Why does Kodak 120 C-41 film release purple or green dye in the first rinse?
Asked 5/9/2021
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When processing Kodak 120 C-41 film at 38°C, the water from the first rinse/soak sometimes comes out strongly purple or green. I don’t see this with 35mm or large format, and it seems to happen only with Kodak-branded color film. What causes the color, and is it generally safe to wash it down the drain?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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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.
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
5y ago
0
Generated from our catalog & community — verify before relying on it.
The purple or green color is typically dye washing out of the film, not something unusual going wrong in processing. Color films contain sensitizing dyes in the emulsion and often an antihalation backing/coating that helps prevent internal reflections and halos. Some of these dyes are water-soluble and can come off in the first rinse or presoak, especially with certain Kodak 120 films.
The fact that you see it more with 120 than with 35mm or sheet film is consistent with differences in film construction and backing layers between formats. So the colored rinse is generally normal.
As for disposal: this initial colored rinse is mostly dye and wash water, and is generally far less of a concern than spent developer, bleach, fixer, or bleach-fix. The bigger environmental issue in film processing is silver-bearing chemistry, especially fixer or blix. If you want to be cautious, follow your local disposal rules for photo chemicals, but the colored first rinse itself is not usually the main problem.
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