The Collodion Process was introduced in 1851 and marked a watershed in photography.
Up to that point the two processes in use were the daguerreotype and the calotype. Daguerreotypes were better than calotypes in terms of detail and quality, but could not be reproduced; calotypes were reproducible, but suffered from the fact that any print would also show the imperfections of the paper.
The search began, then, for a process which would combine the best of both processes - the ability to reproduce fine detail and the capacity to make multiple prints. The ideal would have been to coat light sensitive material on to glass, but the chemicals would not adhere without a suitable binder which obviously had to be clear. At first, Albumen (the white of an egg) was used. Then in 1851 Frederick Scott Archer came across collodion.
Collodion was a viscous liquid - guncotton dissolved in ether and alcohol - which had only been invented in 1846, but which quickly found a use during the Crimean war; when it dried it formed a very thin clear film, which was ideal for dressing and protecting wounds. (One can still obtain this today, for painting over a cut). Collodion was just the answer as far as photography was concerned, for it would provide the binding which was so badly needed. Lewis Carroll, himself a photographer who used collodion, described the process in a poem he called "Hiawatha's Photography."
"First a piece of glass he coated
With Collodion, and plunged it
In a bath of Lunar Caustic
Carefully dissolved in water;
There he left it certain minutes.
Secondly my Hiawatha
Made with cunning hand a mixture
Of the acid Pyro-gallic,
And the Glacial Acetic,
And of alcohol and water:
This developed all the picture.
Finally he fixed each picture
With a saturate solution
Of a certain salt of Soda...."
" This "soda" was, of course, hypo. Sometimes potassium cyanide was used, the advantage of this being that the solutions could be washed out by rinsing under a tap for a minute or so, whereas hypo would need much more washing time.
The collodion process had several advantages. Being more sensitive to light than the calotype process, it reduced the exposure times drastically - to as little as two or three seconds. This opened up a new dimension for photographers, who up till then had generally to portray very still scenes or people. Because a glass base was used, the images were sharper than with a calotype. And because the process was never patented, photography became far more widely used. the price of a paper print was about a tenth of that of a daguerreotype.
There was however one main disadvantage: the process was by no means an easy one. First the collodion had to be spread carefully over the entire plate. The plate then had to be sensitised, exposed and developed whilst the plate was still wet; the sensitivity dropped once the collodion had dried. It is often known as the wet plate collodion process for this reason.