Permanganate reversal baths

Jordan · Sep 28, 2004

Hi David, I would also be interested in knowing specifically what differences in image quality you see for permanganate vs. dichromate bleaches, since yours is the first mention I have read of a final image quality difference between these two bleaches. Is it grain or tonality or something else?

Oxidizers like permanganate and dichromate are usually toxic but some are more toxic than others. Rather than a quack remedy, permanganate seems to be pretty commonly used in dilute solutions as a treatment for athlete's foot and other related skin infections. Wouldn't want to do that with chromium salts... Cr(VI) is certainly fine to use when handled correctly -- OTOH I agree with you David that many people are not likely to handle it correctly.

Ed Sukach · Sep 28, 2004

This doesn't seem to be the first time I've heard of potassium permanganate used for medicinal purposes - as an antiseptic (??).
Any "Medical Types" out there who can confirm or reject?

P. S. Potassium Ferricyanide - I've heard various comments about its "harmfulness" . The bottle I have does not carry a "Poison" label... the only chemical in my darkroom that does is Kodak Indicating Stop Bath (acetic acid), and I'm serously thinking of going to diluted white vinegar when I run out.

Helen B · Sep 28, 2004

David,

I mentioned permanganate baths as an aside - I have good memories of what appears to be a weird application to people who are unfamiliar with it. I didn't expect to be called 'nuts' or to be told that it blew my credibility. As you perceive it to be such a contentious issue, and still persist in using it to question my sanity, I'll go off topic for a while.

I have read the MSDS for permanganate. What made you think that I hadn't? Don't I come across as someone who does her homework? The MSDS refers to the dangers of comparatively high concentrations of permanganate. Typical therapeutic baths are 1 to 10 000. Manganese is not accumulated in the body. Fish can survive swimming in dilute permanganate though they mustn't be in it long enough for the manganese level in their blood to rise to heart-stopping levels - it's used in vetinary medicine as well.

There is plenty of evidence that shows that the worst effect of bathing in dilute permanganate is a fake tan - hey, you might be mistaken for a Californian. In cases of acute infection with inflammation of your entire skin (ie your whole body is covered in oozing sores) permanganate baths are a rapid and effective route to normality. Or near-normality in my case.

Back to the subject at hand.
'I know its the best development for B&W available.'
When I get home tonight I'll post a comparison between some TXP you processed and some I processed.

I didn't find your comment insulting, and I didn't say that I was insulted. Your comment said more about you than it did about me. I just thought that personal remarks were out of place in a discussion like this, so I suggested that you avoided them. It's no big deal.

Best,
Helen

Later edit, in reply to Ed's question:

Quick quotes from

Principles of Pediatric Dermatology:

Potassium permanganate compresses
These are used in different concentrations. Potassium permanganate compresses in concentration of 1:9000 are used by clean gauze moisten with the solution and applied repeatedly to the skin lesion for 10 minutes every four hours. When the gauze is dry it should be moistened again and repeated application each time is necessary.
The brown staining of the skin can be removed with lemon juice.

Wet dressings
Wet dressing is used as a soothing and cooling antiseptic on dry inflamed skin lesions as in oozing eczema.
Potassium permanganate is an effective and widely used dressing. Potassium permanganate five grains added to 3 qt make a solution of 1: 9000 concentration is an optimum wet dressing to dry oozing lesions as in acute dermatitis.

and the Oxford Handbook of Sports Medicine, in reference to athletes foot: Soaks should be lukewarm and contain potassium permanganate 1 in 10 000 and the feet immersed in the solution for 15 minutes three times daily.

Plenty more if you want...

Im not sure whether I bathed in 1 : 10 000 or 1: 9 000. The nurses just told me to put enough in to give a purple colour, and stay in for half an hour. I was in a hospital in S E Asia for people with communicable diseases, and the nurses definitely didnt want whatever it was that I had, so they pretty much left me to it. Remarkable how quickly you can learn to do an intravenous drip when its you that needs it.

Helen B · Sep 28, 2004

One of my recent posts has gone missing - lost during problems with the server? Here it is again, more or less.

