02.01 How to Slip Cast

Slip is clay suspended in water. Plaster absorbs water. When slip is poured into a plaster mold, the plaster sucks the water out of the slip that is closest to the plaster. This slip starts to become more dense and transforms into a clay shell. There is still wet slip inside the shell. After a specified amount of time when the shell is at the desired thickness, the remaining wet slip is poured out of the mold for use in another slip casting. The clay shell is still very moist and soft. Molds can be flipped upside down to allow all excess slip to drain out. After waiting for the shell to dry and harden more, it can be removed from the mold. Then the slip cast cam be cleaned up and or manipulated before firing in a kiln.

Process

1. Secure the pieces of your mold together with large rubber bands and or clamps.
2. Use clay along the seam as needed to fill any large gaps in the mold to prevent slip from pouring out. The slip will lose moisture after touching the plaster and become less fluid so small gaps will be plugged by the slip.
3. Gently pour the slip all the way to the top of the mold to allow all air from the mold cavity to escape.
4. Allow the slip to sit in the mold for a predetermined amount of time, generally 10 - 20 minutes. This will change based on the moisture content of the mold, the size of the mold and mold cavity, the consistency of the casting slip and other variables.
5. Take notes about everything that you do, especially on the early casts. Wright down the time the slip was poured, the time left in the mold, moisture content of mold, how long since previous slip cast pull, how thick the slip walls became, and any other observations.

Example Slip Casting Log Sheet

Tips

• Similarly to preparing paint for spraying, it can be a good idea to pour slip through a screen or sieve to catch any solid particles or debris that would make a poor casting surface