Old K-12 Kodachrome as negatives

What's the best method to use for bleaching out the silver filter layer in Kodachrome that's being developed for negatives? If I ever have the chance to do this again, I'll probably just get the last chemical I need and process them as B&W reversal slides; I can see there are images in this roll of found film (came loaded in my Motormatic when I got it a few months ago), but they're too heavily obscured by the filter layer to scan or print.

I've tried using Farmer's Reducer, both in proportional and subtractive forms, with little success; the problem is that the filter layer is almost as dense as the highlight areas of the image, and by the time it bleaches enough to be able to do anything with the images, the images have reduced to the point where I'm not sure I'll be able to retrieve them. I still have half the roll to try another method...

I've read on the Web that one needs to bleach away the blue layer and filter layer with a photographic bleach, but that page didn't say what -- I presume it must be fast-working to selectively take off those layers without simultaneously bleaching away the images in the red and green layers, since it has to bleach those layers before too much diffuses into the deeper layers of the film.

So, what can I use to bleach these Kodachrome negatives without completely removing the images? Potassium dichromate and sulfuric acid, i.e. regular B&W reversal bleach (and wear gloves up to my elbows)?

(Yeah, I know, maybe nothing will work -- they're not pictures of my grandma or anything, I can see they're just snapshots of someone's car and house, but found film is so much fun to look at!)

I suppose, worst case, I could cobble up a duplicating arrangement and rephotograph them with the sun behind the film; they're kind of low contrast this way, but that's controllable by increasing development of the copy film...

According to a friend, the instructions on this page worked for him

however, I do not personally know if they work.

http://lavender.fortunecity.com/lavender/569/k12bwnegdev.html

Hi Donald,

This may not solve your problem, but here goes.

I have successfully done K12 as B&W reversal (once) - old double 8mm film found in an old camera. I shot the other half and did some crude clip tests first, to establish that the film would darken in developer, clear in fixer, and to remove the remjet. I found that negative development removed all the dye except the colloidal silver layer which ended up being pale yellow, so I went for reversal (D-19 without added silver solvent, permanganate/sulphuric, metabisulphite, D-19 and hardening fixer). I do a lot of B&W movie reversal so I have the necessities at hand. The image was a bit thin (either due to old film, my technique, overexposure, or overdevelopment) still a viewable 2 minutes of old footage and 2 minutes of recent.

So far this doesn't help your present situation, but I have also been experimenting with removing the dye layers from old Kodacolor II 120 film and modern 35mm C-41 film. I have found that a bleach/redevelopment process works - with qualifications. In this method one bleaches in the presence of a rehalogenating agent to convert the silver image back to silver halide (or other developable compounds and then redevelops) The bleach removes the azo dyes but the image is maintained and can be reduced or enhanced (to a point) by adjusting the chemistry and times.

Here is the thread:

(there was a url link here which no longer exists)

Since PE's comment I have done more thinking and experimenting:

The azo dyes bleach out easily, but I am not sure if all the image layers of silver are being bleached/redeveloped non-selectively due to the chemicals diffusing to them more or less quickly. I don't have a densitometer, but I have found that fresh C-41 film exposed and developed in Rodinal and test printed through the orange mask (120sec. f/8) Agfa multi-contrast paper and Agfa multi-contrast developer followed by bleached/rehalogenated, redeveloped and re-printed gives a similar image. The dyes and CLS layer are removed. Well, I am not so sure about the colloidal silver layer - perhaps it is being retained as a grey layer after this process. This would add to b+f, evidence of which I don't see. My next test is to expose C-41 to test cards more or less matching the colour sensitivity of the three layers and see if the B&W redeveloped product selectively looses density in the various layers. This is to determine how close the redeveloped image density represents the original spectral range/sensitivity of the colour film.

Why do this? Well I regularly come across old C41 and C22 film and K-12 and earlier movie film, and would like to find the best way to print the previous and watch the latter.

Kodachrome is somewhat different, but somewhat the same. I don't think you will have any problem getting rid of the dyes, but you need to rehalogenate while bleaching to preserve the image. I have been using regular permanganate/sulphuric plus NaCl 10% w/v for bleach/rehalogenation mix (they must be together) in fact I have considered a NaCl pre-soak, but that may be unnecessary or harmful. I have done a fast and dirty dichromate enhancement with no success - probably my method - it works for others for regular B&W film and prints. There are many other soups - some of which you may have at hand.

