Quick question on bleaching film

nickandre · Apr 14, 2008

After a silver image is bleached back to halide (in the dark), would this be exposed or unexposed halide?

Also, is there any way to un-fog film?

fschifano · Apr 14, 2008

Good question, and I don't know for sure. I'm leaning towards the halide being develop-able though. Try it with some paper. Bleach it back, then redevelop it under safelight conditions. See what happens.

snallan · Apr 15, 2008

Bleaching in the dark, with a rehalogenising bleach, will give you unexposed halide.

Are you considering bleaching film to tackle general fog? If so, I would think it is going to be a very hit-and-miss affair. I would imagine a very brief dip (of well soaked negatives) in a subtractive reducer, and quickly washing would start removing the fog silver. But. There would be no easy way to control this, and you are likely to lose any delicate highlights during the process. That is not to say it can't be done, after all we do it with prints, but with a print it is much easier to judge the extent of bleaching. If you already have the processed negatives, it would be better to work around the fog at the printing stage than risk damaging the image.

If you have old film to develop, and you know it is going to have a high general fog, it is better to develop to minimise fog in the first place, rather to try and handle it later.

nickandre · Apr 15, 2008

I was simply thinking about 120 kodachrome, and if someone processed it as a B+W reversal if it would be possible to later process it as a color slide by bleaching and then following the kodachrome selective re-exposure development...

The second part of my question is assuming I have a lovely roll of film that I just fogged or has some base fog from the years, and say it was kodachrome 25 or something worth it/valuable, would it be possible to un-fog this film and then expose and process it?

This is theoretical...I don't have a use for it, yet.

Ryuji · Apr 16, 2008

Bleached silver halide doesn't work like the original emulsion. The crystal size, shape, composition, etc. are all very different.

dancqu · Apr 16, 2008

tiberiustibz said:
(in the dark)

In the dark? I'd think a yellow or orange
safelight would do. Dan

nickandre · Apr 16, 2008

dancqu said:
In the dark? I'd think a yellow or orange
safelight would do. Dan

For panchromatic film?

nickandre · Apr 16, 2008

Ryuji said:
Bleached silver halide doesn't work like the original emulsion. The crystal size, shape, composition, etc. are all very different.

What would the result of this be? Would the shadow detail be lost or would it become grainier or fuzzy or something like that?

gainer · Apr 16, 2008

What made it panchromatic was not the form of the silver halide, but some dyes that were removed in the original processing. What you have left in the case of B&W film is the silver image. It is not very sensitive to light. The final image in color film is purely dye and cannot be bleached and redeveloped. Transparencies are developed first in a monochrome developer to get B&W negatives in the several color layers. These are either exposed to very strong light (old way) and developed in a color coupling solution, or developed in a fogging color coupling solution. In either case, the silver is bleached out, leaving only the dye image. This dye image can be bleached, but if so it is lost for good. If you have ever spilled chlorine bleach on clothing, you know what happens.

Ryuji · Apr 16, 2008

tiberiustibz said:
What would the result of this be? Would the shadow detail be lost or would it become grainier or fuzzy or something like that?

Worse than that.

Most film emulsions contain silver iodobromide crystals of multiple layers, and they are chemically sensitized.

By developing the crystals, you are converting them all to metallic silver, losing the internal and external structure, chemical composition, etc. Just plain silver. Not even crystal. The developed silver takes the shape of steel wool, made from silver filament.

By apply rehalogenating bleach, you are converting back the silver steel wool to silver bromide. It's not even an orderly crystalline structure. It has no multi-layer structure. It has no chemical sensitization. It has no sensitizing dye.

To put it another way, I know how to make silver halide photographic emulsion from raw chemicals, but I have never heard of making useful film emulsion by bleaching particles of metallic silver.

It's just that much different.

el wacho · Apr 16, 2008

Hologram · Apr 17, 2008

Ryuji said:
Worse than that.

Most film emulsions contain silver iodobromide crystals of multiple layers, and they are chemically sensitized.

By developing the crystals, you are converting them all to metallic silver, losing the internal and external structure, chemical composition, etc. Just plain silver. Not even crystal. The developed silver takes the shape of steel wool, made from silver filament.

By apply rehalogenating bleach, you are converting back the silver steel wool to silver bromide. It's not even an orderly crystalline structure. It has no multi-layer structure. It has no chemical sensitization. It has no sensitizing dye.

To put it another way, I know how to make silver halide photographic emulsion from raw chemicals, but I have never heard of making useful film emulsion by bleaching particles of metallic silver.

