Since the eighteenth century the new plaster of Paris appeared, it extreme changes the traditional techniques of pottery.
Plaster mold used in slip casting allows mass the production of form in uniform consistency.
Four types of molds in common 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 mold. A film of clay is built up when the plaster mold absorbed the water of slip. As the desired thickness is achieved, the excess clay slip is poured out. The clay coating inside the mold will be ready to remove when it is leather hard.
Slip is a mix of clay, water, and a 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.