Ordinary emulsion refers to a photographic emulsion that is naturally sensitive only to ultraviolet and blue light. This type of emulsion was commonly used in early black-and-white photography before the development of panchromatic emulsions, which are sensitive to the full visible spectrum.
Because ordinary emulsions respond primarily to shorter wavelengths, they render red and yellow tones much darker in black-and-white images. Understanding the characteristics of ordinary emulsion is important for photographers working with historical processes or seeking specific tonal effects in ultraviolet or blue-sensitive photography.