Here are some other links:

Dead Link Removed
Dead Link Removed

I am going to be doing some Kodachrome this (long) weekend (it is the Queen's birthday - that would be Queen Victoria - in Canada - well actually it falls on May 24th, but has been made into a movable feast) and will report back how it worked. If you send me a PM with your mailing address, I would be glad to send you some samples of my results.

At present, I can’t recommend my method to someone with precious images, since it may not work in your case. I believe that it has good potential for these non-mainstream situations. Besides, it is fun to play.

If anyone has some ideas about this or is aware of some egregious lapse in my reasoning please comment.

PS I forgot to thank you for the info a while back about Exeter paper for backing paper. Got some but haven't tried it yet.

Cheers,
Clarence

Kodachrome has no dyes or dye couplers in the film prior to processing; the dyes and their couplers are presented during the three-step reversal exposure and color development process. Normal Kodachrome process, K-12 and K-14 alike, was (after removing the rem-jet) to develop all layers as a negative, then selectively expose and develop the red- and blue-sensitive layers from opposite sides of the film, with the silver filter layer preventing cross-exposure, then finally chemically fog and develop the green layer. Each step's developer introduces the correct dye couplers with the developer, depositing the dyes as development takes place; finally, the silver is all bleached away leaving only the three layer dye image.

B&W reversal will work because you bleach away the silver, then fog and redevelop.

Unfortunately, perhaps due to the age of this film, the silver filter layer has processed to a very high density (this is the same problem I had with the last Kodachrome II I tried, BTW, and it's of interest because I have two rolls of 1974-expired Kodachrome in 828 that I plan to shoot and would like to get usable images from). What I've read is that it's possible to bleach away the blue layer and filter layer, leaving the red and green layer silver images intact (at least sometimes).

I've gotten the sulfuric acid I need to try a dichromate/sulfate bleach on one of these strips, but I expect it to be quite tricky to bleach just enough. However, that gives me the last bit I need to do B&W reversal; a few practice rolls on nice, forgiving Tri-X and I'll be ready to try the Kodachrome.

Can anyone give a hint on what kind of reaction rate to expect with a halogen free dichromate bleach? Will I have a minute or two to react, or should I try dunking for a few seconds, then a wash and clearing bath to evaluate and repeat if needed?

Hi Donald,

Pardon my slip of the tongue about Kodachrome structure. However, I don't quite understand what you are planning to do with the 828. Are you going to develop as negative or reversal? Will you be bleaching the fixed negatives to remove the blue and silver filter layer?

Yesterday I shot the remaining frames on a relatively new roll of Kodachrome 35mm which had been in my Spotmatic II for about 8 months - essentially fresh - developed in Rodinal 1+25 for 7 minutes at 21C - incidentally - very high contrast, which had also slipped my mind. I shot duplicate pairs of frames so I could compare the original B&W developed images with the bleached and redeveloped images. I then bleached and redeveloped 10 frames. The silver filter layer cleared quite easily, but perhaps of more interest to your project, the top layers of emulsion slid off in the tank (ansco cheapo) during the redevelopment. I thought I had ruined the film, but one layer of the image is intact consistently (and is printable, though high contrast due to initial development) on each frame. I am somewhat puzzled by this. I don't have a scanner, or I would post the results. I have had the top layer of emulsion loosen at the edges of Kodacolor II by this same process on shots exposed many years ago, but not on recently exposed frames (on the same old roll of film).

At any rate, I have dichromate, acid, Kodachrome etc. on hand, and will try a test today on the regular dichromate/sulphuric bleach (no halogen) and see how fast the silver filter layer and image layers disappear.

Just to be clear, at what point in which process do you wish to test the dichromate bleach?

Also, I am not familiar with the emulsion structure of Tri-x, but I don't understand what you will find out by test bleaching it?

Also, as I recall, while the dyes etc. are added to Kodachrome during processing, the three silver halide layers represent different parts of the spectrum during initial exposure. By removing the blue layer you will loose that part of the B&W image. This may not be of concern, if it is a choice between an unusable image and a usable one with altered spectrum. I was concerned about this in my trials with Kodacolor II.

