Make the Core Boba straws (big for legs) and regular straws (arms and neck). Wrap straws in floral tape if using paper clay. They will stick to it better that way
You can make the core out of tiny carboard boxes, styrafoam, model magic
Make the inside of the doll so you can sculpt around it
Form the clay on top of your core to make the skeleton. Make sure you about 1/4th” of thickness of the skeleton.
Clay Mold Materials: Super Sculpy, or Super Sculpy Firm, Premier stone clay, Creative Paperclay
(If you use a Paperclay you must seal it with krylon or something before casting)
Sculpt the doll parts. Make the body as one and cut out the separate parts. Make the arms and legs as one and cut them too using marbles as joints.
Make a Cast Materials: Plaster does not work. Silicon molds such as Oomoo for beginners or Mold Max 30 for finals works for Batchix (BJD maker)
Casting Materials 2: Legos, vaseline
Cast the clay doll using legos and the pourable mold. Put straws in the neck, and arms.
You will get about 10 sculpts or 1 year out of the mold. Each time you make a mold your cast shrinks a little. The better quality the silicone the less it shrinks. It takes Batchix 1 gallon of silicone to make the junk mold for a 42cm doll which is about $130.
Resin Materials: Polyerthane Resin such as Polytek resin, Alumalite (make sure you use UV stabilizer)
"Make your original in clay then cast it in resin. That is your junk cast. Refine that cast more and it becomes the “master cast.” That is what you send to the molding company (only use a resin cast to send to a company since it is stronger . Make your own mold of the master before you send it off just in case it gets dead. The mold they send back to you (professionally cast in resin) is called the sample." –Batchix
Use magnets to keep the head cap on
Professional Casting Service Companies: Bobobie, MU Doll (100 order min)