Best thing on the market right now is Body Double from Smooth on, but it is a tad epensive. The alternative is Alginate.
The short version is basically:
Make sure the model will be comfortable with having their entire head enclosed for 20-30 minutes or likely more. Make sure if they have any medical issues such as asthma that you are prepared should anything happen during the casting process (Ie an inhaler on hand). Make sure they are aware that they will only be breathing through their nose once covered. Get all of your materials ready in front of you before starting. It is usually helpful to have a partner help you.
- you put on a bald cap
- coat the face with vaseline (making sure it is smooth and can be a little heavier in any facial har)
- mix and coat the entire head with either the body double or alginate being careful to leave holes for breahting from the nose (some people use straws, but can be dangerous if they get jabbed or fall down). Make sure to work fast as these materials both set up pretty quickly. Another reason 2 sets of hands are helpful.
- while tacky add a little bit of cotton here and there to the alginate or body double
- coat the front of the head with plaster bandages 2-3 layers thick (again leaving breathing holes). make a neat edge at about the earline
- coat the edge of the front half liberally with vaseline
- coat the back half of the head with plaster bandages just like the front.
- once completely dry, carefully remove the plaster bandage shell, then the alginate or body double (you usually need to slit the back like a mask to get it off cleanly. Immediately place it into the shell and strap together.
- If working with alginate, you need to make your positive cast immediately as the alginate will shrink considerably. You only get typically one cast our of alginate. You can make several from body double, and the shrinkage is very minimal.
Hope this helps some. If you are nervous doing a full head right out the gate...try a face first. Whatever you do, do not use direct plaster of paris or ultracal/hydrocal on the face or any body part...it can create serious burns if you enclose a body part in it. My first attempt at a head cast in elementry school with a friend I got really lucky on. After watching the movie FX we decided we'd try it...and figured what they used was Plaster Of Paris. My face broke out pretty bad and it got pretty hot, but I think we got it off before any damage started....luckily. So yeah, be careful and never assume a material is unless you know somoene that has used it safely.
There are lots of great tutorials on youtube as well as books out there too.
Mike "Pogo" Hach