In photography, the terms “developer” and “fixer” refer to essential chemicals used in the process of developing film and prints in traditional darkroom photography. These chemicals play distinct roles in the photographic development process. Let’s delve into the science behind different kinds of developers and fixers in photography.
Developers are chemicals used to convert the latent image, formed when light interacts with photosensitive silver halide crystals on photographic film or paper, into a visible image. This is achieved by conversion of silver halides into silver metal. There are several types of developers, each with unique characteristics and properties:
- Types of Developers:
- Black and White Developers: These are primarily used in black and white photography. There are two main types: liquid and powder developers. The developer consists of a reducing agent (such as Metol or Hydroquinone) and an alkali to provide an alkaline environment.
- Color Developers: Color photography involves the use of color developers. In color film, developers are specific to the emulsion layers, and the process involves the development of three-color layers (red, green, and blue).
- Function of Developer:
- Developers work by reducing exposed silver halide crystals to metallic silver. The unexposed silver halide remains in the emulsion and is subsequently removed during fixing.
- Development Process:
- When the exposed film is immersed in the developer solution, the developer reduces the silver halide crystals. As a result, metallic silver particles form at the exposed regions. This creates the visible image on the film or paper.
- There are different types of developer solutions, including: metol, phenidone, dimezone , and hydroquinone.
- Some commercially available developers are –
D-76: A common black and white film developer known for its versatility and wide usage.
X-Tol: Another popular developer for black and white film, known for producing fine grain and sharp images.
HC-110: A highly concentrated liquid developer for black and white film, known for its flexibility and long shelf life.
After the image has been developed, the photographic material still contains some unreduced silver halides that need to be fixed to prevent further light sensitivity. This is a way of preserving the image because if these grains are not removed, they can continue to be reduced by sunlight and degrade the image.
Fixer is the chemical used for this purpose. It dissolves the unexposed silver halide, leaving only the developed metallic silver on the film or paper. They serve the following important functions:
- Removal of Unexposed Silver Halide:
- Unexposed silver halide crystals are still sensitive to light and can lead to further darkening of the image over time. Fixers remove these crystals to prevent any further exposure.
- Permanent Image Fixation:
- Fixers make the image on the film or paper permanent by removing the unexposed silver halide. This prevents the image from deteriorating and also makes the material insensitive to further exposure to light.
- Fixing Process:
- In the fixing process, the photographic material is immersed in a fixer solution. The fixer contains a complexing agent (usually sodium thiosulfate) that dissolves the unexposed silver halide crystals, leaving only the developed, metallic silver image behind.
- Sodium Thiosulfate (Na2S2O3) – This is a common fixer chemical used in traditional darkroom processes. However, it is considered to be an outdated fixer due to its slow fixing time. Fast fixers are used now a days to speed up the fixing process.