and absorbs water readily

Set plaster is a mass of interlocking gypsum crystals with a fine, connected pore structure, which gives it both the capillary suction to draw water and the capacity to hold what it draws. It is also cheap, easily cast to shape from a model, and slightly soluble, which helps release. It is certainly not hard, and its softness is why a mould lasts only a hundred casts or so.

Answer: C

Both are true and the reason gives the necessity: a saturated mould draws water only slowly, so the cast builds unevenly and the production rate falls, which is why moulds are cycled through a drying room in a pottery.

Answer: D

Once the plaster approaches saturation its capillary suction falls away and casting slows markedly. Production potteries hold several sets of moulds so that some are drying while others are in use. Mould stock rather than mould quality often limits output.

Answer: A

Particles carrying a like charge repel one another and the suspension flows freely even when heavily loaded. A high solids content means less water to remove, which speeds casting and reduces drying shrinkage. Water removed later has to be paid for in kiln time and in cracking risk.

Answer: B

Both are true and the reason gives the mechanism: dispersion allows the same solids to be carried in less water, so the mould has less liquid to absorb for each millimetre of cast it builds. Faster casting also means less time for the slip to settle in the mould.

Answer: C

They exchange sodium for calcium on the clay surfaces and raise the surface charge, which disperses the particles. Modern slips often use polyacrylate dispersants instead, which give finer control over the same effect. Their dose is far less sensitive to small errors in weighing.

Answer: D

Beyond an optimum the excess electrolyte compresses the double layer and the slip begins to flocculate again. The dose is found by titrating and plotting viscosity against addition rather than by adding freely. The curve has a clear minimum that the operator works to.

Answer: A

Thirty-five per cent of 20 kilograms is 7 kilograms of water. Every kilogram of that water must be absorbed by the mould or evaporated later, which is why raising the solids content matters so much. Every kilogram of water is a kilogram the mould must absorb.

Answer: B

The growing cast itself resists the flow of water, so each additional millimetre takes longer than the one before. Doubling the thickness therefore requires roughly four times the time. The relationship is derived from Darcy flow through the growing cast.