Collodion, a thick and syrupy liquid, is made by dissolving nitrated cotton in a mixture of alcohol and ether. It was widely used by surgeons as a liquid bandage owing to its strength and adhesion.

In 1851, Archer used collodion to hold light-sensitive salts to his glass plates. Once the salts, such as potassium iodide, were in the mixture of collodion, the viscous liquid was poured onto the plate. Allowing the alcohol and ether to evaporate, a thin film containing the necessary iodides was left on the plate. Ready for sensitizing, the plate was placed in a bath of silver nitrate. This formed a light sensitive compound of silver iodide on the surface of the plate.

Once sensitized, the plate was exposed in the camera before the collodion began to set and dry. If the plate dried before development,it i would have had practically no sensitivity and would be therefore useless. For this reason alone, the process Archer invented became known as "Wet Plate" collodion process.

After exposure in the camera, the plate was quickly returned to the darkroom. Using an acidic solution of ferrous sulfate, the plate was developed, then rinsed and fixed in a mild solution of potassium cyanide, or hypo.

The wet plate photographers could now produce multiple images from a single negative or offer a collodion positive, such as the ambrotype or ferrotype, with speed and consistency. Not until the 1880's and the introduction of gelatin dry plates did wet plate photography command any less attention from the photographic world!

The ambrotype, made by the wet plate collodion process, is simply an underexposed glass plate negative. When placed against a dark background, it appears as a positive image.

The ambrotype plate is either backed with dark material or the plate itself is made of darkly colored glass, giving a dark background. The image is reversed, left to right.

It can be used only one time. Unlike albumin paper prints taken from dense glass negatives, the ambrotype requires additional sittings for duplicate copies.

Ambrotypes were often varnished to help protect the image surface and were always sold in cases or frames. Thus, the ambrotype is extremely durable and has withstood well the test of time.

The ferrotype, also called the melainotype or tintype, was America's first major contribution to the art of photography. It superceded the ambrotype by the end of the Civil War and went on to become 19th-Century America's favorite quick picture.

It was made the same way as the ambrotype, except that a thin piece of black enameled, or japanned, iron was used in place of glass. Like the ambrotype, the image is reversed.

Ferrotypes were made from thumbnail size to as large as 11" x 14". With the introduction of multi-lensed cameras with sliding backs in the early 1860's, the more typical small sizes were made in volume. These were usually mounted in card mounts of the then popular cart-de-viste size. Made on a metal plate and with a varnished surface, ferrotypes have proven very durable.