Developer

• The initial and most important chemical used in film processing is the developer. When film is exposed to light, sensitive silver halide particles react with the emulsion, forming the silver ions of the latent image. Developer further reacts with these ions, transforming them into black silver and leaving behind the silver halide crystals that were not affected by the light.
  
  

Stop Bath

• This chemical does exactly what its name says---it stops the film from further development. Stop bath neutralizes the developer, which can turn images too dark if the process is allowed to continue. Water can also be used to stop development, although the process takes longer. Stop bath's effect is almost instantaneous.
  
  

Fixer

• Developed film does not retain a permanent image until it is exposed to fixer. This solution has agents that remove remaining silver halide particles and hardeners to protect the film emulsion. Fixer also has an acidic pH, which counteracts the developer's alkalinity.
  
  

Washing

• The final step in film processing is washing all traces of chemical from the emulsion before hanging it to dry. Water can accomplish this, but often a solution called hypo is added to speed the process.