Black and white reversal film, safer bleaching
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We are. Cerium it's not an alternative imho, it's too expensive and too slow acting.
In #1 it's apparently used as an accelerator for the primary ferrous bleach. This is in line with existing patent information from Fuji.
Fuji admitted the cerium slow acting problem but didn't further address it because of the lost interest in b&w reversal context. Tmk there are no recent papers about this.
If it was a viable alternative Adox and Fuji could have been implementing them, but no. They both use permanganate as bleach.
Fuji didn't say that permanganate damages the subbing layer. The primary and only reason Fuji did the patent is environmental: "Of these compounds, a heavy metal compound such as permanganate or bichromate, and a compound having a cyanide ion such as ferricyanide are not preferably employed because they can be harmful to animals and plants when they occur in waste water, etc."
Cerium isn't used as an accelerator: it isn't an accelerator. It's an oxidizer.
Bleach-accelerators are to be synthetized, a thing that an amateur cannot do at home: "As pointed out above, the bleach-accelerating agents used in the present invention are known compounds. They can be easily synthesized by the skilled artisan.
The patent is this https://patentimages.storage.googleapis.com/70/83/d1/7bc4e4f5feb2a3/US4322493.pdf
Please note that in no case, never, Fuji uses a mixture of ferric nitrate and cerium as the bleaching agent.
The OP uses the wrong Fe compound.
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In a bleach where cerium is the accelerator, not the primary bleaching agent? Can you provide a reference for the quoted passage?
I've linked the paper.
Cerium IS NOT an accelerator and is not used as such.
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US4563405A - Processing solution having bleaching ability for light-sensitive silver halide color photographic material - Google Patents
Disclosed is a bleaching solution or bleach-fixing solution for a light-sensitive silver halide photographic material, which comprises an oxidizing agent comprising a diethylenetriaminepentaacetic acid iron (III) complex salt, and at least one metal ion selected from the group consisting of...
patents.google.com
Whether cerium would function similarly in the bleach presented in #1 is of course another question.
It doesn't apply since the paper you quoted is for color film. We are discussing b&w film here.
You can't simply extend the color bleaches composition into a b&w bleach, it won't work at all.
It depends whether the mechanism can be leveraged for a non-rehalogenating bleach.
Anyway, I'm off to do something more constructive.
It don't depends on anything. It simply won't work.
I stand here to discuss costructively with others.
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Color bleaches as generally used convert the developed silver back into a fixable form -- whether they're genuinely rehalogenating or not. Koraks was pointing out that these bleaches not working for B&W reversal depends on whether they can be made to simply dissolve away the developed silver without rendering the undeveloped halide impervious to fogging/development. The bleaches commonly used for color films today (EDTA/PDTA and ferricyanide) work by (partial) rehalogenation, so can't be used directly for B&W reversal, but I don't know any reason a ferricyanide bleach couldn't be made to convert silver to silver chloride (as it can be used for bleach/redevelop intensification), which then will preferentially fix in ammonium hydroxide solution.
This isn't a big improvement over copper sulfate bleach, which does the same thing and requires the same follow-up step, but suggests that categorically stating that no color bleach will ever be useful for B&W reversal is incorrect.
MattKing
Moderator
Thread edited above.
Comments on moderation are not permitted in these sorts of threads.
And on-topic differences of opinion with someone who just happens to be a moderator are just that - differences of opinion.
Keep it civil!
Comments on moderation are not permitted in these sorts of threads.
And on-topic differences of opinion with someone who just happens to be a moderator are just that - differences of opinion.
Keep it civil!
In this case, isn't the goal to get silver sulfate, not chloride/bromide?
that's it, color bleaches are not useful to a b&w reversal process because an ammonium hydroxide solution will damage the subbing layer (better yet: it will swell the gelatine so much that it will come off from the subbing layer) as much as a permanganate damages the subbing layer directly. An ammonium hydroxide at 25% W/W has a pH of 11.6 and a boiling point of some 37°C. So it's useless.
Please remember that it's not entirely the permanganate the culprit of the subbing layer failure (not so directly) but most of the damage comes from the big big pH swing between the alkaline first developer and the very acidic permanganic acid bleach.
The fact that dichromates doesn't impart such damage it's because dichromates tan the emulsion, counteracting its big swell.
In a color reversal process, all is calibrated to impart such pH swing that can be undertaken by a color emulsion, much much more hardened at factory stage than a b&w one.
Ammonium hydroxide outgasses very toxic fumes and will attack also the undeveloped remaining positive image, lowering DMax too much. You'll get a very weak positive that will be not usable in projection.
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Chemistry is not an opinion...
The preferred outcome is to somehow solubilize the silver, by whatever means, without damaging either the gelatin or the undeveloped halide. Existing methods of doing this are of limited utility because of the toxicity of the chemicals, softening/damage to emulsion layers, potentially damage to the undeveloped reversal image, and damage to the user. We keep looking for a better way.
Really?
I get excellent slides using the Adox reversal kit with Scala 50 film and Foma reversal kit with Fomapan 100 R: both without the slightest damage to the emulsion. Pure luck? I don't think so.
So there's a better way, using ready-made kits and tailor made films by a reputable manufacturer.
People are free to experiment and to share their findings, hypotheses etc. Also, the ready-made kits you refer to may not be available to everyone. In this case, the interest in non-standard bleaches is with our Chinese colleagues who have explained that access to chemistry is different for them. I wouldn't be surprised if the Adox or Foma kits aren't available to them in the first place.
So having established that the kits are an option if you're willing and able to use them, let's continue the exploration, theorizing etc. of alternative approaches. Your input that this may not be the best way is duly noted; now let's move on.
So having established that the kits are an option if you're willing and able to use them, let's continue the exploration, theorizing etc. of alternative approaches. Your input that this may not be the best way is duly noted; now let's move on.
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- relistan
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- Reason: Diversion
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