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I am taking analog photos, mostly on color reversal film. Sometimes, I want to locally reduce color within a frame, preferably to pure black and white.

Is there a method to drastically reduce color saturation within an otherwise color photo on film?


This question is no longer a duplicate since it has been edited to emphasize how to achieve a desired effect (desaturation of portion of image) rather than method of achieving effect (physical filter). While likely not possible with filters, it may be possible with a modified bleach bypass process or other method.

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    Suppose such a filter exists. It would necessarily reduce the amount of light passing through it. The affected portion of the frame would be underexposed (or the unaffected portion overexposed). However, you might be able to accomplish what you want by selectively applying bleach to the film during the development process. This would cause part of the image to be formed by silver particles (black and white), while the rest would be formed by dyes (color). Perhaps one of the film shooters can explain further. – xiota May 22 at 19:52
  • ohhh very interesting idea. Do you think the dyes could be washed off with the bleach after the development process is completed? Becaus I'd have to see the picture to know where to apply it. – Jeffrey May 22 at 20:06
  • I don't know when in the process it's okay to expose the film to light, and when the image becomes visible. The steps for reversal film are also different from what I'm familiar with (black and white and C41). You can look more into bleach bypass for more info. It might be possible to apply bleach after bleach bypass. – xiota May 22 at 20:36
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Fully developed color film contains no silver. Bleach in the process converts developed silver into soluble silver that is then removed by the fixer. What remains in the film is cyan, magenta, and yellow dyes. These create all color and density you see. Applying a bleach for the dyes to film post processing will result in fading of the image, not desaturation. Greys in color film are a result of equal amounts of the three colored dyes. This is called a chromagenic grey.

If you desire a neutral grey, this would be an additive process not a subtractive one. proper amounts of retouching dyes, painstakingly applied to the film to shift colors towards grey. So if an area of the film is red, cyan would need to be added to that area to bring the color to neutral grey. Because it's additive, it would also increase density in the area.

Such a feat on camera film would be incredibly difficult. When we used to retouch on film, a large format inter-positive would be made. Essentially an 8x10 11x14 or 16x20 "slide". The larger format would make retouching possible.

A more feasible direction would be to shoot the image in black and white then hand tint the areas to add color, much in the way old black and white prints would be colored by hand. This could be done directly on film using retouching dyes - if you can find them, or on black and white prints using Marshall Photo Oils and Marshall Pencils that are specifically made for the purpose.

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Photographers had lots of tricks up their sleeve. We made masks. We would contact print a negative or slide using black & white film. We could make a negative or a positive mask. This makes a faint black & white image, either negative of positive. We sandwiched the mask and the slide together and made a print or duplicate slide. The mask was carefully made and used to control contrast and saturation. A positive mask bolsters the densities, a negative mask flattens. These methods were prevalent when the film used was 4x5 or 8x10 in size and likely not applied to 35mm size film. The exception is, the making of release prints for the motion picture theater. Cine printing became so sophisticated, masks were commonplace. Some were called “flying masks” because they created an illusion that the principal subject was a superman flying over Metropolis, while he was actually photographed in the studio (no green screen in that era).

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