B&W reversal: Thiocyanate or Thiosulfate

DeletedAcct1 · Jan 6, 2021

pkr1979 said:
OK. What about before permanganate bleach was used... why didnt they use thiosulfate then? It seems to me that because of the permanganate bleach this isnt really a choice... but if there is a choice thiocyanate is preferrable?

Historically, even before dichromate, it was permanganate only.
Actually, the inventor of the use of permanganate in a b&w reversal process was an italian chemist in the early 1900.
Unfortunately a bad formulated permanganic acid bleach causes damage to the subbing layer and not on the emulsion itself. Prove being that the damage are flakes of gelatine, that would mean the gelatine hasn't melted at all.
A melted gelatine is another thing, it doesn't come off in flakes, it just melts.
Unfortunately not all films are using an appropriate subbing layer to resist a permanganic acid bleach, but one that is carefully formulated, plus the use of hexametaphosphate, doesn't cause any damage at all.

pkr1979 · Jan 6, 2021

What about bromide?

Here: https://www.photrio.com/forum/resources/kodak-b-w-reversal-processing-formulae.191/
there are recipes for both first and second developers with and without bromide.

I know its a restrainer but not much more of the effect of bromide. when is it useful, when is not? or for what films is it useful or not useful for? The formulae suggest D168 (no bromide) for continuous tone films (like Tmax400 i suppose), and D67 (with bromide) for films like Panatomic-X... I assumed D67 would suit a film like TMax400 well... maybe I'm interpreting it wrong.

Lachlan Young · Jan 6, 2021

pkr1979 said:
What about bromide?

Here: https://www.photrio.com/forum/resources/kodak-b-w-reversal-processing-formulae.191/
there are recipes for both first and second developers with and without bromide.

I know its a restrainer but not much more of the effect of bromide. when is it useful, when is not? or for what films is it useful or not useful for? The formulae suggest D168 (no bromide) for continuous tone films (like Tmax400 i suppose), and D67 (with bromide) for films like Panatomic-X... I assumed D67 would suit a film like TMax400 well... maybe I'm interpreting it wrong.

I don't think there's any great theory here - the KBr is there to suppress overall fog in a faster developing film - and probably get the FD time to longer than 5 minutes to hopefully ensure even development. It'll probably work equally well with a faster film, but the FD time might be quite long. The main thing to understand is that you have to balance off getting the silver accessed & developed fully before the overall fog level rises too high.

pkr1979 · Jan 7, 2021

Lachlan Young said:
I don't think there's any great theory here - the KBr is there to suppress overall fog in a faster developing film - and probably get the FD time to longer than 5 minutes to hopefully ensure even development. It'll probably work equally well with a faster film, but the FD time might be quite long. The main thing to understand is that you have to balance off getting the silver accessed & developed fully before the overall fog level rises too high.

Thanks for this.

Raghu Kuvempunagar · Jan 8, 2021

pkr1979 said:
if there is a choice thiocyanate is preferrable?

This work used Kodak D-19 + potassium thiocyanate 5g/l as the first developer, 10minutes @20C for reversing TMax 100 film:
https://unblinkingeye.com/Articles/NDICRB/ndicrb.html

pkr1979 · Jan 28, 2021

So, I gave the Dietrich-recipe a try... some changes to the original was applied (both intended and unintended).
1. Silly mistake... the times he has given is for development with agitation each minute for ten minutes. I use a Jobo and should have reduced the development time to 8 min 30 sec.
2. The second developer was mixed 1+3 instead of 1+2. This wasnt deliberate when mixing, but I was aware of it when developing. I chose not to change it as I have heard rumours Dektol 1+2 might give a yellow tint and I wanted to avoid this. I dont know if it is the case though. I extended the time for the second developer.
3. I used thiocyanate instead of thiosulfate. This was intended.
4. I used dichromate bleach instead of permanganate. This was also intended.
5. I use a chemical re-exposure bath with stannous chloride. Intended.

The slides... I should probably attach some scans but as of now... TMax 100 didnt really work out. It was way to flat. No blacks and no whites. TMax 400 was way better (at about 200iso - I exposed at 100, 200 and 400), it has proper blacks and proper white... but it lacks 'volume' or midtones. Its also a bit grainy and maybe not so sharp.

