A slip is a suspension of ceramic materials in water. The term is used in at least 3 different ways.
1. Slips are used as a "glue" to help bond together two pieces of leather-hard clay such as when attaching a handle to a pitcher or mug. In this case the slip can be as thin as water or as thick as whipping cream and is the same composition as the leather-hard pieces on which it is being used.
2. Slips can also be suspensions of clay and sometimes other materials in water which are brushed onto the surface of a pot to give a different color to the surface. When metal oxides or ceramic stains along with a melting aid called a flux have been added for the purpose of decorating the surface of a pot, the term engobe is sometimes used; however it is falling into disuse in favor of the word slip.
3. The third way the word slip is used is in slip casting. In this case the suspension of ceramic materials is poured into a plaster mold. The water is absorbed into the mold and the clay is deposited on the surface of the mold. When the mold is opened a clay casting of the mold shape is obtained. See the section on slip casting for more information.