About two days after the molding is finished, the clay starts to shrink and separate from the mold.

It is time now to push in on the convergent side about 1/4"

and to cut with a knife or similar tool to create the base of the nozzle on the divergence side.

Finally the whole nozzle is removed from the mold and left to dry for five more days or as needed to completely dry, otherwise it can crack or explode in the oven when firing.

The ideal way to cook (fire) the clay is to do it on a specialized ceramics oven or kiln. I found a local ceramicist that will fire them for me at a low cost. I really don't know if a house oven would do the job but it is worth to give a try.