I've only ever heard of lost-wax casting being used for casting metal.. And even then, the masters are usually made in whatever the artist feels like, not necessarily wax.
With lost-wax, the master is used to make a mould (probably rubber of some sort), which is then filled with wax. The wax cast is cleaned up (remove mould marks, etc) and has sprues added, and then is used to create a second mould made out of investment, which is the one you pour the metal in.