Cheers,
Clarence

Hi Donald,

I have some preliminary results as follows:

Bleach:
Potassium Dichromate 5g/l
Sulphuric Acid (conc.) 10ml/l

Clearing Bath:
Sodium sulphite 5%w/v

There is a range of dichromate bleach formulae in the literature, but I used the above because it is fairly strong (could be diluted if required) and I had the sulphuric on hand - already diluted to give the above final concentration. The dichromate is from JD Photochem and the sulphuric is sold in cubes to the automotive trade to fill batteries. I don’t know what impurities it may have, but it has worked well for b&w movie film reversal. I do about 25 rolls of Foma R 2x regular 8mm, 10 each of Super8 Tri-x and Plus-x and 1000ft of 16mm per year and haven’t had any problems – at least with the acid.

I cut some test strips from the Kodachrome 64 that I refer to in the previous post – some from the leader (totally exposed) and some from a length of film which was unexposed (no image – just the yellow silver filter layer)

The yellow layer cleared in 5 to 10 seconds leaving the frame numbers and the Kodak 5032 info at the film edge. These appear somewhat lighter than in the unbleached area, but the yellow tends to make the edge info appear darker. This can be demonstrated by viewing the cleared letters and numbers over a piece of un-cleared film. However, I have no doubt that some density has been lost.

The totally exposed strip took 60 seconds to clear. I was able to dip this strip in bleach by degrees to get an estimate of clearing/density loss vs. time.

Next I tried an image from the same roll for 8 seconds. It cleared perfectly, but there appears to be some image loss.

Since this process can be done by inspection (although the yellow dichromate makes it a bit difficult to see when the yellow silver filter layer is gone), I believe with some practice one would strike a useful balance.

Clearly, the time (less than 10 seconds) is too short to control easily and reproducibly. I tried a 1:5 dilution of the bleach and got times of about 30 seconds. Presoaking the film may slow it a bit (I didn't presoak).

Issues to address:

• When using the more dilute bleach it can be seen that bleaching progresses in a non-uniform way from the edges to the center (based on two trials). I don't know how long the bleaching action continues once the film is placed in the clearing bath (diffusion, etc.)
• There may be a better ratio of acid to dichromate at lower concentrations.
• One may have to bleach on a frame by frame basis to get the best balance of yellow layer removal and image loss.
• I have no idea, at this point, which of the layers of image is being bleached away and to what extent (although one can guess).
• The film I was using is relatively fresh, and although it was exposed pretty close to ASA 64, the b&w development I used was not ideal. A film with much less contrast would be easier to evaluate in the above trials.

In the next week I plan to do another fresh 35mm Kodachrome to further test this method and to shoot some old 8mm and 16mm Kodachrome which I have. Part of this I will develop as a negative to see how this bleach method works on old K12. I may have some K12 movie film left that was exposed when I got it, but I am not sure.

You mention above that, “…perhaps due to the age of this film, the silver filter layer has processed to a very high density (this is the same problem I had with the last Kodachrome II I tried…”

Do you mean that the layer has become a very dense yellow, or has the layer changed in some manner that makes it black? Could you speculate on what might have happened over time to cause this?

I noticed that the yellow filter layer in Kodacolor II film seemed to be denser in the areas that had been exposed approx. 30 years ago than in the areas of the frames that I shot just before processing.

If I can persuade a friend to scan the negatives I will post them.

Cheers,
Clarence

Guys, silver is silver whether developed by a developer or coated in the coating as the CLS yellow silver layer.

They have different sizes and shapes as particle, some being threads, some being tablets and some being colloids (CLS yellow silver).

Using a bleach to remove one type of silver will inevitiably remove all or part of another type of silver and therefore you will destroy image silver along with CLS silver no matter what you do.

So, the only way to get a clear Kodachrome B&W with no image loss, is through reversal B&W processing. You can approach it in a negative process, but only with image loss to some degree, usually severe.

If you are willing to process to a negative with a single color dye image, there are ways that you can make a single color negative developer, but it would probably be expensive and would require some preliminary trial and error. It is not impossible though.

PE

Photo Engineer said:

Guys, silver is silver whether developed by a developer or coated in the coating as the CLS yellow silver layer.

They have different sizes and shapes as particle, some being threads, some being tablets and some being colloids (CLS yellow silver).

Using a bleach to remove one type of silver will inevitiably remove all or part of another type of silver and therefore you will destroy image silver along with CLS silver no matter what you do.