Some information from Agfa that sheds some light on the issue:

When processing black-&-white reversal films and in micrographics and the graphics sector, the developed silver is bleached with bleaching baths which contain a strongly acidic potassium dichromate solution containing approximately 7.5 g of K.sub.2 Cr.sub.2 O.sub.7 /l as the oxidising agent. A soluble silver salt, for example silver sulphate (Ag.sub.2 SO.sub.4), is formed during the bleaching operation, and is rapidly washed out of the photographic layer.

It has become important on environmental grounds to reduce the quantity of dichromate or, preferably, entirely to avoid bleaching baths containing dichromate.

Substances having a similarly high electrochemical oxidation potential as dichromate, such as for example salts of tetravalent cerium, heptavalent manganese, trivalent iron and persulphate solutions are not suitable because, even at elevated concentration, they oxidise metallic silver only slowly (bleaching times of more than 10 minutes) or because, as in the case of heptavalent manganese, while they are indeed sufficiently active, they are so unstable in solution that they decompose after a short time and deposit manganese dioxide on the tank walls, in the hoses, on all equipment components and on the belts.

Combining the stated oxidising agents with known bleaching accelerators, for example thioglycerol, is also unsuccessful because bleaching times still remain above 10 minutes. Moreover, this method requires an additional bath (prebath) because sulphur compounds such as thioglycerol are immediately oxidised by the oxidising agent in a combined bath and thus rendered ineffective.

The object of the invention was accordingly to provide a bleaching bath for black-&-white silver halide materials which allows bleaching in a reasonable time (<10 minutes), is stable, may be used in continuous regeneration operation and contains at most 3.4 mmol of dichromate/l. The bleaching bath should preferably contain no dichromate.

This object is surprisingly achieved by the combination of at least 2 oxidising agents having an oxidising potential of .gtoreq.500 mV, optionally together with a metal salt having a stabilising action of a metal of subgroups 1 or 2 of the periodic system of elements, wherein, in the event that dichromate is used as one of the oxidising agents, it is used in a quantity of at most 3.4 mmol/l.

Suitable oxidising agents are, for example, persulphates and metal salts in elevated valence states.

Suitable persulphates are, for example Na.sub.2 S.sub.2 O.sub.8, K.sub.2 S.sub.2 O.sub.8 and (NH.sub.4).sub.2 S.sub.2 O.sub.8.

Metal salts having an elevated valence state are, for example, salts of tetravalent cerium, heptavalent manganese and trivalent iron.

Metal salts of subgroups 1 and 2 are, for example, AgNO.sub.3, CuSO.sub.4, ZnSO.sub.4 and CdSO.sub.4. Surprisingly, these metal salts stabilise permanganate solutions, for example, so suppressing the formation of manganese dioxide.

The persulphates are in particular used in a quantity of 0.001 to 0.5 mol/l, preferably of 0.01 to 0.1 mol/l.

The metal salts having an elevated valence state are in particular used in a quantity of 0.001 to 0.2 mol/l, preferably of 0.01 to 0.1 mol/l, wherein, as stated, the quantity of dichromate does not exceed 3.4 mmol/l.

The metal salts of subgroups 1 and 2 are in particular used in a quantity of 10.sup.-1 to 10.sup.-4 mol/l, preferably of 5.multidot.10.sup.-2 to 5.multidot.10.sup.-4 mol/l.

The bleaching bath according to the invention in particular has a pH value of 0 to 2, preferably of 0.1 to 1.5.

In order to shorten the bleaching time, an upstream bath with a bleaching accelerator, for example thioglycerol or 3-mercapto-1,2,4-triazole, may be used. This bath preferably contains the compound containing sulphur in a quantity of 10.sup.-4 to 10.sup.-1 mol/l.

etc

It's from US patent nr 5,716,767 and the full text can be found by searching on the patent number at http://www.uspto.gov/patft/index.html

You might also like to do some searches like

(an/agfa-gevaert or an/agfa) and ((abst/black and abst/white) or abst/reversal)

which means applied for by Agfa or Agfa-Gevaert and containing 'black' and 'white' or 'reversal' in the abstract. I think.

Anyway, reading that got me thinking - why was I not having problems? I'm guessing that the answer is down to using inversion processing in small tanks and using fresh solutions for the bleach and the clearing baths. Less carry-over. Constant, brisk agitation.

Best,
Helen

Later edit: If you look at the full text of the patent, or better, the image of the patent, you will see the results of tests that Agfa carried out with various formulae on developed APX100. The formula, time and final density are given.

