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Collodion is a solution of nitrocellulose in ether or acetone, sometimes with the addition of alcohols. Its generic name is pyroxylin solution. It is toxic and highly flammable. As the solvent evaporates, it dries to a celluloid-like film. It was discovered about 1846 by the french chemist and writer Louis Ménard.

• Celloidin is a pure type of pyroxylin used to embed specimens which will be examined under a microscope. [1]

In 1850, Frederick Scott Archer discovered that collodion could be used as an alternative to albumen on glass plates. This also reduced the exposure time when the plate was used damp. This became know as the wet plate method or wet collodion method. Collodion was also grainless and colorless, and allowed for one of the first high quality duplication processes.

In order for photographers to adequately prepare the glass plates, each plate would have to have collodion applied to it in order to keep the plate wet. This meant that the photographer would have to carry the chemicals with him wherever he went.

See this page for more information collodion process

Richard Norris, a doctor of medicine and professor of physiology at Queen's College, Birmingham, is generally credited with the first development of dry collodion plate in the 1860's, in 1894 he took out a new patent for dry plate used in photography.

One example, Compound W Wart Remover, still exists, consisting of acetic acid and salicylic acid in an acetone collodion base. Pyroxlin solution is also used presently in MedTech's NewSkin liquid bandage product.

• Collodion was widely used to glue electrodes to the head for electroencephalography until the 1990s. It has been replaced by water-based gels in most uses to avoid the contact with acetone, which is not only contained in the glue but needed in quantity for electrode removal.

• Pyroxylin with added pigments is used as a nitrocellulose lacquer.

• It was also added to nitroglycerine to stabilise it as blasting gelatine.
• Collodion is also used in theatrical makeup for various effects, such as simulating old-age wrinkles or scars.
• Collodion also finds use in the cleaning of optics such as telescope mirrors. The collodion is applied to the surface of the optic, usually in two or more layers. Sometimes a piece of thin cloth is applied between the layers, to hold the collodion together for easy removal. After the collodion dries and forms a solid sheet covering the optic, it is carefully peeled away taking contamination with it.

• Contemporary Wetplate Collodion Photography
• Contemporary 19th Century Wetplate Collodion Photography
• Collodion: Material Safety Data Sheet
• Compound W data sheet
• Modern images of the ambrotype process