This is an interesting article from Todays Machining World magazine.
http://www.todaysmachiningworld.com/how-it-works-where’s-the-steel/
How ironic… i was reading that article and saw some quotes from a guy at GMSI in Tempe AZ… one of those guys… the GM came to my shop in Mesa a couple years back. He wanted to do some machining of graphite molds for us. Back then i thought in my head… crap i can’t afford graphite material cost… LOL… apparently it is inexpensive material. I saw a mold he made for a friend and it was very nice. So if you need a small mold graphite works well from what i hear for laying up composites.