The secret of the transformation scenes for the 1931 version of Dr. Jekyll and Mr. Hyde was actually not revealed for decades. Eventually, director Rouben Mamoulian himself revealed the technique in a volume of interviews with Hollywood directors published under the title The Celluloid Muse. In short, make-up was applied in contrasting colors. A series of colored filters that matched the make-up was then used which enabled the make-up to be gradually exposed or made invisible and because the change in color was not visible on the black-and-white film, it created seamless sequences. One that, to this day, are iconic along with Wally Westmore's make-up for Hyde ( Simian and hairy with large canine teeth) which greatly influenced the popular image of Hyde in media and comic books. Stay tuned!