Frederick Scott Archer was the son of a butcher from Hertford who went to London to take an apprenticeship as a silversmith. Later, he became a sculptor and found calotype photography useful as a way of capturing images of his sculptures. Dissatisfied with the poor definition and contrast of the calotype and the long exposures needed, Scott Archer invented the new process in 1848 and published it in The Chemist in March 1851, enabling photographers to combine the fine detail of the daguerreotype with the ability to print multiple paper copies like the calotype. In publishing his discovery, he did so knowingly without first patenting it, giving it as a gift to the world.
This process originally called the wet-collodion process, or simply the collodion process, and as we call it today the wet-plate collodion process. This process involves adding a soluble iodides & bromides to a solution of collodion (cellulose nitrate) and coating a glass plate with the mixture. The plate is then immersed in a solution of silver nitrate to form silver halides. The plate, still wet, is exposed in the camera. It is then developed by pouring a solution of pyrogallic acid or ferrous sulfate over it and then is fixed with a strong solution of sodium thiosulfate, for which potassium cyanide was later substituted. Immediate developing and fixing were necessary because, after the collodion film had dried, it became waterproof and the reagent solutions could not penetrate it. This process was valued for the level of detail and clarity it allowed. A modification of the process, in which an underexposed negative was backed with black paper or velvet to form what was called an ambrotype, became very popular from the mid- to late 19th century, as did a version of black lacquered metal known as a tintype, or ferrotype.
The Silver Sunbeam list 10 different steps to process a single positive wet collodion photo. Those Steps are described as follows:
- Preparation of Glass: A piece of glass is thoroughly cleaned, sized and polished. This step is skipped for tintypes.
- Coating with collodion: While holding the plate in a horizontal position the collodion is flowed onto the plate to make a smooth and even coating on it.
- Sensitizing it: The coated plate is then placed into a bath of silver nitrate for several minutes to sensitize it.
- In darkroom conditions, the plate is removed from the bath and placed into a lightproof box, called a plate holder. the plate holder is carried to the camera, locked into place with the dark slide facing the lens.
- Exposing it in the camera: The dark slide is removed; we are ready to take the photo. The exposure times vary based on the lens, light, weather and the chemicals, but is generally just a few seconds. This is done by removing the lens cap and replacing it.
- The plate holder is closed up, and taken back to the darkroom.
- Developing the picture: Back in the darkroom the plate is then removed from the plate holder and developed out by pouring a developer solution over its surface. When the plate is judged to be fully developed, it is stopped from developing any further and rinsed using clean water
- Fixing the image: Out of the darkroom the plate is then fixed by placing it into a chemical solution sodium Thiosulfate, generically called Hypo or Fix which dissolves the remaining unexposed silver, and prevents the silver from further darkening. Permanently fixing the image. It is then thoroughly rinsed in clean water.
- Drying the plate: The plate is then dried either by air or by use of a small alcohol burner flame.
- Coloring: The image is then hand-colored to give life to cheeks, or color to curtains, and so on. (this step is typically omitted)
- Varnishing: The plate is then warmed and varnished to protect the image.
- Backing: Then finally for ambrotypes. The plate is coated with asphaltum or provided a backing made from paper, velvet, or an unused tintype.
For the different solutions, we use modern adaptations of historic recipes, we choose not use potassium cyanide as our fixer to avoid the potential risk associated when working with the public. The chemicals used in modern wet-plate photography are considered ORMD and are still considered as toxic if not treated with respect for what they are.