Hmmm, Gerald, is the THAT much stain? I've never used Pyro ...
For some reason, I suspect your answer to be too simplistic. It sounds reasonable, but for example, does the stain hold up to the bleach and fix properly and is the stain reasonable stable to the bleach and fix and storage after being near an oxidant.
There may also be image structure implications because you are leaving 'holes' where the silver used to be.
Have you ever done it?
I've heard of bleaching pyro negatives and printing the stain image -- done, among other things, to prove to skeptics that there really is imagewise stain, not just overall stain ("fog"). IIRC, they used Farmer's Reducer or something similar, a rehalogenating bleach and fixer rather than a direct solution bleach as usually used in B&W reversal.
Clarence, I'll post again on the B&W side when I get around to trying Tri-X in reversal. I'll probably start with shooting a roll with lots of bracketing, to ensure I have some exposures that are close to correct, give a "high contrast" development (which I'd take to be N+1 or N+2) with thiosulfate added, and then proceed with bleaching, fogging, and redevelopment. The Tri-X I have is 35 mm, but has been expired for quite a while, and predates the reformulation from moving the coating plant a few years ago. It's got a little bit of fog, but it's not noticeable with HC-110, only really shows in Caffenol.
The stain produced by Pyro or catechol is quit robust and is not a low MW dye but rather an insoluble product deposited in the emulsion related to humic acid. It consists of relatively high MW condensed phenols.
But, IIRC they are bleached by sulfite among other chemicals. Is my memory functioning properly here? If so, then in spite of being high in molecular weight and stable to oxidants, they may not be suitable in some cases. IDK.
The question remains. Has anyone out there tried it and are they willing to post some pre and post bleach examples? Can anyone comment from personal experience?
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High sulfite concentration prevents the formation of the stain but does not effect it once it is formed.
Bleaching out the silver from a pyro negative was a standard technique used many years ago to produce a grainless image.
Ok, is an additional comment.
Originally Posted by Gerald Koch
In all color products, holes are left where silver is bleached out. This can be seen in photomicrographs and in enlgargements and it is one of the 'goals' of the color system engineer to minimize those holes. The larger the grain of silver, the larger the voids formed when bleaching is done.
The tighter the dye particles around the silver grains, the more difficult it is to bleach the silver.
So, there are tradeoffs here. What you report may have been done years ago and the workers then may have thought the images were grainless, but were they? Has anyone done it recently?
I'm not disputing your comments BTW, I'm trying to add information to it based on my experience, and also trying to see if this has been done in modern times. Maybe the old work was done with LF negatives, and a modern repeat with t-grain films in 35mm might completely change this informaton. IDK, I have no idea.
I managed to try B&W reversal yesterday, and did another roll today. So far, so good; more information here:
Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.
Originally Posted by Photo Engineer
I have NOT tried this technique! It may NOT work!
But, then again, it just might!
I've wrestled with this issue -- how to develop a true silver negative, without the (silver) yellow filter layer, without degrading the negative image.
Good question. If anyone knows the answer, I'm all ears.
My first idea -- quickly discarded -- was to give a pre-bath in a B&W-reversal type bleach (permanganate or whatnot), to remove the CS yellow filter layer, without touching the undeveloped emulsion.
I quickly dismissed this idea when I realized that in addition to bleaching out the yellow layer, it would also eat away the latent image "seeds" in the undeveloped crystals, rendering the entire film "unexposed".
Oh well, would have been nice, but no cigar.
But then it hit me -- there is (I think ) a way to remove the yellow layer, and leave the actual negative content entirely unaffected!
What it would require is what I will call a "reversed-reversal" process.
First, develop the film normally (as a B&W film). This will give you a normal negative image, and, that accursed yellow filter layer will remain present.
Then, run the film through stop bath, and fixer, and then wash it. (In other words, up to this point, process it as if it were regular B&W film.)
Now comes the fun part: Turn the lights out (in other words, put the lid back on the tank).
Now bleach it with a rehalogenating (i.e., "color-type") bleach.
This will do two things. First, it will give you an "undeveloped" version of your negative (with the rest of the film "cleared" by the fixer), and, it will give you an "undevloped" version of the yellow filter layer.
Now the magic: Give the film a controlled re-exposure (you'll need to do a bit of trial-and-error to determine the correct amount of light to give it), and then, redevelop it.
This will once again give you two things: A developed silver negative, and, and UN-developed yellow filter layer! (You then run the film through stop bath and fixer, which removes the undeveloped yellow filter layer, then wash, and dry your negatives!)
How did that happen?
It's simple, when you think about it. The yellow filter layer is made from extremely tiny, microscopic silver grains. This means that even though they will be "light sensitive" when bleached, they will be much LESS sensitive than the actual negatives!
That's why a controlled re-exposure is so critical. You want to give enough light to re-expose the three emulsion layers, but NOT expose the much slower yellow filter layer. I would imagine that the amount of light necessary to cause the yellow layer to develop would be orders of magnitude greater than the amount necessary to expose the actual negative layers.
As I said, I haven't tried this, but I can't see why it wouldn't work. The key is that the yellow filter is made of silver grains that are many times less sensitive than the actual emulsion layers.
In a way, it's sort of like "doing a Kodachrome" on Kodachrome (or any color film using a colloidal silver yellow filter layer) -- selective re-exposure, to ensure that only the desired layers are developed.
Last edited by r-s; 11-03-2006 at 06:25 AM. Click to view previous post history.
The method I describe regarding reversal processing is mentioned elsewhere on APUG and has been tried. It works and gives reversal images.
The method described above by Ryuji will probably not work. The silver halide formed by the rehal bleach will form in a very fine crystal form determined by the form the developed silver is in, from tabular to filamentary. Therefore, it is a game of chance as to whether the silver haldies formed are sufficiently different in speed. The result would be a totally black piece of film with perhaps a very very faint image.