Until the 1970's, the Silver Gelatin black & white printing method was used almost exclusively by professional photographers. Color printing was used more commonly for commercial purposes. Although this process was the standard among the community, it's a complicated practice, thus it's virtually unused today. So what is a Silver Gelatin print and what does this process entail?
It was developed in the 1880s and consists of three layers. The main sources are of course Paper and Gelatin, but between that is a layer of baryta. Baryta is a barium sulfate combination. The Gelatin layer above it contains light-sensitive silver that develop the image upon processing in the darkroom. In the chemicals used, the silver reacts by getting darker in the blacks of the images, and more transparent in the whites. Additional chemicals are used to adjust the tone of the image and make it more stable. The process of developing is quite sensitive and requires attention to detail.