At a glance
| Invented | 1851, Frederick Scott Archer |
| Support | Aluminum (tintype), glass (ambrotype, negative) |
| Silver bath | Silver nitrate, approx. 9% |
| Sensitizing | approx. 2–3 minutes |
| Exposure | seconds to minutes, depending on light |
| Special feature | Plate must be exposed and developed while wet |
| Result | One-off, no copies possible (except negative) |
What is the wet collodion process?
In the wet collodion process the image is created directly on a plate of glass or metal. The plate is coated with collodion, sensitized in a bath of silver nitrate solution and exposed while it is still wet. It is then developed immediately.
The name comes from exactly this urgency: if the layer dries, it loses its sensitivity. That is why a darkroom is needed right next to the camera, in the studio or as a mobile tent.
History
Frederick Scott Archer introduced the process in 1851. Compared with the daguerreotype it significantly shortened exposure times and was cheaper. It became the most important process for portrait photography and shaped photography until the 1880s.
The chemistry
Four solutions determine the image. Their recipes differ from photographer to photographer and are part of one’s signature. Unfortunately, hardly any records survive of which recipes individual photographers used, but I still work with recipes that were used at the time and were publicly available.
Collodion
Nitrocellulose dissolved in alcohol and ether, with iodide and bromide salts. This syrupy layer holds the image.
Silver bath
Silver nitrate in distilled water, about 9%. Light-sensitive silver halides form in the bath.
Developer
An iron-based developer makes the latent image visible.
Fixer
Dissolves the unexposed silver halide. Only now does the image become bright and permanent.
Silver nitrate is a strong oxidizer, ether highly flammable. If you work yourself, wear gloves and goggles and ensure ventilation. More in the article Silver bath maintenance, part 1.
Step by step
- Preparing the plate – Glass is cleaned thoroughly, aluminum is usually already lacquered.
- Pouring the collodion – The solution is poured on and spread evenly by tilting.
- Sensitizing – In the silver bath the plate becomes light-sensitive in about 2 to 3 minutes and then looks milky.
- Exposing wet – In the plate holder into the large format camera. Depending on light, a few seconds to minutes.
- Developing and fixing – In the darkroom the image appears, in the fixer it turns bright: the magic moment.
- Washing, drying, varnishing – A protective varnish seals the plate and makes it durable and archival.
Tintype, ambrotype, glass negative
All three are made with the same process. The difference lies in the support and whether the image is a positive or a negative.
| Tintype | Ambrotype | Glass negative | |
|---|---|---|---|
| Support | Aluminum | Glass | Glass |
| Result | Positive, one-off | Positive, one-off | Negative for prints |
| Look | warm, metallic sheen | delicacy and depth | master for salt, albumen, collodion chloride paper |
| Also called | Ferrotype | Glass image | Collodion negative |
Frequently asked questions
Is every image unique?
Yes. Tintypes and ambrotypes are direct positives. There is no negative and therefore no second copy.
Why does blue look light and red dark?
Collodion is mainly sensitive to blue and ultraviolet light. Red is barely recorded and appears dark.
How long does a collodion image last?
Hundreds of years, provided the plate was washed thoroughly after fixing. A collodion image is then extremely archival.
Experience it yourself
Portrait: Have your own tintype made
Workshop: Learn the process in one day