- Im not sure what to blame (instead of myself) but as far as I understand thiocyanate (and thiosulfate) kills midtones.
- Maybe its the overdeveloping.
- Or maybe to weak second developer. But doubt that. Ive used the 1+3 dilution with very sharp results and little grain previously for TMax400.

I'll keep on with this developer for a few more rounds to se if it can be improved. Out of the 5 variables Ive changed I'll keep using the chemical re-exposure bath, and the dichromate bleach (Im never using permanganate again actually). I will continue trying with thiocyanate. But I'll shorten the development time for the first developer to 8 min 30 sec. I havent decided if I'll delute the Dektol (second developer) to 1+2 or 1+3... And, Im either exposing 100+200... or 160 straight (400 is too dark).

If I dont get anywhere with this I'll try D-19 instead.

relistan · Jan 28, 2021

pkr1979 said:
So, I gave the Dietrich-recipe a try... some changes to the original was applied (both intended and unintended).
1. Silly mistake... the times he has given is for development with agitation each minute for ten minutes. I use a Jobo and should have reduced the development time to 8 min 30 sec.
2. The second developer was mixed 1+3 instead of 1+2. This wasnt deliberate when mixing, but I was aware of it when developing. I chose not to change it as I have heard rumours Dektol 1+2 might give a yellow tint and I wanted to avoid this. I dont know if it is the case though. I extended the time for the second developer.
3. I used thiocyanate instead of thiosulfate. This was intended.
4. I used dichromate bleach instead of permanganate. This was also intended.
5. I use a chemical re-exposure bath with stannous chloride. Intended.

The slides... I should probably attach some scans but as of now... TMax 100 didnt really work out. It was way to flat. No blacks and no whites. TMax 400 was way better (at about 200iso - I exposed at 100, 200 and 400), it has proper blacks and proper white... but it lacks 'volume' or midtones. Its also a bit grainy and maybe not so sharp.

- Im not sure what to blame (instead of myself) but as far as I understand thiocyanate (and thiosulfate) kills midtones.
- Maybe its the overdeveloping.
- Or maybe to weak second developer. But doubt that. Ive used the 1+3 dilution with very sharp results and little grain previously for TMax400.

I'll keep on with this developer for a few more rounds to se if it can be improved. Out of the 5 variables Ive changed I'll keep using the chemical re-exposure bath, and the dichromate bleach (Im never using permanganate again actually). I will continue trying with thiocyanate. But I'll shorten the development time for the first developer to 8 min 30 sec. I havent decided if I'll delute the Dektol (second developer) to 1+2 or 1+3... And, Im either exposing 100+200... or 160 straight (400 is too dark).

If I dont get anywhere with this I'll try D-19 instead.

Very interesting, would like to see the results if you have anything you'd be willing to post. Over development in the first developer will lead to general fog and so reduced Dmax and reduced midtones. You might try the same exact setup again without the over delopment and see if that improves things. The dilution of the second developer shouldn't matter that much as long as you run it long enough to develop to completion.

Raghu Kuvempunagar · Jan 28, 2021

pkr1979 said:
- Im not sure what to blame (instead of myself) but as far as I understand thiocyanate (and thiosulfate) kills midtones.

Excess thiocyanate in the first developer and excessive agitation do produce very flat positives. Try reducing thiocyanate (by 50%) and use intermittent inversion agitation, keeping everything else the same as before. Depending on the results, tune the amount of thiocyanate further. You should be able to reach a good ballpark in 2-3 trials.

relistan · Jan 29, 2021

Raghu Kuvempunagar said:
Excess thiocyanate in the first developer and excessive agitation do produce very flat positives. Try reducing thiocyanate (by 50%) and use intermittent inversion agitation, keeping everything else the same as before. Depending on the results, tune the amount of thiocyanate further. You should be able to reach a good ballpark in 2-3 trials.

This is a good point because he doesn’t say how much he used. Correct meif I’m wrong but AFAIK you need less thiocyanate than thiosulfate so you can’t switch the recipe gram for gram.

