Terra Cotta? Epoxy Sculpt?

Hello all!

I'm new here. I'm taking ceramics at the university to help with my sculpting and building. I saw Danger Russ's iron man helmet and it gave me inspiration to make one as well. I wanted to know if is it possible to make the mold out of white clay or terra cotta? I notice that many people use epoxy sculpt but I've never sculpted with that. I'm assuming that there is no difference because its a sculpt and a negative will be made of it with silicone.

Also a quick question on slush casting, smooth cast roto when poured into the mother mold and swished around, is my product is a smooth hollow cast of my negative (I'm sorry I am not using these terms correctly)? Is the strength of smooth cast roto the same as resin? Why do people use smooth cast roto instead of resin?

Thanks for your time to read questions of a newb!

roto is just one of smoothon's flavors. i use it because it stays somewhat flexible, so it's got a great impact resistance.