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When I develop C-41 on Kodak 120 rolls the washwater from the first soak has a strong purple or green color. I am wondering what causes this color and if I can flush it without environmental concerns. I don’t have this on 135 or large format. And only on Kodak branded colorfilm. I wash at 38c

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The light sensitive goodies in all emulsion layers are various salts of silver. In their natural state they are only sensitive to violet and blue light. These have been modified to increase their sensitivity into the green and red regions of the spectrum. This is done by inducing sensitizing dyes into the mix. These dyes plus a back coat (antihalation coat), made with dye is designed to protect the film from secondary exposure from the rear. Halations are unwanted reflections caused by light traversing the emulsions and then hitting the pressure plate and/or junction emulsion to film base and reflecting backwards into the film. A halo-like circle will surround bright areas. This layer stops this action.

All these dyes are water soluble and like all the other chemicals and residual stuff are reasonably benign.

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  • Thank you Alan! I didn’t realize the anti halation side; I thought this was done by the matt-black backing where the 120 roll is wrapped in.
    – CaptainAhab
    May 9, 2021 at 17:53
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    @CaptainAhab, FYI, 220 rolls have exactly the same film as in a 120 roll, but without any paper backing: There's a paper leader at either end, but in between the two ends, there's nothing but film.
    – Solomon Slow
    May 9, 2021 at 21:27
  • Movie film and some 35mm still camera film have a Removable Jet Black Backing (Remjet). Lamp black in an acid plastic that is removable with a mild alkaline bath. Prevents light from exposing the film from the rear. This is light that might enter the camera via the viewfinder system should the eye be removed during filming.
    – Alan Marcus
    May 9, 2021 at 22:02
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    Why does the colour only appear for the OP with 120 film? Why not with 135 or large format?
    – osullic
    May 9, 2021 at 22:07

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