B&W reversal: Thiocyanate or Thiosulfate

pkr1979 · Dec 25, 2020

Merry Christmas all,

I've developed different fims in the bw reversal process never using any thiocyanate or thiosulfate. I’ll now try to develop Tmax100 and 400 according to the Hans Dietrich recipe:
EDITED LINK (previous was not complete instructions):
https://www.freestylephoto.biz/pdf/product_pdfs/formulary/FormularyReversalTmax_010600.pdf

What Id like to know is why this recipe use thiosulfate instead of thiocyanate? As far as I understand thiocyanate is preferrable? I know there are older Kodak recipes using thiocyanate and I assume this Dietrich knew that and had his reasons for choosing thiosulfate instead. Maybe this is documented in the 1988 March/April issue of Darkroom Techniques but I cant find that publication.

Im thinking that maybe Tmax and that kind of grain films prefer thiosulfate over thiocyanate? Any knowledge/suggestions anyone?

Cheers
Peter

relistan · Dec 25, 2020

Welcome!

pkr1979 said:
Im thinking that maybe Tmax and that kind of grain films prefer thiosulfate over thiocyanate? Any knowledge/suggestions anyone?

I don't know the answer from a chemical perspective but I've done a lot of reading recently and it seems that both are used. I saw somewhere a recommendation that if you used thiosulfate in place of thiocyanate that you ought to use about 2x the amount. However, my recent experience experimenting with sodium thiosulfate suggests that you start with a much lower amount than you think. Especially if you don't have a really short first developer time. Not sure it answers your question, but maybe useful insight.

EDIT These may be useful:

Kodak publication J-6: https://imager.ie/image/posts/black-and-white-reversal-with-hydrogen-peroxide/j6.pdf
A PDF I have of Hans Dietrich's article: https://imager.ie/image/posts/black...-peroxide/ReversalProcessing-HansDietrich.pdf

You may also be interested in this active thread where we're experimenting with reversal using hydrogen peroxide and vinegar: https://www.photrio.com/forum/threads/b-w-reversal-with-hydrogen-peroxide.180091/

pkr1979 · Dec 25, 2020

Thanks!

And thanks so much for those pdfs! Ive been searching for that Dietrich stuff - I really appreciate this man

Slainte
Peter

pkr1979 · Dec 25, 2020

The Dietrich article is interesting... I didnt know hydroquinone altered contrast, maybe it does so for regular bw developing to then.

However, he doesnt say why he went for thiosulfate instead of thiocyanate. He is referring to d67 though, for higher contrast... which has thiocyanate. Maybe he just tried with thiosulfate and saw it worked well.

relistan · Dec 25, 2020

pkr1979 said:
Thanks!

And thanks so much for those pdfs! Ive been searching for that Dietrich stuff - I really appreciate this man

Slainte
Peter

No problem! You might also be interested in Jens Osbahr's process using Rodinal: https://imager.ie/image/posts/black-and-white-reversal-with-hydrogen-peroxide/osbahr_reversal.pdf

pkr1979 said:
The Dietrich article is interesting... I didnt know hydroquinone altered contrast, maybe it does so for regular bw developing to then.

I'm sure some real experts will chime in here, but here's my understanding. Hydroquinone is a high contrast developing agent. But it is only active at a certain pH (can't remember, something like 9). Below that it only acts in a superadditive capacity with the other developing agent—in this case metol—instead of also developing on its own. By putting sodium carbonate into the D-76, Dietrich is raising the pH high enough that the hydroquinone will become active as well. This will substantially increase the contrast, and the higher pH will increase the activity in general. It will also increase the grain. A popular D-76 variant (D-76H) leaves out the hydroquinone entirely.

Anyway, I am not sure exactly what Dietrich meant by varying the hydroquinone, but I imagine that up to a certain point adding more will increase contrast.

pkr1979 said:
However, he doesnt say why he went for thiosulfate instead of thiocyanate. He is referring to d67 though, for higher contrast... which has thiocyanate. Maybe he just tried with thiosulfate and saw it worked well.

I am not sure that the thiosulfate choice vs thiocyanate affects contrast at all. My guess is they are equivalent but maybe one is faster acting than the other (would guess thiocyanate is). The idea is to introduce enough solvent to help clear highlights, without overly suppressing the darkest shadows (remember they will be inverted later). I recently found out that David Wood at DR5 doesn't use any solvent in his first developer. I've been developing without it so far but will try adding it also. My first experiment with thiosulfate in the first developer left me with mostly blank film.

@Raghu Kuvempunagar might have more to say about this, if he's around.

Lachlan Young · Dec 25, 2020

If you use acidified permanganate as your bleach, you do not want to use thiocyanate containing developer - you can create HCN gas. This is why thiosulphate, DTOD, and various development accelerators are used in formulae recommended for use with permanganate bleaches. While the quantities potentially created of HCN may be small, it's really not worth risking it.

