B&W Reversal Processing: fogging/nucleating agent for second development

Raghu Kuvempunagar · Jan 30, 2021

Raghu Kuvempunagar submitted a new resource:

B&W Reversal Processing: fogging/nucleating agent for second development - A thiourea based nucleating bath for use in place of stannous chloride in B&W reversal processing.

A key step in B&W reversal processing is the formation of the positive image by A) sensitizing the residual silver halides and B) reducing the thus sensitized silver halides to silver. Though it is possible to do both A and B in a single step involving the use of a fogging redeveloper like sodium dithionite, there is some merit in keeping them separate as it allows the use of a B&W developer of the user's choice.

Sensitizing of the residual silver halides can be done either by light...

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relistan · Feb 1, 2021

Interesting, thanks for sharing!

ProfessorC1983 · Jun 5, 2021

Hi, is the 40ml of glacial acetic acid per 1L of stock solution? Which is then diluted 1:100 for working use?

Raghu Kuvempunagar · Jun 5, 2021

ProfessorC1983 said:
Hi, is the 40ml of glacial acetic acid per 1L of stock solution? Which is then diluted 1:100 for working use?

You need to use the following composition to prepare a liter of nucleating bath:
Water: 960ml
Glacial Acetic Acid: 40ml
Thiourea: 0.5g

If you have 5% Thiourea solution, then the following composition should work well:
Water: 950ml
Glacial Acetic Acid: 40ml
Thiourea 5% Solution: 10ml

Hope this was helpful.

ProfessorC1983 · Jun 5, 2021

Excellent, that was my assumption but I appreciate the confirmation. Will be trying this soon and will let you know how it goes!

Raghu Kuvempunagar · Jun 5, 2021

ProfessorC1983 said:
Excellent, that was my assumption but I appreciate the confirmation. Will be trying this soon and will let you know how it goes!

Fantastic! Will be curious to know your results when you have them.

NedL · Jun 5, 2021

Thank you for posting this, it's very interesting.
My paper developer is loaded with bromide ( since I use it replenished )... but might give it a try anyway to see what happens.

Raghu Kuvempunagar · Jun 5, 2021

NedL said:
Thank you for posting this, it's very interesting.
My paper developer is loaded with bromide ( since I use it replenished )... but might give it a try anyway to see what happens.

Please do let me know what results you get, I would be interested. BTW with paper there's another possibility which I have not tried myself, but you might be interested - print out after the sensitization bath. This might work out better than printing out without sensitization.

Raghu Kuvempunagar · Oct 22, 2021

[Update 22nd Oct, 2021]: Recently I revisited this topic and I did two tests. First, I used the Thiourea nucleation idea in paper reversal. Previously, I had used it only for film reversal. Now I can confirm from my own experience that it works perfectly in paper reversal process as well. The results have a sepia-like tone, but since this is silver, it can be bleached and redeveloped/retoned.

The second test I did was using Thiourea Dioxide aka Formamidine Sulphinic Acid (FSA) in place of Thiourea for making the nucleating bath. It also works fine in film reversal giving warm tone slides. I will give it a try in paper reversal in the coming days.

Sodium Dithionite is another option for the nucleating bath. But as it doesn't keep well in aqueous media, it needs to be mixed fresh every time.

mohmad khatab · Oct 28, 2021

Raghu Kuvempunagar said:
[Update 22nd Oct, 2021]: Recently I revisited this topic and I did two tests. First, I used the Thiourea nucleation idea in paper reversal. Previously, I had used it only for film reversal. Now I can confirm from my own experience that it works perfectly in paper reversal process as well. The results have a sepia-like tone, but since this is silver, it can be bleached and redeveloped/retoned.

The second test I did was using Thiourea Dioxide aka Formamidine Sulphinic Acid (FSA) in place of Thiourea for making the nucleating bath. It also works fine in film reversal giving warm tone slides. I will give it a try in paper reversal in the coming days.

Sodium Dithionite is another option for the nucleating bath. But as it doesn't keep well in aqueous media, it needs to be mixed fresh every time.

What is pH?
The acetic acid available to me is at a concentration of 70% only, and I also have sulfuric acid 90%..
What do I do
I hope you can show us some of these results if you don't mind.
I'm using Fuji's formula, but it needs a lot of patience and accuracy during preparation and I really feel tired after gritizing it,,
So I might consider trying that simple formula of thiourea, why not

Raghu Kuvempunagar · Oct 28, 2021

mohmad khatab said:
So I might consider trying that simple formula of thiourea, why not

What is proposed is an alternative to light fogging in B&W reversal processing. Since you prefer light fogging, the proposed method might not be very useful to you.

If what you have is 70% Acetic Acid, use about 55ml.

mohmad khatab · Oct 29, 2021

Raghu Kuvempunagar said:
What is proposed is an alternative to light fogging in B&W reversal processing. Since you prefer light fogging, the proposed method might not be very useful to you.

If what you have is 70% Acetic Acid, use about 55ml.

Thank you my dear, God bless you.

The Black Pharaoh · May 30, 2023

Hi Raghu!

Really cool article. I've been using TBAB as my fogging agent for colour reversal. This is what Kodak E-4 used before tin chloride.
I am wondering if Thiourea would work with colour?

I don't understand what "nucleating" means. i'm guessing this is a separate bath for reversal?

Thank you.

B&W Reversal Processing: fogging/nucleating agent for second development

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