Tintype, also melainotype and ferrotype, is a photograph made by creating a direct positive on a sheet of iron metal that is blackened by painting, lacquering or enamelling and is used as a support for a collodion photographic emulsion.
Photographers usually worked outside at fairs, carnivals etc. and as the support of the tintype (there is no actual tin used) is resilient and does not need drying, photographs can be produced only a few minutes after the picture is taken.
An ambrotype uses the same process and methods on a sheet of glass that is mounted in a case with a black backing so the underexposed negative image appears as a positive. Tintypes did not need mounting in a case and were not as delicate as photographs that used glass for the support.
Technical details 
The process is very similar to wet plate photography, where silver halide crystals are suspended in a collodion emulsion that is chemically reduced to crystals of metallic silver that vary in density in accordance with variations in the intensity and duration of light impinging on the emulsion.
In a tintype, a very underexposed negative image is produced on a thin iron plate, lacquered or otherwise darkened, and coated with a collodion photographic emulsion. Since in a negative image the darker portions of the subject appear lighter, or in this case more transparent, the dark background gives the resulting image the appearance of a positive. The ability to employ underexposed images allows effective film speed to be increased, permitting shorter exposure time, a great advantage in portraiture.
One unique piece of equipment was a twelve-lens camera that could take a dozen 3/4" x 1" "gem-sized" portraits in one exposure. Portrait sizes ranged from gem-sized to 11" x 14". From about 1865 to 1910 the most popular size, called "Bon-ton", ranged from 2-3/8" x 3-1/2" to 4" x 5-3/4".
The process was first described by Adolphe-Alexandre Martin in France in 1853, patented in 1856 both in the United States by Hamilton Smith and William Kloen in the United Kingdom. It was first called melainotype, then ferrotype by a rival manufacturer of the iron plates used; finally tintype.
Ambrotype as a precursor 
The ambrotype was the first use of the wet-plate collodion process as a positive image. 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 on Archer's original process.
Success of the tintype 
The tintype process became very popular in United States particularly during the Civil War. They continued to enjoy significant use throughout the 19th century for inexpensive portraits, particularly by street photographers.
The tintype can be seen as a modification of the earlier ambrotype, replacing the glass plate with a thin sheet of japanned iron (hence ferro). The new materials reduced costs considerably; and the collodion image has proven to be very durable. Like that of the ambrotype, the tintype's image can be thought of as a negative; but, because of the black background, it appears as a positive. Since the tintype is a camera-original positive, most tintype images appear reversed (left to right) from reality. Some cameras were fitted with mirrors or a 45-degree prism to laterally reverse the image.
Tintypes are simple and fast to prepare, compared to other early photographic techniques. A photographer could prepare, expose, develop, and varnish a tintype plate in a few minutes, quickly having it ready for a customer. Earlier tintypes were sometimes placed in cases, as were daguerreotypes and ambrotypes; but uncased images in paper sleeves and for albums were popular from the beginning.
Ferrotyping is a finishing treatment applied to glossy photographic paper to bring out its reflective properties. Newly developed, still-wet photographic prints and enlargements that have been made on glossy paper are squeegeed onto a polished metal plate called a ferrotyping plate. When these are later peeled off the plate, they retain a highly reflective gloss.
See also 
- Rinhart, Floyd; Rinhart, Marion (1990). The American Tintype (in English). Ohio State University Press.
- "What Do You Know About Tintypes?", Ohio Historical Society Collections Blog, 2011-08-05.
- Peres, Michael R. The Focal Encyclopedia of Photography, p. 32.
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