The light-sensitive coating given to photographic materials. It consists of crystals (usually called grains) of silver halides, suspended in gelatin which is coated on to a base of glass or film. The emulsion's sensitivity to light depends on the size of the grains, the most sensitive (fastest) emulsions having the largest grains. The basic emulsion is sensitive only to ultraviolet and blue light, but by adding organic dyes the grains can be made sensitive to other colours. On exposure to light, small specks of metallic silver are created on the surfaces of the grains. These then trigger the conversion of the whole grain to silver when the emulsion is placed in developer.
Subjects: Astronomy and Astrophysics — Chemistry.