Patent 6,350,563 also gives quite complete details of a process (need not be the process) for 'A commercially available black-and-white reversal film, e.g. that of film speed 200 supplied by Agfa-Gevaert AG'. While one wouldn't want to copy these, there is useful background information.

Jorge · Sep 28, 2004

or because, as in the case of heptavalent manganese, while they are indeed sufficiently active, they are so unstable in solution that they decompose after a short time and deposit manganese dioxide on the tank walls, in the hoses, on all equipment components and on the belts.

Anyway, reading that got me thinking - why was I not having problems?

I think there is your answer, apparently if you use permanganate with fresh solution as a one shot deal you can use it. I am sure this would not be desirable for commercial operations but seems to work for us lab rats.

OTOH on the book I was telling you (Developing) they use permanganate solutions as bleach, so it might not be as unstable as Agfa seems to think.

Jorge · Sep 29, 2004

Real correct info about permanganate...

If anybody really wants to read about the laws in the US and permanganate, go to the US EPA site and read the CFR 40(Code of federal regulations title 40) I have included a link as an example:

Dead Link Removed

Jordan · Sep 29, 2004

Later edit: If you look at the full text of the patent, or better, the image of the patent, you will see the results of tests that Agfa carried out with various formulae on developed APX100. The formula, time and final density are given.

Patent 6,350,563 also gives quite complete details of a process (need not be the process) for 'A commercially available black-and-white reversal film, e.g. that of film speed 200 supplied by Agfa-Gevaert AG'. While one wouldn't want to copy these, there is useful background information.

Helen, this is really interesting information.

A word or two on viewing patents from the USPTO on-line. Normally you can view patents either in plain-text (with no images and hard-to-read chemical information) or through the AlternaTIFF plug-in (with images, but you can only save and print one page at a time). I stumbled across a free web-site this afternoon that automates the process: give it a patent number and it puts the patent in its original format into a PDF file, using an open source script. It's called pat2pdf and it works well. I've just used in on Helen's two patent numbers.

Anyway, this info is really useful. I had long suspected that there was a way of making the bleaching process catalytic in metal salts (using some kind of persulfate or peroxide as a secondary oxidant) but didn't know how to start finding one. The process in the patent is not quite catalytic but it certainly explains how to make a permanganate bleaching bath last. Like the others, I suspect that this would be most advantageous for those trying to maintain a permanganate bleach bath rather than for one-shot use. It does look like persulfate can be added to smaller concentrations of permanganate bath to get the job done as well. Ammonium persulfate is used to etch printed circuit boards and in biochemistry to make electrophoresis gels. It is probably available at electronics hobby shops... I know it used to be. The quantities involved are pretty large, though.

Anyway, I'll be interested to hear about peoples' results with the patent method (adding persulfate and a group I or II metal salt -- though they didn't mention anything other than AgNO3, which is expensive!) in keeping a permanganate bleach bath alive. This thread has re-kindled my interest in B&W reversal, and I think I only need a few dollars' worth of chemicals to give it another shot, so why not?

Sean · Sep 29, 2004

This thread has been heavily moderated, try to keep it going on topic now, thanks

Jorge · Sep 30, 2004

well, I guess sponsors are not allowed to make fools of themselves. Anyway, thinking that reversal process cannot be all that hard, I googled it and lo an behold found many citations using permanganate as the bleach, here is one by Ilford.

http://www.ilford.com/html/us_english/pdf/reversal_web.pdf

this one, is a re-exposure one, give me some time and I will find one with chemical fogging instead of re-exposure.

Jorge · Sep 30, 2004

Ok, some more news, if sodium sulfide is used in the second developer, there is no need for re-exposure and it results in a sepia toned negative....I am getting closer, I guess I am going to unpack the rollei 35 mm and have some fun with reversal processes....

Jorge · Sep 30, 2004

Ok, last bit of news before going to bed, it seems thiourea is a good chemical fogging agent to avoid having to re expose film for direct positive results. I have to brush up on my electrochemistry to see why this is, I am sure I can figure out a good alternative. We will see but this reversal stuff does not seem to be that hard.

rjr · Sep 30, 2004

Jorge,

Jorge said:
Ok, last bit of news before going to bed, it seems thiourea is a good chemical fogging agent to avoid having to re expose film for direct positive results.

