Dating old tintypes
The process was first described by Adolphe-Alexandre Martin in France in 1853.
In 1856 it was patented by Hamilton Smith in the United States and by William Kloen in the United Kingdom.
Tintypes were sturdy and did not require mounting in a protective hard case like ambrotypes and daguerreotypes.
There are two historic tintype processes: wet and dry.
Such collodion glass positives had been invented by Frederick Scott Archer in 1851 and the name Ambrotype was introduced in the United States by James Ambrose Cutting in 1854 when he patented a variation of Archer's original process.
The tintype was essentially a variant of the ambrotype, replacing the latter's glass plate with a thin sheet of japanned iron (hence ferro).
They were often later transferred into the precut openings provided in book-like photograph albums.
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.In both processes, a very underexposed negative image was produced in the emulsion.The image as a whole therefore appeared to be a dull-toned positive.This ability to employ underexposed images allowed shorter exposure times to be used, a great advantage in portraiture.
Search for dating old tintypes:
Ambrotypes often exhibit some flaking of their black back coating, cracking or detachment of the image-bearing emulsion layer, or other deterioration, but the image layer on a tintype has proven to be typically very durable.