Rehalogenating bleach: The great reset button?

Boggy1 · Dec 2, 2010

From my limited understanding of photography (please correct me if I'm wrong!), when you reversal develop black and white film, you do not use Potassium Ferricyanide as your bleach. I think that this is because it is a rehalogenating bleach, which will "reset" the silver, making the exposed grains indistinguishable from the unexposed grains.

What would happen if I accidently exposed a roll of film or a pack of paper to copious amounts of light? Would it be possible to use this to my advantage and "reset" the film by using Potassium Ferricyanide?

Thankyou for your time.

Photo Engineer · Dec 2, 2010

You cannot reset the film. There are chemicals in the film that are washed out by this treatment and the loss of these chemicals will just about destroy the quality of the film and its speed.

PE

Boggy1 · Dec 2, 2010

This has just gotten me more interested!

Do you know what way the film could be affected? I suppose that one of the important chemicals that could be washed out are the dyes used to sensitize the film to red and green. . . perhaps I could make myself a make-shift orthochromatic film this way! Or maybe the anti-halation coating could be washed off, giving me interesting halos and artifacts on and near my highlights. I suppose that to try this out, I wouldn't need Potassium Ferricyanide, but rather just plain old water.

Ian Grant · Dec 2, 2010

Films can't be revived except as slow emulsions with little or no red sensitivity for the reasons Ron's given. You also need an excess of halide present along with the Ferricyanide.

Papers can be revived (but not restored to as they were) but it's not quite as simple as a re-halogenating bleach, bathing in additional baths can help improve speed and contrast slightly. An number of chemicals can help, Sodium S|sulphite is one that I've seen recommended and in fact tried.

It's possible to convert fogged paper into POP, however it really depends on the type and severity of the fogging and the paper.

Ian

Photo Engineer · Dec 2, 2010

Well, as Ian noted, you will destroy the spectral sensitivity and have only a blue sensitive emulsion with very low speed. You will destroy the specific crystal habit and halide balance of the emulsion thereby destroying speed and contrast. Finally, you will wash out acutance dyes thereby making the film less sharp and more prone to flare.

You will destroy latent image safeguards, raw stock keeping chemistry, reciprocity safeguards and generally ruin keeping and over/under exposure quality.

So, you will end up with about an ISO 1 film (if you are lucky) that has no keeping, lots of flare and is not very sharp. It will be cranky to work with and have a weird curve shape.

This is just for starters.

PE

Jordan · Dec 2, 2010

Even if you wanted to "reset" the film, I don't think a rehalogenating bleach is what you would want to do it. There is very little reduced silver to bleach in an exposed-but-undeveloped silver halide emulsion.

Hexavalent · Dec 2, 2010

Photo Engineer said:
So, you will end up with about an ISO 1 film (if you are lucky) that has no keeping, lots of flare and is not very sharp. It will be cranky to work with and have a weird curve shape.

PE

And all this time I've been making my own to those specs, when I could have just bleached film!

Boggy1 · Dec 3, 2010

Wow- I really didn't expect so many replies!

Well, Ian Grant, Photo Engineer; thanks for your advice. I guess that leaching out all the fancy chemicals and such in film leaving me with only a very basic emulsion would be a great project; as long as I find a way around the whole it loosing its ability to be under/over exposed. I can't even imagine how to meter for an iso of just 1! I'm sure that trying all this on paper would be a great starting point though; even though I can imagine that being just as "cranky". I'm probably getting into all this at a level that's far too advanced for me, but I'd love to try this all out as a project as soon as I get a chance! (I'm hoping for some photographic supplies for christmas!)

Jordan, if I do want to reset the film, do you have any ideas of what I could use? I understand that this would be extremely tricky, requiring many different chemicals and baths, as Ian Grant and Photo Engineer explained, I guess I could try and be more "gentle" on the film if I apply all this using a pastry brush.

And finally, Hexavalent, rock on with your emulsions!

(I'm sorry for my post being so incoherent! I'm not very experienced with netiquette)

bdial · Dec 17, 2010

So, if you were starting, for example, with unprocessed antique glass plates, which (presumably) would be slow to begin with and mostly blue sensitive, how might one go about rejuvenating the emulsion to some usable state? A re-halogenating bleach, plus what else?

Photo Engineer · Dec 17, 2010

Do you know what Kotavachrome was?

Anyhow, bleaching silver halide using a rehal bleach removes all sensitivity from the emulsion, removes all grain structure, and creates an amorphous silver halide with no discrete structure and no definable sensitivity. The sensitivity depends on local halide and other impurities and your given bleach and process. It is what it is.

Sorry

PE

bdial · Dec 17, 2010

I've been aquiring antique materials lately, the avatar is my box labeled "Kotava Positive Film, Vitava Opal Speed". My google search indicated it was a positive material coated on an ivory base and meant for hand coloring.

Not sure why that would be useful, but Kodak did at one time, apparently.
That particular box is still sealed, but I'm not sure I'll try doing anything with it. I know that age fog is as likely to have ruined it as anything else. But, I liked the graphic nature of the label, so I made it my avatar.

The question was in reference to an opened box containing 3 4x5 plates I just got, with early kodak labeling, it says "Eastman 40" on the side with emulsion # A459, but no dates. The box was incorrectly assembled, so it seems likely the plates are light struck. I thought it would be interesting to try anything that could result in an image.

Thanks for the reponse though.
Barry

Photo Engineer · Dec 17, 2010

Barry;

The Kotavachrome was the print material used to make reflection prints of the original Kodachrome slides. It was to be replaced by a product called Azochrome. When the Kodachrome process changed from the original process to the current one involving exposure through the base, the old process would never work on a reflection material.

I have a roll of the support here given to me by Grant Haist. It looks like white plastic, similar to that which is used for Ilfochrome.

As for the plates, they are probably more valuable as is rather than doing something like trying to rehal them into usefulness.

PE

Hologram · Dec 18, 2010

Boggy1 said:
Jordan, if I do want to reset the film, do you have any ideas of what I could use? I understand that this would be extremely tricky, requiring many different chemicals and baths, as Ian Grant and Photo Engineer explained, I guess I could try and be more "gentle" on the film if I apply all this using a pastry brush.

Maybe it's not that complicated.
To some extent, Lippmann/holographic AgX emulsions can be "reset" as you put it. How far such methods could be applied to plain photographic emulsions remains to be seen though. But it's definitely worth a try.
Using a very mild rehalogenating bleach (20g ferric EDTA + 10g KBr/L) may already do the job (by the way, ferric rehalogenating bleaches do not destroy the sensitizing dyes). Bathing the film in 10g/L ascorbic acid (or 10g Metol +2 sodium carbonate/L) may reactivate the emulsion.

Photo Engineer · Dec 18, 2010

Make sure it is Sodium Ferric EDTA and not Ammonium Ferric EDTA, otherwise you will also fix the film or plate.

PE

John Shriver · Feb 25, 2011

Eastman 40 plates are non-color-sensitized, daylight EI 32 (Weston/GE), tungsten EI 8, develop in DK-50 (1:1) for 10 minutes at 68°F.

General Treegan · Jun 16, 2023

Years passed but I still want to share the results of using copper bleach as a "reset" film and paper for experimental work.
The image is a piece I cut from an old X-ray sheet, already used, so already developed and sent back to a light-sensitive state using copper bleach and then exposed by contact with a leaf, developed and fixed.

Rehalogenating bleach: The great reset button?

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