Following a discussion at Photo.net I already tried that. Thiorea works fine, but the slides are sepia stained and very warm toned - you need to like it, you need the right application for that.

Temperature and dilution of the Thiorea will influence tone.

Jorge said:
I have to brush up on my electrochemistry to see why this is, I am sure I can figure out a good alternative. We will see but this reversal stuff does not seem to be that hard.

Tin-(II)-Chloride. THats the reversal agent in the old "large" E6-kits with seperate reversal step.

But it is quite nasty, very harmful to your skin if you spill it.

Once I get my hand on a bottle of reversal agent (probably Calbe/FujiHunt) I´ll try that. it will work, I am pretty sure. But reversal by reexposure isn´t actually that difficult and problematic, I had no problems with it as long as I kept turning the reel and as I placed it in water.

Jorge · Sep 30, 2004

rjr, thanks for the info on thiourea. Tin chloride is too corrosive to have in the darkroom, so I am looking for an alternative that will not be so hard to handle. Ideally it would fog the film and result on a neutral slide, I was thinking of that, the old E6, but you know, I guess the simplest way to find out is to see what are the ingredients in Kodak's kit. I used it once and got very nice results.

Helen B · Sep 30, 2004

Tin (II) Chloride is listed in the MSDS for the E-6 reversal bath, with a propionic acid - sodium propionate buffer. I've also seen dimethylamine borane referred to, but that's not nice stuff either.

E-4 used tertiary butylamine borane (TBAB, Kodak reversal agent RA-1)
http://www.kodak.com/global/en/professional/support/techPubs/cis111/cis111.pdf
Dead Link Removed.
Also unpleasant stuff.

In the kits and packaged chemicals, these are present in tiny amounts.

According to my notes, Ron Spiers uses the following fogging agent:
Stock solution:
Potassium Borohydride (KBH4) 0.1 g
Sodium Hydroxide 10 g
Cold Water to make 100 ml

http://www.state.nj.us/health/eoh/rtkweb/1558.pdf

The working solution contains 12 ml of stock per litre. Mix immediately before use, immerse the film in it for one minute, then discard the working solution. Follow by the developer of your choice. There will be a reference on the web, I've just run out of time... more later?

Best,
Helen

Jorge · Sep 30, 2004

Helen B said:
Tin (II) Chloride is listed in the MSDS for the E-6 reversal bath, with a propionic acid - sodium propionate buffer. I've also seen dimethylamine borane referred to, but that's not nice stuff either.

E-4 used tertiary butylamine borane (TBAB, Kodak reversal agent RA-1)
http://www.kodak.com/global/en/professional/support/techPubs/cis111/cis111.pdf
Dead Link Removed.
Also unpleasant stuff.

In the kits and packaged chemicals, these are present in tiny amounts.

According to my notes, Ron Spiers uses the following fogging agent:
Stock solution:
Potassium Borohydride (KBH4) 0.1 g
Sodium Hydroxide 10 g
Cold Water to make 100 ml

http://www.state.nj.us/health/eoh/rtkweb/1558.pdf

The working solution contains 12 ml of stock per litre. Mix immediately before use, immerse the film in it for one minute, then discard the working solution. Follow by the developer of your choice. There will be a reference on the web, I've just run out of time... more later?

Best,
Helen

Are you sure it is borohydride Helen? If I recall correctly, borohydrides catch fire when mixed with water. Seems none of the choices are really safe for a home darkroom.

Jordan · Sep 30, 2004

Jorge said:
Are you sure it is borohydride Helen? If I recall correctly, borohydrides catch fire when mixed with water. Seems none of the choices are really safe for a home darkroom.

Yup, potassium borohydride is used in reversal. Borohydrides don't react with water except in acid solution and they are commonly used in water or water-alcohol mixtures for organic reductions. You're probably thinking of aluminum hydrides like LAH (lithium aluminum hydride, LiAlH4) which do react violently with water but are used for related purposes in organic chemistry.

Re: thiourea -- The re-exposure stage is just a way of getting all of the remaining silver halide reduced to a stable and opaque form of silver. Re-exposure and re-development will do it, giving you a silver positive. Another way to the same goal is using a reagent to "re-sensitize" the silver halide, which can then be re-developed without light exposure. I believe the reagent that does this is sodium dithionite but I will have to check when I get home. I think the tin salt accomplishes the same goal.

