1 Pottery Plaster specifically) is the preferred mold material as it provides the best combination of detail retention, strength and absorbability. Less water results in far less shrinkage, greater strength, much faster set-up times and less wetting and thus drying time for the plaster molds.
Rather, they are a precise formulation of water, clay and a deflocculant which acts to reduce the amount of water required to maintain the liquid, pourable state and to keep the clay particles suspended in the water and the mix homogeneous. Modern slip clays are not just watered-down clays as might be used for decoration perhaps with colorants added, as an underglaze for example.
