The basic techniques of diamond cutting haven't changed since the 16th Century. From NATURE's "Diamonds" airing Sunday, September 30th at 8 p.m. (ET) on PBS (check local listings). The program examines the oldest, hardest natural substance in the world - diamonds -- from their beginnings in the core of the earth, through mining and acquisition, to the history of the most famous of these extraordinary gems. Actress Stockard Channing narrates the program. For more information, visit http:/www.pbs.org/nature