So, the only way to get a clear Kodachrome B&W with no image loss, is through reversal B&W processing. You can approach it in a negative process, but only with image loss to some degree, usually severe.

If you are willing to process to a negative with a single color dye image, there are ways that you can make a single color negative developer, but it would probably be expensive and would require some preliminary trial and error. It is not impossible though.

PE

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Hi PE,

I agree. In fact I am amazed that one can bleach the CLS away and still get a usable negative at all. I don’t recommend it as a general practice. There are other ways, as you and others have pointed out, to get the image (paper spectral response, copy negatives, or horrors – scanning/computer manipulation). For newer Kodachrome, b&w reversal (assuming one doesn’t want the regular K-14 process) is the best route. However, for older film it might just be better to develop as negative and work from there. Once you go for reversal, there is no turning back. Fog becomes density loss, etc. With negatives one has a number of options to clean up the image. I expect that is why Rocky Mountain Film Lab does K-11 and K-12 by negative plus scan. The trials I am playing with (and I mean playing) are a response to a question by Kino, Donald’s present inquiry and some problematic film for which I had with no alternate resources in my remote location. I don’t expect much from it, but as I said, it is surprising to get a printable result at all.

Thank you for providing clarity to the various forms of silver metal in these films.

I am interested in the monochrome developer you refer to. Could you elaborate, or at least point in the right general direction? Would the single color dye image combine all the information in the separate layers, or would it be a method of developing just one of the layers to the exclusion of the others and of course the CLS?

Cheers,
Clarence

Okay, to clarify: what I intend for the 828 Kodachrome I still have, now that I've gotten some sulfuric acid to make reversal bleach, is to develop as B&W positives -- which ought to be no problem, beyond the film being 30+ years old. Little lost if it doesn't work, I'll still get the spools to use in respooling cut-down 120 for use in the Bantam RF camera. However, I'll surely try B&W reversal a few times with film I know is okay before attempting it with the 1974-expired 828 Kodachrome (too many variables -- first dev time, how much thiosulfate to put into the first dev, what dev formula to use, etc.; the more I can work out on Fomapan 100 or Tri-X, the better chance I have of getting usable images from these old 828 rolls.

Meantime, I've still got half the roll of 35 mm Kodachrome II that processed with a heavy layer of what looks like fog. This is *not* a yellow filter layer; it looks like the negatives are badly fogged (and they might well be; I don't know how old the roll was, with no date on the cassette, or what storage conditions it was subjected to while sitting for, I'd guess, at least 30 and possibly 40+ years in that Motormatic before I received the camera). Subtractive Farmer's Reducer, however, which I'd expect to help a fogged negative, reduce the image too much to scan readily by the time it had reduced the fog enough to be within my scanner's density range.

I guess that shouldn't surprise me; there's just not that much difference between the fog and the image, so there won't be much contrast no matter what I do. Parodinal probably wasn't the best choice of developer, either; the K-12 B&W process I've seen suggests a high-contrast developer like D-19, and the anti-fog ability of my current Parodinal variant isn't well tested.

Whether it's the colloidal silver layer or plain fog, what I have on this film is a very dark, almost black appearance over the entire film area (sprocket holes and all). I've read some things that suggest the colloidal silver layer can change to black in processing, but I don't have any way to check if that's what's at work here or if this is just plain old fog.

I'll try a strip of these negatives in dichromate/sulfuric bleach, applied incrementally at high strength (seems the best chance of leaving the layers below the silver layer, if it's not just fog in all the imaging layers), and report back what I got, but at this point, I expect very little.

I wonder, on that monochrome dye negative developer -- could something like this be improvised from bleach/redevelop dye toners made for prints? I've seen those sold at reasonable prices, even in multi-color kits. Presumably you'd apply the color developer, bleach with a rehalogenating bleach like ferricyanide or C-41 bleach, and then fix normally, or obtain a monochrome negative (from pretty much any silver-based film, come to that).

Hi Donald,

Ok. Now I think I understand. I use D-19 for all my b&w reversal processing - used the Kodak t-max reversal some years ago, but it was pricey. D-19 is actually relatively cheap in Canada - $5.19 CDN (powder to make 128oz.) plus flat rate shipping from Henry's - a big issue with me so I buy 20 at a time. I don’t think they ship chemicals to the US - although it is no big deal to make your own. Many reversal procedures call for a high contrast first developer. I know very little about K-12 as b&w (except for a few trials) but the K-14 I developed as a negative in Rodinal looked like Tech Pan. I prefer re-exposure to a fogging redeveloper. For movie film I usually second develop to completion, so there is not really a lot of tweaking after the first steps. I don't know if you have done reversal before, but it is a lot of fun and potentially addictive.

