Top left: I have 3D printed a shell mold, and filled it will plaster to produce the model. Bottom left: I have smoothed the model on the wheel (using a metal rib and sandpaper). Then I stuck that down to the batt using a sticky clay slip. Then I soaped it. Bottom center: I glued the jigger head shell mold down using the same clay slip. Bottom right: I filled that with plaster. Top right: The mold is ready. Top center: Within an hour I filled that mold with a red stoneware slip to produce this piece (amazingly plaster is absorbent enough after setting to be able to cast). Notice how the plastic nursery pot fits: It's rim is too far down and the top diameter of the clay pot is a little too much.
Nursery Plant Pot