Raghu Kuvempunagar · Jan 29, 2021

relistan said:
This is a good point because he doesn’t say how much he used. Correct meif I’m wrong but AFAIK you need less thiocyanate than thiosulfate so you can’t switch the recipe gram for gram.

I think the suggested approximation is 1g of thiocyanate for 2g of thiosulphate which translates to 8g of thiocyanate per liter of Dietrich's first developer. It's probably a little too much. But agitation plays an important role here and I have found that thiocyanate does more damage than good when the agitation is continuous and/or aggressive. Intermittent inversion agitation works best for me.

pkr1979 · Jan 29, 2021

Hi fellas,

And thanks

relistan said:
Over development in the first developer will lead to general fog and so reduced Dmax and reduced midtones. You might try the same exact setup again without the over delopment and see if that improves things.

This has to be at least partly the case, at least. Im probably dropping first development to 8:30.

relistan said:
This is a good point because he doesn’t say how much he used. Correct meif I’m wrong but AFAIK you need less thiocyanate than thiosulfate so you can’t switch the recipe gram for gram.

I should have mentioned this. I used 5g thiocyanate per liter. This is based on the standard suggestion when using thiocyanate with D-19.

Raghu Kuvempunagar said:
Excess thiocyanate in the first developer and excessive agitation do produce very flat positives. Try reducing thiocyanate (by 50%) and use intermittent inversion agitation, keeping everything else the same as before.

Im using a Jobo so I cant really do intermittent agitation, but I can turn down the rotation speed substantially... I assume that will help? Also... wouldnt reducing the time of the first developer have the same effect as reducing the thiocyanate?

Im a little reluctant to change too many things at the same time.

Cheers
Peter

Raghu Kuvempunagar · Jan 29, 2021

pkr1979 said:
Im using a Jobo so I cant really do intermittent agitation, but I can turn down the rotation speed substantially... I assume that will help? Also... wouldnt reducing the time of the first developer have the same effect as reducing the thiocyanate?

Not having used Jobo ever, I can't speak from experience though it is plausible that reducing rotation speed reduces the activity of thiocyanate. To keep things simple, you might want to keep the development time unchanged and reduce the rotation speed. If the results turn out to be similar to what you got earlier, then you know that thiocyanate needs to be decreased.

pkr1979 · Jan 29, 2021

Raghu Kuvempunagar said:
Not having used Jobo ever, I can't speak from experience though it is plausible that reducing rotation speed reduces the activity of thiocyanate. To keep things simple, you might want to keep the development time unchanged and reduce the rotation speed. If the results turn out to be similar to what you got earlier, then you know that thiocyanate needs to be decreased.

If I change just one thing I'll change development time as I know its too long... Im tempted to do both ;-)

Raghu Kuvempunagar · Jan 29, 2021

pkr1979 said:
Im tempted to do both ;-)

Whatever works.

pkr1979 · Jan 30, 2021

Raghu Kuvempunagar said:
But agitation plays an important role here and I have found that thiocyanate does more damage than good when the agitation is continuous and/or aggressive. Intermittent inversion agitation works best for me.

@Raghu Kuvempunagar, Im not doubting you, but do you have any idea why?

Raghu Kuvempunagar · Jan 31, 2021

pkr1979 said:
@Raghu Kuvempunagar, Im not doubting you, but do you have any idea why?

Page #322-323 in Haist volume 2 gives an explanation of what happens when thiocyanate is used in the first developer. My guess is aggressive agitation develops mid tones faster and thereby creates the necessary condition for accelerated solubilization of the unexposed silver halides in the mid tones.

pkr1979 · Feb 1, 2021

Thanks. Im gonna take a walk on the wild side here and make 2 adjustments at once... I'll lower both 1st developer time and rotation speed ;-)

Lachlan Young · May 15, 2023

Tsubasa said:
Maybe the Kodak FD used DTOD as the solvent, and maybe DTOD is omitted in MSDS...

PEG is a development accelerator (via enhancing gelatin swell) - which in this context achieves the same as using a silver solvent, without the potential issues a silver solvent may cause with a modern B&W emulsion structure.

