Molds are easy, use latex to cover the whole thing and let it dry, then put your plaster over that to keep the mold "workable" then you pull the whole thing out and the latex is very pliable, and you peel it off of the existing piece, then pop it back into place, put back into the plaster cast, and pour your mix, let it harden, pull it out and peel the latex off again, viola, cast and mold making 101...