An ambrotype is a weak negative image on glass rendered positive by the addition of a dark background. Frederick Scott Archer, an English sculptor, discovered that light-sensitive silver salts could be mixed with collodion, a sticky liquid that rapidly hardens and which had seen use as a field bandage for the British military.
430 mm x 360 mm
Art Gallery of New South Wales
This mixture could then be applied to a glass plate and exposed in a camera while still wet; hence the term "wet plate process." In 1854, James Cutting of Boston took out a patent on this process, and Marcus Root coined the name "ambrotype" for it, from the Greek ambrotos (immortal). The process was cheaper and easier than the daguerreotype and contributed to the demise of that earlier process. Like the daguerreotype, an ambrotype was also produced as a unique object, although in principle, a print could be made from the negative on the glass. For an illustration of how a dark background makes the negative ambrotype plate look positive.
Whole plate 16.5cm x 21.5cm
Half plate 11.5cm x 14cm
Quarter plate 8.2cm x 10.8cm
One-sixth plate 6.8cm x 8.2cm
One-ninth plate 5cm x 6.3cm
Using the same case as a daguerreotype, the ambrotype was sealed inside a wooden case or a frame with a bright brass mount and under glass. The case was usually provided with a hinged lid and covered with leather or similar and some American cases were moulded using shellac with wood-fibre and gum and known as a Union case. The cases should not be taken apart or interfered with in any way.
There is little to date them, as often no studio is named, so the best way is to see what the people were wearing (not easy). As a rough guide few will be as early as 1854, but large numbers were produced around 1858 before carte-de-visite were produced (1859/1860) and not so many up to 1866 (no real cut off date). So the bulk of them would be c.1858 plus or minus a few years.
The tintype is actually an image produced on a very thin piece of iron, not tin. The process is quite similar to the ambrotype: the light-sensitive collodion mixture is applied to the iron plate and exposed in the camera while still wet. Because the plate has previously been given a black finish, the negative produced by the camera actually results in a positive image. Hamilton Smith, a chemistry professor at Kenyon College in Ohio, discovered this process in 1854. His student Peter Neff financed the development of the process and patented it in 1856.
Tintypes were even cheaper than ambrotypes. They were also durable and could be sent through the mail. Hundreds of thousands of soldiers during the Civil War had tintypes made by studio or itinerant photographers to leave as mementos with loved ones and friends or to send home by mail from the front. Tintypes rapidly supplanted both daguerreotypes and ambrotypes because they were cheaper, easier to produce, and readily transportable. Other names for the tintype include "melainotype" and "ferrotype." Tintypes are also unique items like the daguerreotype, although some studios employed multiple lens cameras to produce multiple images from a single portrait sitting.