Sodium sulfide -- the toner part of sepia toner -- will create a silver sulfide positive if used for "re-development". No light re-exposure is needed as the sulfide reacts directly with the silver halide "latent positive" in the film. Thiourea is the toning component of odourless sepia toner kits and in alkaline solution basically just acts as an in situ source of sulfide ion. When toning prints, the tone thiourea gives can be controlled by the concentration of base and thiourea in the toning solution.

I've used thiourea successfully for making B&W slides and found it much easier to control than light re-exposure in home use. However, I did find that the sepia-ness of the tone in the final positive is very film-dependent under otherwise identical conditions. For example, in my tests, thiourea gave disgusting sickly yellow positives with TMX but very nice, deep chocolatey brown-black tones with Pan F Plus. This is probably due to the differences in grain structure between these two films.

I have a bunch of notes on reversal processing from the book by Grant Haist and can share recipes with anyone. Just send me a note. That resource, combined with Helen's patent-surfing, should be very helpful.

Jorge · Sep 30, 2004

Thanks Jordan, I understand the chemistry, is actually very simple. After the first developer, we have a "negative" image made of metallic silver, we then dissolve this metallic silver with the bleach and are left with ionic silver. The re exposure step is nothing more than re activating a latent image to be developed once again.

My concern is that apparently reducers powerful enough like boronhydride, tin chloride, etc are not exactly safe chemicals to have at home. I guess the re exposure step is the way to go, but I am curious as to what is Kodak using on their direct positive kit for Tmx, as I said, I used it once and it was simple to use, no re exposure needed. OTOH they might be using a very powerful reducer in very small quantities.

(which BTW, I am not so sure boronhydride is not water reactive, perhaps not as much as the lithium hydrides, but I distinctly recall using some boronhydride to make a demonstration to field techs about water reaction. Anyway, no matter)

Jordan · Sep 30, 2004

Jorge, I'm not certain of this, but it's likely that the Kodak kit uses dithionite or something like it. Tin chloride is used in home E6 kits IIRC. Thiourea is probably the least offensive way of making the positive, aside from re-exposure and re-development, though -- it's toxic but only small quantities are required.

Some borohydrides are probably more reactive than others. Lithium borohydride will reduce esters of relatively active carboxylic acids while sodium borohydride will not. I would expect potassium borohydride to be even less reactive. This is solely a polarizing effect of the metal ion. Borohydrides will definitely react with acidic solutions of water but as I mentioned, in base it is fine. I have used it in (IIRC) a water-dioxane mixture. Boranes (neutral gases) are probably more water-sensitive though.

Jorge · Sep 30, 2004

Jordan said:
Jorge, I'm not certain of this, but it's likely that the Kodak kit uses dithionite or something like it. Tin chloride is used in home E6 kits IIRC. Thiourea is probably the least offensive way of making the positive, aside from re-exposure and re-development, though -- it's toxic but only small quantities are required.

Some borohydrides are probably more reactive than others. Lithium borohydride will reduce esters of relatively active carboxylic acids while sodium borohydride will not. I would expect potassium borohydride to be even less reactive. This is solely a polarizing effect of the metal ion. Borohydrides will definitely react with acidic solutions of water but as I mentioned, in base it is fine. I have used it in (IIRC) a water-dioxane mixture. Boranes (neutral gases) are probably more water-sensitive though.

Yeah, you are right, it seems thiourea is the least offensive one. The thing is, you notice this is an organic compound as opposed to the metallic ones, can you think of any other powerful organic reducers, how about any amine derivates, you seem to have more knowledge about this than I do.

Helen B · Sep 30, 2004

EK list dimethylamine borane in the MSDS for the T-Max 100 Direct Positive kit redeveloper.

What about the suggestion Patrick made earlier: sodium hydrosulphite with sodium carbonate?

How do we assess the performance of chemical fogging agents? In addition to comparison of the image quality, you could use the density produced by light fogging as the benchmark for a quantifiable comparison, ie does the chemical fogging produce the same density as light fogging?

But do we always need maximum density? For some purposes high-as-possible D-max may not be ideal and chemical fogging may offer more control over shadow densities. Im just thinking aloud about the reasons I wanted to re-examine the reversal process for my own purposes.

