Nik Douglas (1944-2012) and Penny Slinger are the authors of "Sexual Secrets, Erotic Sentiment: In the Paintings of China and Japan" and "The Secret Dakini Oracle", and Douglas is the author of "Spiritual Sex "and "The Path of the Mystic Lover". Douglas studied Eastern art, philosophy, and sexual traditions while living for eight years in the Himalayas. He was one of the world's leading authenticators of Oriental art.