It's just that much different.

I agree that this seems to be the case for most photographic emulsions. However regarding very fine grained materials, Lippmann/holographic emulsions, it's not entirely so. Principally, these materials are spectrally sensitized black and white emulsions with grain sizes of say, 5-50nm.

In an almost forgotten 1929 paper (www.holographyforum.org/lippmann/Le...metrie_de_plaques_photographiques_a_grain.pdf) Leroy showed the making of a Lippmann emulsion by bleaching a colloidal silver layer. He basically mixed gelatin with colloidal silver particles and used this solution to coat glass plates. Those layers were then bleached in a diluted rehalogenating copper sulfate bleach. The paper explicitly mentions the possibility of spectral sensitization.

Also, still referring to very small grained emulsions, you can expose, develop and rehalogenate a Lippmann/holographic emulsion to expose it to actinic light for a second time. In other words, you record an image which then is erased (bleached) to make a second recording on the same layer.
By the way, speed may be surprisingly high. And depending on the bleach formula, the spectral dyes may remain intact. This is certainly the case for ferric EDTA and copper sulfate bleaches.

There's a serious issue though: bleaches tend to introduce scatter. This may relate in part to the newly formed AgX grains being actually mixed crystals, AgX + part of the bleaching agent (iron, copper etc.). I guess that kind of scatter is likely to grow exponentially with larger grains.

dancqu · Apr 17, 2008

Hologram said:
However regarding very fine grained materials,
Lippmann/holographic emulsions, ...

Grain size: microfilm vs B&W print paper vs Lippmann.
I'm interested because grain size is sometimes associated
with image tone and a toner's or image's preservation
characteristics. Dan

nickandre · Apr 17, 2008

so the answer to re-processing kodachrome in color is no if the sensitizing dyes are lost because the selective re-exposure would not work because the different exposure is gone, but yes with some possibility if the bleach retains the sensitizing stuff.

I just realized this wouldn't work at all because the yellow filter would be gone. Oh well, :-(

gainer · Apr 17, 2008

Reprocessing Kodachrome in color? If the initial processing was done so that you can see the colors, there is no silver left to rehalogenate. Bleaching the color just removes the color. If you want to change the color balance of a Kodachrome, you'd best do it with monochrome copy negatives made through color separation filters and printed by dye transfer.

Ryuji · Apr 18, 2008

I've not studied emulsions for holography, but grains smaller than 50nm is difficult to handle by conventional emulsion making techniques. That's probably why bleach technique was attempted, and if that actually works for emulsion of that size, great. I remain very skeptical of its advantage over more conventional technique, when available, though.

I've not attempted to make emulsions of that type, but if I were to do it now, I would probably blend fish skin gelatin, poly(vinyl alcohol), poly(vinyl pyrrolidone) as the peptizer and precipitate at the lowest possible temperature... and if that doesn't get the grain small enough, i'd start trying some restrainer like adenin.

Hologram · Apr 19, 2008

Ryuji said:
I've not studied emulsions for holography, but grains smaller than 50nm is difficult to handle by conventional emulsion making techniques. That's probably why bleach technique was attempted, and if that actually works for emulsion of that size, great. I remain very skeptical of its advantage over more conventional technique, when available, though.

Yes, I've to admit the results from the bleach technique I've seen so far are not really convincing.

Ryuji said:
I've not attempted to make emulsions of that type, but if I were to do it now, I would probably blend fish skin gelatin, poly(vinyl alcohol), poly(vinyl pyrrolidone) as the peptizer and precipitate at the lowest possible temperature... and if that doesn't get the grain small enough, i'd start trying some restrainer like adenin.

I never tried adenin (Glafkidès mentions this agent among xanthine, guanine. He points out its addition resulted in a loss in photographic speed).
But I tried PVOH and PVP. PVOH isn't very compatible with gelatin. And using PVOH only, it becomes difficult to do desalting. Moreover, I got high fog levels with PVOH emulsions.
PVP looks more interesting though it may tend to reduce silver nitrate.

nickandre · Apr 28, 2008

gainer said:
Reprocessing Kodachrome in color? If the initial processing was done so that you can see the colors, there is no silver left to rehalogenate. Bleaching the color just removes the color. If you want to change the color balance of a Kodachrome, you'd best do it with monochrome copy negatives made through color separation filters and printed by dye transfer.

I know. I was wondering if someone were to process 120 kodachrome in b+w reversal if it would be possible to re-process in color. This wouldn't work.

Quick question on bleaching film

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