The history of photography has been one of constant trial, error, and experimentation.  Numerous photographic processes were developed over the past 200 years.  Most were eventually abandoned due to newer processes producing better images in a simpler fashion.
All nondigital processes rely on the ability of light to alter a chemical in such a fashion that a permanent image is created on paper, celluloid, glass or other surface.  Most techniques produce an image composed of microscopic metal particles imbedded in paper fibers or in a binder such as gelatin on the paper surface.
The most commonly used photographic metal is silver which is held in place on paper in an emulsion of gelatin. These are referred to as Silver prints, or just silver prints, and are the very common everyday photographs produced throughout the 20th century.
There were several other processes which used silver to create an image: Albumen prints, Daguerreotype, salted paper, Kallitype, Aristotype and others. Other metals used to produce images were iron, gold, platinum, and palladium.  Even uranium was incorporated into images to adjust the color. Gelatin itself can be made sensitive to light and produce an image of pigment in the Carbro and Carbon prosesses.

It has always been my feeling that historical processes still have value in producing contemporary imagery, just as stone has been used by sculptors for millennia to produce work ranging from primitive mythical figures to the abstract forms of Brancusi and Henry Moore.