Head Casting Help

[TCH Props]

Hey everyone, I'm working on making a cast of my full head and bust, and I know what I'm going to do for the mold part, but I'm not sure what I should use to cast it. I initially thought of using plaster of paris, but I'm using it to make clay mask molds to cast out of silicone and patterns for helmets and such (as per the Evil Ted instructions on YouTube) and don't want it to be something so easily cut when cutting out patterns.

Any ideas what medium I should use to cast my head mold that can stand up to an exacto blade and still capture a high level of detail for mask molding as well?

 

[Duncanator]

If you want to stick with a a water based casting material: instead of plaster of paris, I would suggest using hydrocal or ultracal. They are like plaster but much stronger and harder.
Check out Artstuf.com if you can't find it locally.