Back in the beginning of photography, film and plates were orthochromatic. Orthochromatic means the material isn't sensitive to red light. That makes processing easier, since then it's possible to navigate a darkroom, load film, and even develop "by inspection". But since any subject with the color red in it became darker with Ortho film, certain scenes became problematic. Blue skies were rendered white, skin color with more red pigment went dark, freckles and zits were emphasized. In the early part of the 20th Century, panchromatic films became the norm. Ortho film was still the norm for many technical uses of photography. For example copywork, typesetting, etc. But with panchromatic film, tonalities of the world around us were more accurately mapped to their associated gray tones. Today, when film photography itself is already a rarity, I've opted to play with the unusual characteristics of film including the color sensitivity. What happens to a red rose on a