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When black and white photo film is completely overexposed and developed, will it be completely black opaque (you can't see light through) or will it be black but not opaque (you can see light through)? and why is this so?

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    It will really depend upon where one places the threshold that defines completely overexposed. In other words, your question is mostly about semantics. It will also depend upon exactly how bright the light you can or can not see through the film is. It could also depend upon the density of the film grains in a particular film emulsion.
    – Michael C
    Feb 14 at 17:40

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Fully exposed (i.e. sitting out in room light to the limit of the H/D curve) B&W film that's fully developed is not completely opaque. Many years ago, this was recommended as a filter for viewing the sun's disk and solar eclipses (there are better, safer filters now, please don't try this) -- because you could see the sun through the film.

This is film at the highest density obtainable. Still not completely opaque.

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  • But this means that when using the photo enlarger for developing photos you could take a completely overexposed negative and develop it and you could get a brighter (whiter) photo instead of a completely black photo although the negative is completely overexposed?
    – Sebastyen Laroche
    Feb 14 at 20:30
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    Yes, you can make a print of whatever degree of black or white you wish by putting more light through the negative, either with a brighter bulb/larger aperture, or a longer exposure, or both. For a completely overexposed negative you will not be able to print an image- you've surpassed the limits of the medium.
    – BobT
    Feb 14 at 22:03
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    An overexposed negative would generally produce an overly white print -- except that in making an enlargement you generally adjust your exposure to get a "normal" looking print. Expose the print longer and you get a darker print, though with a maximum density negative this will take a long time with most enlargers. Not sure why you'd bother, though; that negative doesn't have an image on it, and you could get the same print in a tiny fraction of the time by taking the negative out of the enlarger...
    – Zeiss Ikon
    Feb 14 at 22:08
  • It is perhaps worth noting, that leaving film out in room or day light and then (fully) develop it, will not yield the maximum obtainable density. If film is extremely overexposed, the solarization effect will kick in and reduce the density.
    – jarnbjo
    Feb 15 at 10:32
  • @jarnbjo Most modern emulsions will not solarize the way they did in (for instance) Ansel Adams's "Black Sun" -- that extreme shoulder, if it exists in any current film, would be found only in those still using 1950s or earlier emulsion technology like Svema 64 or maybe Kodak's Double-X.
    – Zeiss Ikon
    Feb 15 at 12:01

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