Response to Have I over-developed my film?

The film does not turn from opaque to transparent--what really happens is that the exposed part of the film turns opaque and the rest of the unexposed portions of the emulsion get removed by the fixer, leaving the clear areas on the developed film. Basically, development converts silver halides to pure silver, which then appear as black flecks in the film emulsion (the opaque part of the developed film). When you over-develop you convert more halides to silver, so you get blacker black areas. Also when you over-develop, sometimes the development action is so vigorous that it carries over to unexposed silver halides; this is known as contagious development and results in "fog", or black areas that should be clear.

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