This ability to employ underexposed images allowed shorter exposure times to be used, a great advantage in portraiture.
Chemical treatment then reduced the crystals to microscopic particles of metallic silver in proportion to the intensity and duration of their exposure to light, resulting in a visible image.
The later and more convenient dry process was similar but used a gelatin emulsion which could be applied to the plate long before use and exposed in the camera dry.
The glass was either of a dark color or provided with a black backing so that, as with a tintype, the underexposed negative image in the emulsion appeared as a positive.
Tintypes were sturdy and did not require mounting in a protective hard case like ambrotypes and daguerreotypes.
One or more hardy, lightweight, thin tintypes could be carried conveniently in a jacket pocket.
They became very popular in the United States during the American Civil War.Although prints on paper soon displaced them as the most common type of photograph, the tintype process continued to enjoy considerable use throughout the 19th century and beyond, especially for casual portraiture by novelty and street photographers.John Coffer, a featured photographer in the New York Times, travels by horse-drawn wagon creating tintypes.Compared to their most important predecessor, the daguerreotype, tintypes were not only very inexpensive, they were also relatively easy and quick to make.A photographer could prepare, expose, develop and varnish a tintype plate and have it ready for the customer in a few minutes.It was perhaps the most acutely hazardous of all the several highly toxic chemicals originally used in this and many other early photographic processes.