Best,
Helen

Jorge · Sep 30, 2004

Thank you Helen, dimethylamine borane uh? Seems to me this is going to be a hard chemical to find, at least outside industrial applications. Perhaps you are right and giving a shot to Gainer's idea cannot hurt.

You all can correct me if I am wrong, but it seems to me that we have two different processes here. With re exposure, we are oxidizing the remaining silver ions (just as if we were making an exposure for the first time) to then be reduced by the second developer. With direct positive, we are using a powerful enough reducer to go directly to silver metal without having to excite the silver ions. I cannot beleive there is not a more accesible reducer that will form a complex with silver given the correct time and temperature.

In any case, it seems to me both methods should yield similar results, after all, all we are dealing with is the left over silver ions. I suppose we could expose a step tablet onto the film and judge the density range results given by both methods.

Jordan · Sep 30, 2004

Okay, I've just had a chance to look through my notes from Haist's book. Turns out that sodium dithionite and sodium hydrosulfite are one and the same. He provides a formula for a fogging re-developer:

Kodak Fogging Developer FD-70

Part A: Sodium dithionite, 90%........ 5.0 g
Part B: Water ..... 900 ml
Kodalk Balanced Alkali ..... 10.0 g
2-Thiobarbituric acid ..... 0.5 g
Water to make ..... 1.0 l

Dissolve the 5 g of part A into one liter of part B not more than 2 hr before use. Discard after one use.

This stuff apparently works very quickly (~1 min at 20C).

He also makes a few other comments relevant to our discussion. The first is that dichromate bleaches exert a hardening effect on emulsions, while permanganates exert a softening effect. Dichromates are also more likely to permanently stain the emulsion. Permanganates de-sensitize the unbleached silver halide more, but the sensitivity can be partially restored through the use of a sulfite-containing clearing bath (metabisulfite in the case of a permanganate bleach). Haist also lists a number of alternative fogging agents, such as hydrazines, various boranes (as we have been discussing), thiourea dioxide (nasty), and others.

As to measuring the efficiency of fogging, I do not know. Seems like a densitometer would be the way to go with that.

My likely supplier, Fotochem in St-Hubert, Quebec, sells pretty much all of these chemicals. Thiourea is cheap -- tin (II) chloride costs eight times more and sodium dithionite 10 times more per gram, and these can only be used one-shot IIRC. Potassium borohydride is prohibitively expensive.

gainer · Sep 30, 2004

The dithionite may be expensive, but Super Iron Out is not. It contains sodium hydrosulfite (dithionite) and sodium carbonate. I think it will reduce the haliide out of the silver without the other stuff. I'll try it again to find out. any piece of exposed or unexposed film should tell the story.

Jorge · Oct 1, 2004

Jordan, great info! but after our discussion it seems the best way to go about it is the re exposure route. Having to deal with thionils or boranes is not something I want to do at home, even with my experience handling haz materials. All of these compounds are extremely corrosive and most certainly even a drop will burn skin tissue, is not worth the risk.

In addition, it seems the expense and most likely the hassle to obtain these chemicals is not worth it just to do some experimenting. There are times when I think printing some of my negatives as a negative on pt/pd would make a cool image, but for contact printing I dont need small grain, I only need DR. Seems I can get it by using the re exposure method.

Gainer's idea of using super iron out has a lot of merit, unfortunately I cannot get it here, so I am going to go with the re exposure route, and will post the results. If anybody has any other ideas, please post them, I would like to hear them.

gainer · Oct 1, 2004

gainer said:
The dithionite may be expensive, but Super Iron Out is not. It contains sodium hydrosulfite (dithionite) and sodium carbonate. I think it will reduce the haliide out of the silver without the other stuff. I'll try it again to find out. any piece of exposed or unexposed film should tell the story.

It needs either light or the thiobarbituric acid. If you expose the film after bleaching out the negative image, you can use any developer that you might use on paper. If you want a solution that saves the trouble of exposing, add a little bit of the barbituric acid to a solution of Super Iron Out.
The trouble might be, if the name is a clue, that the barbituric acid is as much a controlled substance as the barbiturates. I think we should find another way to cause chemical exposure.

Permanganate reversal baths

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