I've recently been reviewing what's changed in film processing in the decade or so I've been away from it.

One of the things I found in YouTube videos is that apparently there's now a way to process B&W reversal without requiring toxic, strongly acidic bleach solutions (potassium permanganate or potassium dichromate and sulfuric acid) -- this "new" process uses a solution of hydrogen peroxide acidified with either citric acid or acetic acid, or a two-bath treatment going from straight peroxide (anywhere from 3% to 35%, apparently, depending how much of a hurry you're in) to the acid bath and back again for several cycles.

Note that this is not a rehalogenating bleach like those used in color processes; it actually removes the developed silver from the film without affecting the undeveloped halide (and, apparently, can redeposit the silver complex it forms if the solution stands on a horizontal emulsion, leading to silver staining on prints if bleached face up).

On the face, then, it seems as though this bleaching process, with a separate fixing step, ought to work on C-41 or E-6 films in place of the usual EDTA based rehalogenating bleach -- except that I recall hydrogen peroxide as being a strong bleach in another sense, that of denaturing organic color pigments and dyes, like the ones that form the color image in color negative or positive films. That, of course, would defeat the purpose of using the bleach on the film.

Has anyone tried a peroxide based bleaching process on color films? Does it damage the dye images, or are they impervious to the oxidizing action of the peroxide?

  • \$\begingroup\$ You might try asking this question on the Large Format Photography site. They have a darkroom processing forum that could probably answer your question. \$\endgroup\$
    – BobT
    Mar 14, 2020 at 17:37
  • \$\begingroup\$ I'm a member there since around 2003, though not very active the past ten years. I'll try asking there and on Photrio (formerly APUG) where I'm also a member. \$\endgroup\$
    – Zeiss Ikon
    Mar 16, 2020 at 11:01
  • \$\begingroup\$ I'm starting to think I'll have to get some 12% peroxide and test this myself, and self-answer. I'm sure it isn't that no one has done this; but the intersect of photographic experimenters like those we see on YouTube, and active members of Photography.SE may be a null set... \$\endgroup\$
    – Zeiss Ikon
    Aug 18, 2020 at 14:58

1 Answer 1



I don't know if I have my old Kodak film documentation, but one reason peroxide would not have been chosen was it's reactivity- it decomposes too fast to be useful for manufacturing. Add in heavy metal contamination and certain explosive concerns, it would never have made it out of the gate at Kodak.

The bleaching process is just that, though- the chemicals picked are to do the work while moving ions around.

I'll have to dig up the old formulation guides. I seem to remember several other old books though that discussed alternatives to B&W chemical reversal film, and their chemical preparation. Darned if I can remember their name- they were all typed and spiral bound and at least from the 60s, and included several formulations of developer.

  • \$\begingroup\$ Not much explosion risk with 3% drug store peroxide, though heavy metals might be present as stabilizers. I can buy gallon quantities of 12% pretty easily, and 35% if needed -- the latter two in food grade! -- but I'd rather not handle peroxide at 35% if I don't need to. \$\endgroup\$
    – Zeiss Ikon
    Mar 20, 2020 at 19:44
  • \$\begingroup\$ 3% would never get shipped in manufacturing- the amount you'd need to send to a photo lab.... would be tremendous. Just put it out there for folks to remember that H2O2 isn't just water. Edit: And 35% is getting more regulated, as it's the poor mans IED. So finding it contaminated wouldn't surprise me at all. \$\endgroup\$
    – J.Hirsch
    Mar 20, 2020 at 19:46
  • \$\begingroup\$ Sure. I'm trying to find an alternative to chemicals that are no longer easy to buy, and that means starting with known bleaches for silver images -- ferricyanide rehalogenating (works in color, not in B&W reversal) and peroxide (known to work in B&W reversal, unclear what it would do to color dyes). \$\endgroup\$
    – Zeiss Ikon
    Mar 20, 2020 at 19:47
  • \$\begingroup\$ @ZeissIkon I'll get looking. Might be helpful reads: s3.cad.rit.edu/ipi-assets/publications/… kodak.com/uploadedfiles/motion/… \$\endgroup\$
    – J.Hirsch
    Mar 20, 2020 at 19:56
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    \$\begingroup\$ What’s in a name? The old standby, Potassium Ferricyanide, has been used for maybe 100 years or more without incident as film bleach. The cyanide is so tightly bounded, it can’t get free thus it is suitable (in fact the preferred film bleach). The name is forbidding and the cyanide can be liberated, with difficulty. By the way, it is used in foods, particularly as an anti-caking agent in table salt. Kodak turned to EDTA (Ethylenediaminetetraacetic acid). It is a sequent used in foods like French Dressing and as a medicine to treat heavy metal poisoning. Both are reasonably benign. \$\endgroup\$ Aug 18, 2020 at 15:12

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