BLACK AND WHITE FILM DEVELOPING [Film Technology]

BLACK AND WHITE FILM DEVELOPING 
[Film Technology]

The process of image formation can be much amplified by the use of a developing agent. This is a chemical reducing agent that act as donating electrons to positively charged silver ions in the emulsion and converting them to metallic silver. This reaction takes place most rapidly around the tiny particles of silver in development centres that have already formed during exposure. The silver may be thought of as acting as a catalyst for the reaction, and exposed crystals are developed up to two hundred times faster than unexposed ones. The reaction of development may be as Ag⁺br^-₊(dev)->Ag₊(dev)⁺+Br^- The initial developing agent and silver bromide react to produce grains of metallic silver which, being insoluble, remain in the film emulsion, and oxidized developing agent and bromide ions, both which pass into solution. Thus the exposed areas of the film are visibly darkened by the formation of metallic silver. The image can be made permanent by passing the film into a fixer solution, which dissolves away the unwanted silver bromide.

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