Once film has been exposed, it must go through a series of chemical processes to bring out the image. The first step is known as development , and developers such as hydroquinone, catechols and aminophenols are used. Development is stopped by putting the film in a stop bath , which usually contains a solution of dilute acetic or muriatic acid. Next, fixers are used to remove any unreacted silver halide from the film. The primary ingredient in a fixer solution is usually either sodium or ammonium thiosulfate.
Washing finishes the treatment process by removing any contamination from previous treatments.
Finally, the film is dried. Many of the chemicals used in film processing can be toxic or hazardous to human health if used or disposed improperly. For example, acids used in developing film can burn and blind you. Do not dispose of these solutions in your septic system. Ask a friend or relative who is connected to a sanitary sewer system if you can dispose of your diluted solution down their drain.