Another thing is the production of silver grains in the photographic emulsion. The change in color depends upon the chemical make-up of the photographic emulsion being toned. Originally, film was a strip of cellulose nitrate coated with black-and-white photographic emulsion. Photograms may be made outdoors providing the photographic emulsion is sufficiently slow to permit it. A straightforward example of this is photographic emulsion on a transparent substrate. Photographic emulsion is a light-sensitive colloid used in film-based photography. Such a photographic emulsion consists of silver halide colloidal particles dispersed in a gelatin matrix. In 1874, Abney developed a dry photographic emulsion, which replaced "wet" emulsions. A visiting scholar, Gilberto Bernardini, created the first photographic emulsion of a meson.