I usually use permanganate bleach, partly because I had it at hand first. I use potassium dichromate for gum printing (more recent habit). It is probably preferable for reversal than permanganate although somewhat more toxic.

I am still musing about the monochrome dye negative developer - could be interesting.

Cheers,
Clarence

For those interested in a monochrome developer for Kodachrome to give a negative dye image, here is the basic formula and the basic problem involved:

1. Use a normal C41 developer, but add a Kodachrome type coupler such as a cyan, magenta or yellow. (I can post these later if you wish, as I don't keep them in my head).

2. Develop in this C41 developer to get a monochrome image of whatever color you have designed for in 1 above.

3. Bleach, fix, wash and stabilze as normal.

4. The process must be at 68 - 75 deg F as older films and B&W films (yes this will work for B&W as well as Kodachrome) cannot stand higher temps. You will have to do some tests beforehand to determine development time, but my tests indicate that it will be on the order of 15' - 30' at 70 deg.

Problems:

1. The final image will only be as stable as the dye formed. Since we will never be able to readily get the real Kodachrome couplers, the ones we would use would be bottom of the line stuff. Not very good for much of anything but fundamental imaging.

2. The chemicals (couplers) are going to be expensive.

PE

Hi PE,

Thank you for the info. I would appreciate your info concerning Kodachrome-type couplers when you have it conveniently at hand. Even if it is too expensive/impractical/etc. I would like to consider trying it.

Cheers,
Clarence

According to Leadly and Stegmeyer, the use of 2, 4 dichloro-1-napthol at 1 g/l added in an acetone solution (I would use either methyl or isopropyl alcohol myself) will give a cyan image.

This is better than using the actual Kodachrome coupler and developer which is complex and expensive, and it is a good starting point.

PE

I like that idea, PE; where can you get said coupler??

Also, there are chromogenic toning kits (Rockland has one for $50 - ish), so those would probably be another option.

IDK where to get the coupler. The toning kits are based on existing silver images IIRC.

PE

CRhymer said:

I use D-19 for all my b&w reversal processing - used the Kodak t-max reversal some years ago, but it was pricey. D-19 is actually relatively cheap in Canada - $5.19 CDN (powder to make 128oz.) plus flat rate shipping from Henry's - a big issue with me so I buy 20 at a time. I don’t think they ship chemicals to the US - although it is no big deal to make your own.

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I have everything I need to make D-19 unless it's got something odd in it. Lemme look -- yep, metol, hydroguinone, sodium carbonate, sodium sulfite, and potassium bromide. Twenty minutes, starting from checking that the wife won't need the bathroom, er, darkroom. I've even got sodium hydroxide on hand to make the replenisher, if desired.

Many reversal procedures call for a high contrast first developer. I know very little about K-12 as b&w (except for a few trials) but the K-14 I developed as a negative in Rodinal looked like Tech Pan. I prefer re-exposure to a fogging redeveloper. For movie film I usually second develop to completion, so there is not really a lot of tweaking after the first steps. I don't know if you have done reversal before, but it is a lot of fun and potentially addictive.

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This is the way I've always read it should be done -- all steps after first dev carried to completion; any contrast controls are done in the first dev. I've also read on several occasions that some thiosulfate (got a few pounds) added to the first dev helps clear the highlights by removing the extra-fine halide grains that never develop and are usually fixed away, even in the hottest highlights.

I usually use permanganate bleach, partly because I had it at hand first. I use potassium dichromate for gum printing (more recent habit). It is probably preferable for reversal than permanganate although somewhat more toxic.

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The biggest issue with dichromate (which I also bought mainly for gum and similar processes, but then neglected to buy any gum arabic -- possible substitute in hand, just need to test) is that, many places, it's literally a crime to put it down the drain, because of environmental concerns with the hexavalent chromium (and never mind that it doesn't and can't stay hexavalent long in an environment like sewage, rich in weak reducing agents that will tend to quickly take up the oxidation potential of the chromium). And of course there are "national security" issues with both because they're oxidizers -- but I have dichromate and I don't have permanganate, so dichromate bleach it'll be (though I might yet get a can of tree root killer from the hardware store and try copper sulfate as a bleach -- I've heard it reviled, but don't think I've heard of anyone using the formulae I've seen that effectively mimic permanganate or dichromate reversal bleaches. And it's cheap, typically around US$7 per pound.