The point of these additives in powerful, high activity developers is to access and force development of all the silver to get good highlights after reversal. Some of the more high tech first developers use accelerators in preference to silver solvents to do this.

Whatever DR5's claims are (or aren't), you're better off starting from the research Agfa and others did on first developers, they're rather more significantly based in useful scientific reality rather than on fanciful marketing based on Dmax your eyes can't use.

Raghu Kuvempunagar · Dec 25, 2020

pkr1979 said:
What Id like to know is why this recipe use thiosulfate instead of thiocyanate? As far as I understand thiocyanate is preferrable?

Dietrich might have found that his first developer formula would need, for TMax films, substantial amount of thiocyanate to give the results he was aiming at, i.e. "the aim point for best screen quality of a good black-and-white slide is a 0.2 density above the base, negligible fog and an approximate maximum density ranging from 2.2 to 2.6.". His formula uses 16g of thiosulphate and at the recommended substitution of 2g of thiousulphate for 1g of thiosulphate, he would have needed to use ~8g of thiocyanate in his first developer, which might scare the hell out of many home users. Only Dietrich knows the real reason for his choice of thiosulphate and I'm just guessing here.

In the literature, thiocyanate is the preferred halide solvent. Also, if the first developer is to be reused, thiosulphate can make it unstable.

Raghu Kuvempunagar · Dec 26, 2020

relistan said:
I've been developing without it so far but will try adding it also. My first experiment with thiosulfate in the first developer left me with mostly blank film.

Going by your own results, Fomapan 400 shot at box speed, would need very little thiosulphate. You might want to try just 1g/l in your first developer and see what you get. TMax films would definitely need a lot more, but the nice thing about using a kit formulated for specific films, like the one OP is planning to use for TMax films, is that you don't need to experiment - just follow the instructions strictly and you'll get consistent results.

pkr1979 · Dec 26, 2020

Thanks for the feedback all,

I think the Osbahr process was one of the first recipes I came across… either that or the Ilford. I use stannous chloride instead of re-exposure… but as a bath before the second developer.

I’ve also suspected that the TMax films require more silver solvent than many other films. Maybe this is a reason for opting for thiosulfate… that its easier to control when ‘more than normal’ is needed... In addition to being better to combine with permanganate bleach. I was considering using thiocyanate instead of thiosulfate as some claim it gives finer grains and is ‘better’. I’ve got both permanganate and dichromate so I could go either way… Im probably just going for thiosulfate but with dichromate bleach. I wonder what 8g og thiocyanate would do instead though… If I get the results I want with Dietrich standard recipe I’ll probably never know ;-)

Raghu Kuvempunagar · Dec 26, 2020

pkr1979 said:
If I get the results I want with Dietrich standard recipe I’ll probably never know ;-)

You might want to first check and confirm that Dietrich's formula as given in the pdf file is correct. It mentions, oddly, the presence of Sodium sulfate (anhydrous) 100 g. This could be a mistake as there is no sodium sulfite in the formula. Sodium sulfate is generally used to reduce the swelling of emulsion and an odd choice. Your result will not be the same if you use one in place of the other.

pkr1979 · Dec 26, 2020

I think you are right. I think its supposed to be Sodium Sulfite 100 grams. I corrected the link in the first post:
https://www.freestylephoto.biz/pdf/product_pdfs/formulary/FormularyReversalTmax_010600.pdf

relistan · Dec 26, 2020

Lachlan Young said:
If you use acidified permanganate as your bleach, you do not want to use thiocyanate containing developer - you can create HCN gas. This is why thiosulphate, DTOD, and various development accelerators are used in formulae recommended for use with permanganate bleaches. While the quantities potentially created of HCN may be small, it's really not worth risking it.

Very good point. I had seen that mentioned and since I wasn't using a permanganate bleach I had put it out of mind.

Lachlan Young said:
Whatever DR5's claims are (or aren't), you're better off starting from the research Agfa and others did on first developers, they're rather more significantly based in useful scientific reality rather than on fanciful marketing based on Dmax your eyes can't use.

Yes, agreed. Also the Agfa patent seems to have a lot of detail if you can penetrate it. I saw another thread where you called out some interesting facts (e.g. the PEG in the first developer)

relistan · Dec 26, 2020

Raghu Kuvempunagar said:
You might want to first check and confirm that Dietrich's formula as given in the pdf file is correct. It mentions, oddly, the presence of Sodium sulfate (anhydrous) 100 g. This could be a mistake as there is no sodium sulfite in the formula. Sodium sulfate is generally used to reduce the swelling of emulsion and an odd choice. Your result will not be the same if you use one in place of the other.

