Casting is the method used to form liquid pastes, called slips, which are suspensions of ceramic powder in a solvent, generally water. This involves pouring the slip into an empty, porous mould, typically made from plaster, which, through capillary action, absorbs part of the solvent leaving a growing deposit of ceramic particles on the walls of the mould. For "hollow casting", when it is thick enough, the mould is emptied of the excess slip, whereas for "full mould casting", some slip is retained to compensate for the reduction in volume following the absorption of water by the plaster.
The casting time is generally between 20 and 90 minutes. Demoulding is performed with or without a hardening stage. If the casted part is flexible enough, it can be deburred prior to the drying stage which follows.
This procedure helps with complex parts, with thin walls or large dimensions.
In order to increase productivity, pressure casting has been developed, which reduces the cycle by more than 90%. The slip is injected under pressure into the metal or resin porous moulds, which are more resistant than plaster. The reduced water content of the pressure casted parts is favourable to the drying stage.