I am still musing about the monochrome dye negative developer - could be interesting.

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Ron has corrected my confusion on that -- the dye toner kits are fogging redevelopers, not latent image developers like C-41 color dev. They'd be usable to obtain a dye positive from Kodachrome, however; suitable first dev, color toner dev, rehalogenating bleach (C-41 bleach would be least likely to damage the dye image) and fixer. Simpler process (slightly) than B&W reversal, but still issues with permanence of the dyes; they're intended for prints for special purposes, not for archival longevity. Probably not worth the effort.

I'll probably try B&W reversal on Tri-X (mostly because I have a lot of it still around) in the next week or two, now that I have a cube of battery acid on hand. Four bucks for a quart of 33.5% sulfuric, I figure that's a multi-year supply... And while there's no telling what impurities are in there, it's been reported by many others to work fine in reversal bleaches.

Hi Donald,

I'm sure you will do fine with dichromate. Copper sulphate may work, but we know that dichromate will work well. In fact, now that I have some mixed up for testing, I will probably switch for my movie film reversal (I use a saturated solution for stock in gum printing). Yes, other gums will work, or you could do egg tempera. I have used a number of gum arabic sources, but have recently changed to Daniel Smith's "pit run" variety - works well and has preservative - thanks to the advice of Judy Seigel (alt-photo-process list and World Journal of Post Factory Photography - kind of off the wall, but useful and entertaining). I had to wait until past the threat of frost before getting it shipped to the North. Permanganate is stable until it is mixed with acid, then must be used promptly and discarded. Dichromate can be premixed and reused. I agree about disposal, but you can always just add some sulphite to it before you dump it. The biggest risk with dichromate is weighing and mixing the powder - a face mask, old newspaper under the works, and rubber or nitrile gloves are a good idea. Discard the newspaper and mask after mixing. Of course, at least the dichromate can be easily seen due to the bright colour - true for permanganate as well.

The T-max reversal kits had some info about adjusting the second developer time, but I have never bothered. I don't usually use a halide solvent, but have sometimes regretted it. Thiocyanate probably works a bit better and is not a problem at the low levels used, but hypo (which you have) works fine as well. As I recall, it is best to add it just before you start development. If you re-expose there is the possibility of printing out by overdoing it, which I think I actually did once, but there is a lot of latitude, so it is not likely to be too big a concern.

One thing that I have never addressed adequately is the adjustment in exposure to negative films for reversal processing. Kodak has recommendations for Tech. Pan and T-max 100 for their reversal kit, but I am not sure what speed to shoot Tri-x at to achieve sufficient gamma – it may depend on which Tri-x you have. The dr5 site has some info at: http://www.dr5.com/filmprintout.html for their process.

I have used a number of 16mm movie negative emulsions for reversal, and found that they usually worked better when shot at half their rated speed (increased exposure). Some were out dated, but not ancient.

There are also many suggested development times for the first developer. I have found that 8 minutes @ 20 degrees C. for D-19 (with pre-soak) is a good starting point for movie film.

I would be interested in your experience with Tri-x.

Cheers,
Clarence

posted by PE:

The toning kits are based on existing silver images IIRC.

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The rockland one is actually couplers and a p-phenylene diamine based developer.

htmlguru4242 said:

posted by PE:



The rockland one is actually couplers and a p-phenylene diamine based developer.

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You are correct.

I was referring to true toning in color which relies on pre-formed silver images. Sorry for the error in my post.

You have to start with an undeveloped film for the rockland toners to work, and they would work fine with Kodachrome. AAMOF, one could develop Kodachrome given CMY toners. Although I would call them color developers.

You can also bleach an already formed silver image back to a silver halide with a rehal bleach and then 'tone' in the rockland 'developers'.

PE

To get a printable negative image just use a staining developer based in pyro or catechol and after development bleach out all the silver. No need to buy a coupler and any other exotic chemicals.

Hmmm, Gerald, is the THAT much stain? I've never used Pyro ...

Gerald;

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?

PE

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.

Gerald;

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?

PE