Since the eighteenth century the new plaster of Paris is appeared, it extreme changes the tradition techniques of pottery.
Plaster mould used in slip casting allow mass the production of form in uniform consistency.
Four type of molds in commom as following,
3/ With Countermold
4/ With Suspended Countermold
Slip casting is a way of making ceramic in which a liquid form of clay is powered into a hollow mould. A film of clay is built up when the plaster mould absorbed the water of slip. As the desired thickness is achieved, the excess clay slip is poured out. The clay coating inside the mould will be ready to remove when it is leather hard.
Slip is mix of clay, water and small amount of deflocculates. The addition of max. or less than 1% deflocculates (such as sodium silicate and soda ash) of dry clay will reduce considerably the amount of water needed.