Gelatin silver printing has been the primary black-and-white process since its development in the late 1880s and consists of three layers—paper, baryta, and gelatin—on which an image is produced. The paper essentially serves as a base, with the baryta layer (a surface preparation of barium sulfate) sitting on top to separate the image-containing gelatin layer from the paper support. The gelatin layer is made up of an emulsion that consists of light-sensitive silver compounds that form the image following exposure of the negative and development in a chemical bath. Another distinguishing feature is the smooth, even image surface. Photographers often use additional chemicals on gelatin silver prints in order to alter the range of tone and make the print more permanent.
Irving Penn. Zebra, Prague, 1986. Gift of Irving Penn 1996.180.