Collodion Process - Origin of The Process

Origin of The Process

In 1851, Frederick Scott Archer introduced a wet plate process, sometimes referred to as the collodion process after the carrier material used. The process is simple: a bromide, iodide, or chloride is dissolved in collodion (a solution of pyroxylin in alcohol and ether). This mixture is poured on a cleaned glass plate, which is allowed to sit until the coating gels but is still moist. The plate is then placed in a silver nitrate solution, which converts the iodide, bromide, or chloride to silver iodide, bromide or chloride. Once the reaction is complete, the plate is removed from the silver nitrate solution and exposed in a camera while still wet. The plate loses sensitivity as it dries, requiring it to be coated and sensitized immediately before use. It must also be developed while still moist, using a solution of iron sulfate, acetic acid and alcohol in water.

The sensitivity of silver halides to light is the underlying principle behind most types of 19th century photographic processes (Daguerreotypes, Ambrotypes, Calotypes that use paper negatives, and wet and dry plates) as well as modern 20th century photographic film processes.