Good catch, I just dug out the PDF but didn't check it. Definitely wrong. I'll correct it in the one I linked.

gorbas · Dec 26, 2020

My last BW reversal processing was 30 years ago. Back then I was under impression that function of the silver solvents is to control grain shape and size in processing of 8 and 16mm cine films.
Yesterday I was going thru "Photographic facts and formulas book" and finally found sound explanation of function of thiocyanate or thiosulfate in the first developer. Maybe it will help you?
[

Lachlan Young · Dec 26, 2020

relistan said:
the Agfa patent seems to have a lot of detail if you can penetrate it. I saw another thread where you called out some interesting facts (e.g. the PEG in the first developer)

There's actually quite a long list of known development accelerators - the trouble is finding one that works well with the developer you wish to use.

relistan · Dec 26, 2020

gorbas said:
Yesterday I was going thru "Photographic facts and formulas book" and finally found sound explanation of function of thiocyanate or thiosulfate in the first developer. Maybe it will help you?

Very interesting! Thanks.

Raghu Kuvempunagar · Dec 26, 2020

gorbas said:
Yesterday I was going thru "Photographic facts and formulas book" and finally found sound explanation of function of thiocyanate or thiosulfate in the first developer.

The function of halide solvent in the first developer is very well explained with substantial technical details in the chapter on reversal processing in Haist volume 2. Worth reading if you are interested.

Raghu Kuvempunagar · Dec 26, 2020

Development accelerator is not a substitute for halide solvent. In fact, the Agfa patent that is often touted in this forum as the state of the art in reversal processing itself uses both thiocyanate (halide solvent) and PEG (development accelerator) in the first developer proposed in the patent!

gorbas · Dec 26, 2020

Raghu Kuvempunagar said:
The function of halide solvent in the first developer is very well explained with substantial technical details in the chapter on reversal processing in Haist volume 2. Worth reading if you are interested.

Sorry Raghu, I never managed to read Haist book. Is there .pdf version of it for download? Is my head going to explode from reading it?

Raghu Kuvempunagar · Dec 26, 2020

gorbas said:
Sorry Raghu, I never managed to read Haist book. Is there .pdf version of it for download? Is my head going to explode from reading it?

Goran: Yes there is pdf of both volumes on some Facebook group on darkroom processing. No idea if the group has consent from the publisher to make these files available to the group's members.

It's a very readable book even for the non technically inclined. Lots of interesting stuff demystifying many aspects of photochemistry.

Anon Ymous · Dec 26, 2020

Raghu Kuvempunagar said:
Goran: Yes there is pdf of both volumes on some Facebook group. Let me DM you the link tomorrow.

It's a very readable book even for the job technically inclined. Lots of interesting stuff demystifying many aspects of photochemistry.

Does one need to be a Facebook member to grab these pdf files?

Lachlan Young · Dec 26, 2020

Raghu Kuvempunagar said:
Development accelerator is not a substitute for halide solvent. In fact, the Agfa patent that is often touted in this forum as the state of the art in reversal processing itself uses both thiocyanate (halide solvent) and PEG (development accelerator) in the first developer proposed in the patent!

Again, you aren't reading the patent very well. The MQ developer quoted as 'a commercially available product' has no thiocyanate, but the one that is proposed using an HQMS salt & Dimezone-S (and derived from E-6 FD) does have thiocyanate in it. The MSDS for Kodak's T-Max reversal kit indicates it also uses PEG, but no thiocyanate - which would definitely have been disclosed if it was used.

The commercial aim may have been to enable a closer linkage between E-6 and Scala developer component manufacture, but the move away from dichromate bleaches for BW reversal may have put paid to that.

pkr1979 · Dec 26, 2020

Thanks for info gorbas! I might actually try that recipe with thiocyanate instead. I guess using 8 g is the way to start. I figured Id keep the first developer time. Maybe the effective film speed will be faster... From what Ive read people expose tmy2 at 160-240 for this kit as is.

Raghu Kuvempunagar · Dec 26, 2020

pkr1979 said:
I might actually try that recipe with thiocyanate instead. I guess using 8 g is the way to start. I figured Id keep the first developer time. Maybe the effective film speed will be faster... From what Ive read people expose tmy2 at 160-240 for this kit as is.

The Dietrich document you shared recommends EI of 400 for TMax 400 if I understood it correctly: "Excellent continuous tone black-and-white slides, anyone? Try T-Max. You can't imagine how great it is working with E.I.s 100 and 400". In any case, you might want to first experiment with a small test strip before you try it on a whole roll of film.

pkr1979 · Dec 27, 2020

I saw that, but Im not sure if he is referring to the 100 and 400 film or the way to expose them... I think youd need an extra stop. The folks in this thread followed the recipe:
https://www.photrio.com/forum/threa...mulary-reversal-kit-and-tmax-400-tmy-2.74132/
But are giving it more light.

B&W reversal: Thiocyanate or Thiosulfate

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