Panchromatic Emulsion
A black and white emulsion sensitised to all visible wavelengths, rendering colours as plausible grey tones.
Measured in
nm
In depth
Early emulsions were blind to red, which made skies white and lips black. Panchromatic sensitisation, standard from the 1920s, corrected this and gave monochrome photography its modern tonal vocabulary. The cost is that it cannot be handled under any safelight, so panchromatic film must be loaded and developed in total darkness.
Examples in practice
A red apple on a green cloth renders as two distinguishable greys on panchromatic film, where an earlier emulsion showed both as black.