clay casting how-to
 
step 1
use clay to form a model of a
cup as desired. the model
has to be a little bigger since
the clay will shrink in the mold
after casting.
step 2
surround the model with a
water resistant tube and seal
the bottom against leakage.
step 3
pour liquid plaster into the
cavity between the model
and the tube...
step 4
...until the model is entirely
enclosed by the plaster.
wait for the plaster to solidify.
step 5
once the plaster has set,
remove the tube and lift the
mold off the plate. then remove
the clay from the cavity.
now you have a mold that can
be used to make the same cup
many times.

before casting the first cup
wait for the mold to dry
entirely. otherwise the plaster
is not capable of absorbing
enough water from the liquid
clay.
step 6
pour liquid clay into the cavity.
as the plaster absorbs water
it may be necessary to add
more clay.
step 7
depending on the degree of
dryness of the mold, the water
content of the liquid clay and
the desired wall thickness
of the cup the liquid clay is
kept in the mold between about
15 to 30 minutes. then the
remaining liquid clay is
removed.
in order to obtain an even rim
it is best to cut off the waste
clay at the top while still in the
mold.
step 8
when the clay has shrunken a
little and is dry enough to be
touched, without leaving
pressure marks, remove the
piece from the mold.
the clay should still be soft
enough so in case the cup has
become oval it can be adjusted
slightly.
step 9
the cup has to be dried
thoroughly before firing.

the edges of the cup can be
smoothed with sand paper
once it is has dried.