Lachlan Young · May 15, 2023

Tsubasa said:
Can it be used in a commercial FD such as Ilford PQ Universal?

On the understanding that it might not deliver an optimal or good result.

Lachlan Young · May 16, 2023

Tsubasa said:
Ok. Reversal is not for me. Too much variables in game, too much trials and waste of expensive films. To have, finally, slides that are a pita to set up the projector to look at.
I'm a casual shooter but I'm also a casual viewer. Photos, to me, are to be simple to view. No need to set up viewing screens, projectors etc...

The alternative is to contact print your neg on to Kodak 2302 (or similar print film) - that way you can get a projectable transparency, and all the benefits of neg/ pos systems. Ilford Ortho+ in Phenisol is another way to the same end if you work in bigger formats.

koraks · May 16, 2023

Tsubasa said:
To have, finally, slides that are a pita to set up the projector to look at.

Then why inquire into making slides in the first place?

tustel · Oct 11, 2023

So I've been doing BW reversal in the last 4 months for 135, 120 and 4x5 films. I have/need some questions/confirmations:

- there is no way to do it without bleach, even adding Thiocyanate in first developer?
- the way to scrap Dichromate bleach is by mixing it with clearing bath before pouring them? Or is there a better way?
- what is the hardest film type to do reversal with according to your experiences?

Anon Ymous · Oct 11, 2023

@tustel If you don't use bleach, the negative image developed by the first developer will remain on the film, you definitely don't want this.

koraks · Oct 11, 2023

tustel said:
- there is no way to do it without bleach, even adding Thiocyanate in first developer?

Correct. The concept of B&W reversal revolves around completely developing and removing the negative image and then developing the remaining silver halide in the film to obtain the positive image.

tustel said:
- the way to scrap Dichromate bleach is by mixing it with clearing bath before pouring them? Or is there a better way?

The best way is to not use it at all, of course. There are alternatives, such as permanganate, which is already a lot less harmful, and some have success with peroxide + acid. Dichromate is really nasty and should be handled with care. In Europe, it's even not legally available anymore to the general public, and I think for good reasons. So avoidance is the best remedy.

If you must use dichromate, then it's important to reduce the hexavalent chromium (Cr6+) to trivalent chromium (Cr3+) which is far less dangerous. There are many ways to do this; popular ways in photography include adding sulfite, bisulfite or ascorbic acid (vitamin C) to a solution containing Cr6+ ions. If you use a reversal chemistry set with a sulfite or bisulfite clearing bath, this can indeed be mixed with the chromium bleach before disposing of it.

And welcome to Photrio!

tustel · Oct 11, 2023

Anon Ymous said:
@tustel If you don't use bleach, the negative image developed by the first developer will remain on the film, you definitely don't want this.

koraks said:
Correct. The concept of B&W reversal revolves around completely developing and removing the negative image and then developing the remaining silver halide in the film to obtain the positive image.

That's what I thought.
Was curious because Stefan's E6 formula has thiocyanate and wondered if I could use it. Apparently no.
Thank you for confirming.

koraks said:
The best way is to not use it at all, of course. There are alternatives, such as permanganate, which is already a lot less harmful, and some have success with peroxide + acid. Dichromate is really nasty and should be handled with care. In Europe, it's even not legally available anymore to the general public, and I think for good reasons. So avoidance is the best remedy.

If you must use dichromate, then it's important to reduce the hexavalent chromium (Cr6+) to trivalent chromium (Cr3+) which is far less dangerous. There are many ways to do this; popular ways in photography include adding sulfite, bisulfite or ascorbic acid (vitamin C) to a solution containing Cr6+ ions. If you use a reversal chemistry set with a sulfite or bisulfite clearing bath, this can indeed be mixed with the chromium bleach before disposing of it.

Tried peroxide with no success.
I'll see if I can get permanganate easily here and use it as reversal bleach.

Yes, I use sulfite as clearing bath.

koraks said:
And welcome to Photrio!

Thank you! Been lurking around here

B&W reversal: Thiocyanate or Thiosulfate

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