Pinholes, a cast that sticks or tears, a wall too thin or too thick, plaster that grabs the case or leaks: the likely cause and what to do.
Each piece's pour sheet ends with the same kind of table for its own mold. These are the common ones.
The likely cause is air in the slip, or a mold that is bone dry. Stir slowly, sieve, and pour in one steady stream. Wipe a bone-dry mold with a damp sponge 5 to 10 minutes before you pour.
It was released too early, the mold is wet, or a new mold still has soap film on it. Wait until the clay pulls away from the plaster. Dry the mold longer between casts. A new mold often gives one or two poor casts first.
That is the time the slip stayed in the mold. For a thicker wall leave the slip in longer; for a thinner one drain sooner. A mold that is still damp casts slower.
Too little soap, or the case was opened while the plaster was still warm. Let it go cold, then flex and tap the case walls. Next time give it three full coats of soap.
The cut faces were not sealed, or a clamp is not fully down. Press soft clay over the leak at once. Next time put jelly on both faces and seat both clamps.
One face dried faster than the other. Dry it slowly on a flat board, out of drafts, and turn it over once it can be handled.
The cup ran dry while the plaster drank, or air was caught at the top. Keep the cup topped up for the first half hour, and pour slowly so the air leaves through the vent.
If none of this fits, ask a person. Say which piece it is and add a photo if you can: it shows what words cannot.