A two part slip cast mold made of plaster allows for the creation of more complex cast forms than are possible with a one piece mold.

Ideal objects for slip casting should be relatively simple and do not have deep undercuts

Mold clay is used to build up a base around the object to be cast. This clay should not be mixed back in with clay to be used in kiln fired ceramics since plaster inclusions in the clay may cause the fired clay to explode. The build up should meet the half way point of the object, or the parting line. This is the infinitely thin plane that is perpendicular to the tangent point between the divide of undercuts.

Cottle boards are used to support the outer edges of the mold clay and to create a square boundary for the plaster to be poured into.