B&W film stock sensitive to blue and green, insensitive to red — produces exaggerated skin tones, dark lipstick. Mostly historical; rarely used today.
Orthochromatic Film
Anyone who loads orthochromatic material into the camera is working with a black-and-white raw film that sees blue and green but is completely blind to red. This sounds like historical baggage — and it is. But anyone who wants to understand why old silent films look so bizarre has to deal with this stuff. Sensitivity not only determines how bright or dark an image becomes, but also how colors are converted into grayscale. And that's exactly the crux: skin appears overexposed, almost white. Red lips or blush turn black as coal. Blue-eyed actors get extremely bright eyes, redheads the darkest hair. This was a real catastrophe for characterization on set.
Why was this stuff used at all? Because Ortho was cheap and lasted a long time. Mainly prevalent between the 1910s and late 1920s — parallel to the introduction of Panchromatic, which saw red and delivered realistic skin tones. Those who had to shoot cost-effectively stuck with Ortho. This led to bizarre twists: makeup artists applied thick layers to differentiate faces. Contouring before Instagram — only with theatrical makeup and the hope that the film's red blindness would at least have an effect.
Today? Practically dead. Eastmancolor and digital sensors have replaced it. But artists still use it occasionally — experimental film, archaeology of the image. The exaggerated contrasts, the false skin tones — these are no longer mistakes, but aesthetics. Anyone who wants to use it seriously (and this is damn rare) has to work with extreme lighting and think about color filters on set completely differently than with modern material. Panchromatic film has long since replaced orthochromatic — more light sensitivity, more realistic color reproduction. That was the next step in film technology, and it was a big one.
Still relevant in archival work: anyone digitizing old negatives needs to know what material they were shot on. The conversion requires different approaches through color separations. Camera enthusiasts occasionally experiment with it, but it's as specialized as hand-crank cameras. Irrelevant for current productions.