The Process

Whether processing at an amateur or commercial level, the film is treated in chemical baths. Each of these baths is closely monitored and maintained at a specific temperature and treatment time. Developer baths are most sensitive to deviations from the standard processing conditions (e.g., time and temperature); other baths are less sensitive.

• The developer, which turns the latent image to metallic silver.
  
  
• A stop bath, which stops the action of developer, typically a dilute solution of acetic acid. In modern automatic processing machines, this step is replaced by mechanical squeegee or pinching rollers. In small scale darkrooms, stop bath may use citric acid or other organic acids, or simply plain water. Any of these treatments removes the bulk of the carried-over alkaline developer, and the acid, when used, neutralizes the alkalinity to reduce the contamination of the fixing bath with the developer.
  
  
• The fixer makes the image permanent and light-resistant by dissolving any remaining silver halides. The fixer is sometimes referred to as "hypo," a misnomer originating from casually shortened form of the alchemist's name hyposulphite. None of "hyposulphite," "hyposulfite" and "hypo" is used to mean thiosulfate in modern chemistry.
  
  
• Clean water wash to remove any fixer, as residual fixer can deteriorate the silver image, leading to discoloration, staining and fading. The washing time can be reduced and the fixer more completely removed if a washing aid (also known as hypo clearing agent, or HCA) is used after the fixer.
  
  
• An optional final immersion in a film conditioner. This is a solution of a non-ionic wetting agent in water which helps uniform drying and eliminates drying marks from hard water.
  
  
• Film is then dried in a dust-free environment, and finally cut (if roll film) and put into protective sleeves.