Do NOT mix the two together! Plaster moldmaking & slip casting are not
the same thing.
Slip is poured into plaster molds until a 3/8" or so thick wall is
formed inside the mold. The excess slip is the poured off and the mold
left to dry until piece begins to shrink away from mold (thereby
releasing). Do not use any type of mold release- it will ruin the mold
by clogging the pores in the plaster. This cast time will vary
depending on a number of factors: the size of the mold you are casting,
how dry/wet the mold is(how many times the mold has recently been cast),
how humid & hot or cold the day is, the specific gravity of the slip
etc., etc.. Do not cast the piece solid unless it is a very small or
flat back (one piece) mold. It most likely will crack or explode in the
kiln. The idea here is to create an object of uniform thickness.
De-mold carefully, this may take practice depending on the complexity of
the mold. Be prepared to lose a few pieces at first -be
patient!!REmoving a peice too early-you will tear it and it may stick to
the mold. Remove it too late and it may be cracked. REpair any cracks or
defects with wet slip and let dry. Remove seams, sand ,wet sponge etc.
Take all the usual precautions with dust etc., etc....
Slip casting is a great thing to teach ceramic students as it exposes
them to the prospect of production ceramics ( a viable way to make a
living in art!).
Moldmaking is another process altogether-also worthwhile. TO extensive
to describe here-at least I don't have the time-but I recommend you get
a couple books from the library and look them over-there are many good
This is obviously the short course but for what its worth..
I have made a living at slip casting and mold making for 20 years and
have made all the mistakes (and more) mentioned above.
I teach art on a volunteer basis to my children's elementary school 2X a
The Porcelain Rose
Long Beach CA