Karl Struss: B&W Special Effects with Filtration

From American Cinematographer, Two-Faced Treachery by George Turner (March 1999)

"The first time Jekyll changed, we used a technique I had devised years before to show the healing of the lepers in Ben-Hur [1926]. Everybody was using orthochromatic film then, which reproduced reds and yellows as black, and gave blue-eyed actors 'fish-eyes.' I had begun using panchromatic film, which is sensitive to all colors. The leprosy spots were red makeup, which registered when shot through a green filter, but when we gradually moved a red filter over the lens, the makeup disappeared. The Hyde makeup was also in red and didn't show at all when the red filter was on the lens, but when the filter was moved down very slowly to the green, Mr. Hyde appeared."

- Karl Struss, ASC