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B/W reversal Bleach Bypass


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There IS no bleach step in processing b&w film anyway so in effect you are always "bypassing" it.

 

Do you know what the bleach step does in the first place? When you expose color film, the silver halides grains that receive light become "developable" -- i.e. hold a latent image. When color film is developed, an equal amount of color dye is formed along with the metallic silver. To then remove the silver, the bleach step reconverts it to silver halide, as if it were never exposed (all the unexposed areas of the frame remain silver halide.) The fixer and wash steps then removes all the unexposed silver halide, leaving only color dye. So skipping the bleach steps leaves the metallic silver unconverted to silver halide and therefore it never gets removed by the fixer and wash steps.

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Regular process for b/W reversal is.

Developer-Bleach-rexposure-developer-fix

The bleach bath involves sulfuric acid.

I wonder if taking the bleach out will give similar results in contrast like when you do it in a color process.

Maybe not doing the bleach will cause bad rexposure.

Did anyone try before?

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You can do it and essentially turn your B&W reversal stock into a negative stock, but it will be very contrasty since the stock was designed with projection contrast gamma, not neg. contrast. It won't be particularly grainy, although in trying to get a print through that high con neg. you'll probably introduce a lot of grain.

 

I did this once as an experiment years ago. The results were not particularly useful.

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I know what a cross process is but i´m not interested about since i want a positive image.

I´d like to know the result from doing:

dev+rexposure+dev+fix

that´s skipping the bleach but staying in a reversal method.

maybe it works, but i´d like to know if anyone tried before

thanks

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I believe the bleach is essential in reversing the image into a positive one, by allowing the initial density created by exposure to be removed, leaving the reverse levels of density of silver halide, which is then exposed and redeveloped. So if you skip the bleach step, you never remove the first layer of silver so you end up with a negative image.

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Paraphrasing the Filmmakers Handbook:

 

About reversal processing:

 

The developer converts the exposed silver halide of the latent image into metallic silver.

 

Whereas in negative processing, at this point the unexposed silver halide would be removed by the hypo (fixer) and wash, instead with reversal processing, the metallic silver is removed instead by immersing the film in a bleach, leaving the unexposed silver halides, which are still light sensitive, in the emulsion.

 

The silver halides are exposed to light and then redeveloped again, and fixed in the hypo.

 

So if you skip the bleach step, you will not end up with a "reversed" image -- i.e. it will stay a negative image.

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Eliminating the bleach step in a B&W reversal process will leave ALL the silver in the film, in other words, no image --- the film will come out of the process BLACK. :wacko:

 

Here is the process sequence:

 

http://www.kodak.com/US/plugins/acrobat/en...h2415/h2415.pdf

 

http://www.kodak.com/US/plugins/acrobat/en...ssing/H-661.pdf

 

If you are not familiar with safe chemical handling, weighing, and mixing, better and safer to buy the prepackaged chemicals. And read and follow all the safety instructions.

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