how do i make a mold or cast of a pre-existing plaster cast with out ruining it?

Question

I already have a cast of a face made of something that looks like plaster of paris, I would like to make a replica of it, but dont know where to start.

Answer 1

Most easily you make a sectional rubber mold that can be removed by flexing it. The sectional rubber mold is backed by plaster to enforce its shape. The whole is reassembled and new plaster poured inside. It is standard sculptural process which can be found in many books or you can look here
http://users.ticnet.com/mikefirth/castgobl.htm#HDFTGOB
to see it being done on a small scale. (look up and down on page)