The Collodion-Albumen process is one of the early dry plate processes, invented by Joseph Sidebotham in 1861. The process lacked economical success because the plate was much less sensitive (about 1/4) and tended to have harder contrasts than wet plates. While the first was acknowledged by Sidebotham, the latter were disputed by him indicating the fact that the 1860 gold medal for the best landscape photography was made with a Collodion-Albumen plate (Recreative Science, 1861 P 43).

Why does it work?

There are several compounds unstable to light in this mixture, mainly silver iodine and

silver bromide Silver bromide (AgBr) is a soft, pale-yellow, water-insoluble salt well known (along with other silver halides) for its unusual sensitivity to light. This property has allowed silver halides to become the basis of modern photographic materials. A ...

. These decompose and leave

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

that is

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

by the developer (Pyrogallic Developing Solution). The excess of silver iodine and silver bromide are stabilized by the fixing bath. The

albumen Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms aro ...

mixture just encloses the

Collodion Collodion is a flammable, syrupy solution of nitrocellulose in ether and alcohol. There are two basic types: flexible and non-flexible. The flexible type is often used as a surgical dressing or to hold dressings in place. When painted on the skin, ...

in a dry environment.

Sources

*The Collodio-Albumen Process of Photography, Joseph Sidebotham (London : Recreative Science Vol II 1861) *History of Photography, Josef Maria Eder (Dover Publications, Mineola, NY, 1945) {{Photography-stub English inventions Photographic processes dating from the 19th century