For hollow pieces, such as vases, that will be cast later, the filter cake has to be processed into a casting slip in a large mixer. Water and a "condenser" are added to the mix. The mass must have certain attributes before it can be slowly poured into rotating working moulds. The plaster used in the moulds draws moisture from the mass, so that an increasingly hardened layer forms on the walls of the mould. Careful attention is then paid to make sure that, as soon as the desired strength of the body is attained, the remaining liquid mass is removed from the mould. After that, the cast object begins to dry somewhat, initially in the mould. That way, the shrinkage process is minimised and the mould releases itself from the body. At just the right moment, the working mould is opened and the cast object is removed from the mould.