The Wet-collodion method, often known as the collodion process, was devised in 1851 by Englishman Frederick Scott Archer. Because the collodion film became waterproof after drying, and the reagent solutions could not penetrate it, immediate development and fixing were required. The best way to do this was with heat, so an open pan was used instead of a closed tank. The hot plates used in photoengraving bake the image onto the glass plate without damaging the surrounding area.
Archer's invention was an important step toward the modern photography industry that we know today. He obtained very good results with the collodion process, but it had several limitations that prevented it from becoming the standard photographic technique it is now. Collodion is a difficult material to work with, and the process requires many time-consuming operations: coating the glass plate with a thin layer of gelatin; exposing it to light through a negative image; developing the exposed plate using strong acids or alkalies to remove any un-exposed areas of gelatin; and finally, fixing the image by washing it with alcohol or other solvents.
These steps had to be done under controlled conditions with great care not to damage the delicate photograph. The process was also very slow: only one inch by two inches per hour could be reproduced due to the labor-intensive nature of the task.
A photography procedure used in the mid-nineteenth century used a glass photographic plate covered with iodized collodion and quickly immersed in a silver nitrate solution before use. Also known as the collodion process or the wet collodion technique.
This was the first practical photographic process and it is considered the birth of modern photography. The term "wet plate" refers to the fact that the emulsion side of the glass plate is coated with a liquid (usually water based) before exposure. This is in contrast to modern photos which are taken on paper using dry chemicals.
Wet plates required special treatment before use and then had to be processed immediately after taking the picture. The processing consisted of washing, fixing, and drying the plate before covering it with a protective layer called "matting".
The quality of the image produced by this process was very good for its time but it was also very labor intensive and expensive to run. Only large scale photographers could afford to use it. It remained the dominant form of photography for several more years after it was invented, until the advent of the daguerreotype in 1839 and the ambrotype in 1842.
In conclusion, the wet plate process is an old technology that remains interesting today because of its historical value and the challenges it presents to modern photographers.
Following the wet collodion method, dry plate photography was created. As a result, the method was significantly more convenient than the wet collodion process, in which glass plates had to be manually coated with a wet, light-sensitive emulsion right before exposure and then developed nearly immediately thereafter.
The dry plate process used paper or plastic film instead of glass for its sensitive material. The paper or film was usually transparent, so it could be placed over the entire image once exposed. The negative sheet was processed just like a conventional silver gelatin print: It was dipped into a tank of processing chemicals to create an positive image that could be viewed later in a frame.
Dry plates were popular among photographers because they required less attention than glass negatives. If a paper or film negative got damaged during processing, it could be easily replaced without having to scrape away the previous image. However, if something went wrong with a dry plate, it was impossible to replace it. Once exposed, this type of negative could not be reused.
The first commercial dry plates were introduced by George Eastman in 1872. They were made from aluminum instead of glass, which allowed for thinner photographs. In 1891, Eastman also began manufacturing paper positives that could be used as masks for contact printing photos on cloth or other materials. These paper positives are still sold today under the Ektachrome brand name.