This Instructable written by MAKE’s Tim Anderson, documenting the process of Chinese lifetime gourd craftsman Zhang Cairi, focuses on growing gourds into molds shaped to produce portrait busts. But it could be generalized to grow pretty much any hollow form. A speaker horn? A flashlight body? An enclosure for an Arduino or other PCB? A robot chassis?
The master is sculpted in clay, then latex is painted on to produce a slip-off negative, which is filled with plastic resin to produce a duplicate positive. Finally, a two-part negative mold is cast around the resin positive, separated, and secured around the immature gourd with string or wire. The mold needs to be suspended in such a way that the vine doesn’t have to bear its weight.