I picked up a costume piece last year at a clearance sale (best way to halloween shop) thinking I would cut it up and just use the skull part, but its really to flimsey so I decided to use it as a mold
Step 1: the materials
I use this mix of materials for a lot of things, Its very close to paper mache' but it dries hard like plastic, its also very moldable and sandable if you soak the tissue in the glue/paint/water mix. Ive never tried a mold with this many different planes so I was really hoping it would work, in hindsight I probably should have used a release of some king (like cooking spray) or maybe just allowed more time for it to dry...
you'll need a mold of some kind
white school glue
acrylic craft or artist paint
toilet paper or face tissue or papertowel (paper towel doesn't mold as easily to some shapes but it adds strenght in areas that need it)