Slipcasting is a molding process for ceramics that can be used to produce hollow forms having a relatively thin shell. It allows access to many of the same types of shapes as rotomolding, in plastics, but without the requirement of an elaborate, ungainly gimbal apparatus to spin the mold on two axes simultaneously.
Slipcasting is an ancient, elegant, ingenious technique, consisting of six basic steps:
- A negative mold of the form is prepared in plaster.
- The negative volume is completely filled with liquid clay “slip” through an opening in the mold, which can be small.
- The slip is allowed to sit in the mold for a short period, during which the plaster absorbs water from the clay volume through its outer surface, causing it to thicken and solidify there, first. The thickness of this solid layer can be controlled by how long the slip is allowed to sit.
- The liquid slip remaining at the center of the form is poured off. The layer of dehydrated, solidified clay lining the surface of the mold remains in place and is allowed to dry for a long period.
- After the long drying period, during which the clay layer shrinks slightly away from the plaster, the mold is opened, separated from the form, and dried apart. The molds can be reused a few times.
- The hollow slip-cast clay form can now be glazed, fired, and/or otherwise prepared as usual.
There is some good slipcasting info on the web if you dig a bit, but the best and most beginner-friendly phototutorial I’ve seen, so far, comes to us from Wired Design writer Allison Arieff, husband Bryan Burkhart, and daughter Emilia, who published the linked tutorial, below, back in April. A more advanced, detailed, academic introduction to slipcasting can also be found here.