Last year I made a Bird skull for a friend.
Step 1: Plywood Positive
I Laser cut the skull model out of aircraft plywood (.0625")
Using Illustrator I drew one side and then mirrored the other side making it symmetrical.
This was the third one I made.
Step 2: Bondo
Bondo, yeah this messed with the mold material but it's cool.
Step 3: Mold
I used Mold Max 30, looks like I rigged something cause I didn't have enough material.
Step 4: Pour Plastic
I use Smooth Cast 300.
Step 5: DeMold
After the plastic cures, put out the Skull.