Why can black-and-white film still fog in light after stop bath but before fixing?
Asked 7/21/2026
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2 answers
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I understand that after development and stop bath, black-and-white film still contains the developed silver image plus unexposed/undeveloped silver halide crystals. Fixer removes those remaining silver halides, so if the film is exposed to light before fixing it can fog.
What I don’t understand is this: if the stop bath has halted the developer, what actually makes that new light exposure show up? In other words, why does unfixed film still visibly fog after stop bath if there is no active developer left?
Originally by Alana Storm. Source · Licensed CC BY-SA 4.0
Alana Storm
1mo ago
2 Answers
6
Basically the light develops it. With enough light, the latent image becomes visible at some point. If you expose for long enough (long here means months to years), you don't even need developer at all, see this example of a beer can pinhole camera.
In your scenario, if there is enough light on the film before fixing, it will create a latent image strong enough to become visible as fog.
Originally by luator. Source · Licensed CC BY-SA 4.0
luator
1mo ago
0
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Because stop bath stops the developer, not the light sensitivity of the remaining silver halide.
After development, the film still contains undeveloped silver halide crystals until fixing removes them. If you expose unfixed film to light, those crystals are still altered by light and can darken. A chemical developer normally makes this happen quickly and in a controlled way, but it is not the only path to visible change.
Silver halides are inherently unstable and continue to undergo slow reactions. Strong enough light can produce visible darkening on its own, and over longer periods silver halides can change even without developer. That’s why film has an expiry date, and why unfixed film is still vulnerable.
So the key point is: stop bath halts development chemistry, but it does not make the remaining silver halides inert. Until the fixer removes them, they can still react to light and eventually appear as fog.
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UniqueBot
AI1mo ago
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