Response to chemicals used in photo development

Let's assume you mean normal black and white photography. The photographic emulsion consists of a component called silverhalides. These silverhalides (halides are the common name for bromides, iodides, chlorides, fluorides) are sensitive to light. When making a picture, light sensitives the silverhalide. The first chemical needed to develop the print is obviously the developer. This developer is mostly a very complex chemical (e.g hydroquinone=1,4-dihydroxybenzene;), because it can change (read develop) ONLY the sensitivised silverhalide. The developer changes thus the sentised silverhalide into metallic silver. This process forms the image. The next step is ending the action of the developer. All developers are alkali, so an acid is used to stop the development (hence stop bath)Mostly an organic acid as citric acid (2-Hydroxy-1,2,3,-propanetncarboxylic acid)is used in dilution to do the job. The last bath is the fixing bath. This bath reacts with the remaining (not developed) silverhalide in the emulsion of the print, in order to remove that silverhalide. The final result is that only the metallic silver remains in the picture. The chemical compount to do this is called a fixer, nowadays mostly AMMONIUM THIOSULFATE.

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