Odd theoretical question

[htmlguru4242]

I was thinking the other day; I have some sheet film that I accidentally exposed to room light. It's nothing important, and I was going to throw it away, but I realized something.

If I were to develop the film so as to render it completely black, could I put it an a re-halogenating bleach and re-develop it to get images on it? I realize that the characteristics of the film would be changed, but would this work at all?

 

[pgomena]

Theoretically, yes. You probably will lose all the antihalation backing and sensitizing dyes in the process, leaving you with a blue-only sensitive emulsion. Speed likewise may be affected.

Peter Gomena

 

[htmlguru4242]

Hmm, i figured that't I'd loose some of those, Peter, but i'm not sure.

has anyone tried this?

 

[Jim Noel]

It would be fun to try, and we might all learn something from your experiment.
Jim

 

[htmlguru4242]

I'm going to try this. I just realized thoguh, I had some rehalogenating bleach that I made up awhile back, but damned if I remember the formula. Right now, I have some dichromate / sulfuric acid bleach that's prepared.

How would I convert this to rehalogenating?

 

[jim appleyard]

Theoretically, yes. You probably will lose all the antihalation backing and sensitizing dyes in the process, leaving you with a blue-only sensitive emulsion. Speed likewise may be affected.

Peter Gomena

That sounds good to me. You might get an "aura" around images, something like what you get with IR film?

Go, what have you got to lose? Ler us know what you get!

 

[pgomena]

Yep, you've nothing to lose. Might as well try it. You'll need to wash thoroughly after using the bleach. Have fun!

Peter Gomena

 

[htmlguru4242]

I'll try this this weekend

 

[Kirk Keyes]

That sounds good to me. You might get an "aura" around images, something like what you get with IR film?

But it will probably have ortho sensitivity as you may was out the sensitizing dyes. And the film speed will probably be greatly reduced.

I'm sure PE could tell us all the things to watch for here.

 

[gainer]

You probably want a ferricyanide-bromide bleach. I don't see how the acid dichromate bleach would convert silver into silver bromide. The bleach you find in formularies for sepia toning with sulfide should work. Be sure you do it in the dark or under a deep red safelight. Don't let sulfide near it!

 

[Gerald Koch]

If the original emulsion was a iodobromide one then the iodide portion would also be lost when the rehalogenating bleach is used. This would result in further speed loss.

 

[htmlguru4242]

Good point, Gerald.

Why not add an iodide to the bleach?

PE, any comments here?

 

[Ian Grant]

Wrong Dichromate bleach.

LA Mannheim recommended the following for restoring fogged paper and film:

Potassium Bichromate 8.3 gms
Hydrocloric Acid 25 gms
Water to 1 Litre

or

Chromic acid 6.2 gms
Potassium Bromide 12.5 gms
Water to 1 litre

Soak for 5 mins in either - thoroughly wash then dry all must be carried out in the dark. Resulting speed will be 1/5th to 1/10th of the original.

Ian

You probably want a ferricyanide-bromide bleach. I don't see how the acid dichromate bleach would convert silver into silver bromide.

 

[Photo Engineer]

Use a ferricyanide bleach with sodium bromide. We call it a rehalogenizing bleach. It forms silver bromide crystals.

You lose virtually all sensitivity and the result will be very very slow and only blue/UV sensitive.

PE

 

[Ian Grant]

The use of a Dichromate halide bleach is supposed to increase the contrast and will result in negatives or film with slightly more density compared to using a fericyanide/bromide bleach.

The dichromate bleach is acting the same as if used for intensification.

Ian

 

[gainer]

Use a ferricyanide bleach with sodium bromide. We call it a rehalogenizing bleach. It forms silver bromide crystals.

You lose virtually all sensitivity and the result will be very very slow and only blue/UV sensitive.

PE

Maybe about like what Fox-Talbot had to contend with?

 

[Photo Engineer]

Maybe about like what Fox-Talbot had to contend with?

I would guess an ISO of about 3 - 6, but that is just a guess, if he is lucky.

PE

 

[Photo Engineer]

The use of a Dichromate halide bleach is supposed to increase the contrast and will result in negatives or film with slightly more density compared to using a fericyanide/bromide bleach.

The dichromate bleach is acting the same as if used for intensification.

Ian

Ian; IDK for sure, but he wants to get a film and high contrast may not be desirable. Usually a film is about 0.6. This is such an iffy proposition that I cannot predict the results.

PE

 

[Ian Grant]

PE you can't but others do

I cannot predict the results.
PE

I have to admit I did try this back in the 70's & using the dichromate bleach gave reasonable results, a ferricyanide/halide blaech was very flat in comparison.

Ian

 

[Photo Engineer]

PE you can't but others do



I have to admit I did try this back in the 70's & using the dichromate bleach gave reasonable results, a ferricyanide/halide blaech was very flat in comparison.

Ian

Ian, all I can say is that we used a rehal bleach with ferricyanide and bromide. I never investigated the reasoning behind it nor the actual results beyond measurment.

The results are probably more developer dependant due to the morphology of the developed silver, but IDK.

Adding iodide to the bleach will have little effect I suspect, as the major portion of the speed comes from the sensitization and crystal growth which are absent here. In addition, the iodide will be in the core of the grain with no ammonia or other solvent to digest the grain and again to grow it.

It works, but it lacks the true control of speed and contrast that you have with precipitation of the grain. This will be more like the albumin process type grain.

PE