Non staining print reducer

[larfe]

Hi APUG,

I've been experimenting with making very dark prints and bleaching selectively the life out of them to give them a special look.
Unfortunately this results in staining 8 times out of 10 with either ferri on it's own or if I use it as farmer's reducer.

There is a formula similar to farmer's in the darkroom cookbook but with thiourea added which supposedly does not stain but I wanted to find out what people think of this in any case.

Thank you

 

[Gerald C Koch]

Thiourea is used as a brown toner and not as a bleach. I think you have misread something. If you are experiencing staining with any ferricyanide bleach then probably they will all give similar results. Try a persulfate bleach like Kodak R-15 there should be a formula in the cookbook.

 

[Rudeofus]

Thiourea is not only a compound which releases Sulfide in alkaline environment, it also is a strong silver complexing agent, i.e. fixer. In this second function it is used in both Rowland Mowrey's Superfix I, and in some experimental Ilfochrome dye bleaches. As long as it is kept neutral to acidic, it will not stain, and it appears to be more resistant to oxidation than Thiosulfate.

@larfe: when I rehal bleach prints of mine, there is always a strong brown residue, which does not go away with fixing. Nobody could so far explain to me what this is, it may well be Silver Sulfide, but I really don't know. There is a good chance that bleaching in your case reveals some this brown residue, creating an overall brown image tone.

 

[larfe]

Interesting

@Rudeofus: you mean when stick your print in a rehal bleach to completion? Indeed there is always this brown faint image

 

[Gerald C Koch]

Thiourea is not only a compound which releases Sulfide in alkaline environment, it also is a strong silver complexing agent, i.e. fixer. In this second function it is used in both Rowland Mowrey's Superfix I, and in some experimental Ilfochrome dye bleaches. As long as it is kept neutral to acidic, it will not stain, and it appears to be more resistant to oxidation than Thiosulfate.

@larfe: when I rehal bleach prints of mine, there is always a strong brown residue, which does not go away with fixing. Nobody could so far explain to me what this is, it may well be Silver Sulfide, but I really don't know. There is a good chance that bleaching in your case reveals some this brown residue, creating an overall brown image tone.

I have seen this staining too which is why I no longer attempt to bleach printts.

 

[Rudeofus]

@Rudeofus: you mean when stick your print in a rehal bleach to completion? Indeed there is always this brown faint image

Yes, this is the brown image I described. One day I'll find out what it is and why it is there.

I have seen this staining too which is why I no longer attempt to bleach printts.

The strange thing about this brown image is that:

1. Ferricyanide has been called "the perfect bleaching compound for photographic products"
2. C-41 and E-6 have to use much weaker bleaching agents, yet get rid of all the silver on film.

 

[pentaxuser]

I have yet to try bleaching but I cannot recall in any books or previous posts about bleaching, seeing any indications that bleaching produces this brown image.

If there had been a warning that this might happen I think I'd have remembered it. Warnings are usually the things that you remembers even if you forget some of the rest you read

pentaxuser

 

[larfe]

Well, the thiourea does nothing to prevent this 'staining' or the appearance of that brown image.

I've emailed Tim Rudman in a move of desperation...

 

[Rudeofus]

I have yet to try bleaching but I cannot recall in any books or previous posts about bleaching, seeing any indications that bleaching produces this brown image.

If there had been a warning that this might happen I think I'd have remembered it. Warnings are usually the things that you remembers even if you forget some of the rest you read

This reference provides not only a decade old reference to yellow/brown stains from bleaching, it also suggests a solution at the end of the thread. I have not tried this, but I am very curious whether it works.

 

[benjiboy]

Potassium ferricyanide goes green after a while, Potassium cyanide bleaches prints without staining, but it's very difficult to obtain, even more difficult to dispose of after use..

 

[larfe]

This reference provides not only a decade old reference to yellow/brown stains from bleaching, it also suggests a solution at the end of the thread. I have not tried this, but I am very curious whether it works.

OK well thanks for the link. I've just tried the 10% thiourea + 5% citric and and and.... IT WORKS IT WOOOOOOOORKS oh boy oh boy oh boy

 

[larfe]

Now if someone could explain why!