The primary chemical name for the fixer used in the photographic process, often referred to as "photo washing" or "fixing," is sodium thiosulfate.
Understanding "Photo Washing" in Photography
In the context of traditional black and white photography, the term "photo washing" can refer to several stages where liquids are used. However, when seeking a specific chemical name for a washing process that makes an image permanent, it points directly to the fixing stage. During this crucial step, the developed photographic film or paper is treated with a chemical solution to remove unexposed silver halides. This process ensures the image is stable and no longer sensitive to light, preventing it from fading or turning dark over time.
This chemical solution is commonly known as fixer or Hypo solution. The reference confirms that in black and white photography, the developed film is "fixed by washing," highlighting the connection between the "washing" action and the fixing chemical.
Sodium Thiosulfate: The Key Chemical
The active chemical compound in fixer is sodium thiosulfate. It can also be referred to by its older name, sodium hyposulfite.
- Chemical Name: Sodium Thiosulfate
- Common Names: Hypo, Fixer, Sodium Hyposulfite
Function: The main function of sodium thiosulfate is to dissolve and remove any residual silver halides that were not exposed to light or developed into a visible image. These silver halides, if left on the film or paper, would continue to react with light, eventually blackening the entire image and causing it to degrade.
Why Fixing is Crucial
The fixing stage, facilitated by sodium thiosulfate, is indispensable for the longevity and quality of photographic prints and negatives. Its importance can be summarized as follows:
- Image Permanence: It makes the photographic image stable and permanent by removing light-sensitive silver compounds.
- Clarity: It clears the unexposed areas, allowing light to pass through negatives correctly or ensuring white areas on prints remain clear.
- Archival Quality: Proper fixing and subsequent washing are vital for achieving archival quality, meaning the photographs will last for many decades without significant deterioration.
Summary of Key Photographic Chemicals (Fixing Stage)
| Term | Chemical Name | Purpose |
|---|---|---|
| Fixer (Hypo Solution) | Sodium Thiosulfate | Removes unexposed silver halides to make the image permanent. |
| (Alternative Name) | Sodium Hyposulfite | Another name for the active chemical in fixer. |
| Photo Washing (Fixing) | Sodium Thiosulfate | The process of treating developed film/paper with fixer. |
In summary, while "photo washing" can broadly refer to any liquid treatment in photography, the specific chemical associated with a critical "washing" step that ensures image permanence is sodium thiosulfate, used in the fixing process.
