How long to leave the slip in, how to drain the mold, and when the cast is ready to come out.
Drain casting works because dry plaster draws the water out of the slip: a wall of firm clay builds against the plaster while the middle stays liquid. You pour the liquid back out, and the wall that stays is your piece. The pour sheet of your piece has these steps with its own amounts.
Stir the slip slowly from the bottom so no air goes in, then pour it through a 60 to 80 mesh sieve into the jug. If the mold is in pieces, brush the dust off their faces, seat them on their natches and band the mold tight: slip pushes hard on the seams.
Pour in one steady stream until the spare is full. Do not stop halfway, or a line shows on the cast.
Top up as the level drops. About 15 minutes gives a wall near 3 mm, and a damp mold takes longer: 10 to 20 minutes in all. Check the thickness at the spare before you drain. Leave the slip in longer for a thicker wall, drain sooner for a thinner one.
Pour the slip back into the bucket slowly. Then leave the mold upside down on two sticks over the bucket to drip, for 15 to 20 minutes. Do not shake it.
Wait until the shine has gone and the clay has pulled away from the plaster: 1 to 4 hours after filling. Cut the spare off level with the rim. Take the bands off and lift each piece straight away from the cast. A mold of one piece you turn over onto your hand, and the cast drops out.
Let the cast stiffen for a few hours. At leather hard, pare the seam lines with a fettling knife and smooth them with a damp sponge.
Every cast repeats these steps. Let the mold dry between casts until it no longer feels cold and clammy. A new mold often gives one or two poor casts first.
Tiles and plates are cast solid: nothing pours back out, and their pour sheets have their own steps. If a cast sticks, tears or comes out too thin, see When a cast goes wrong.