reversal 2nd dev fog
I have gone through great pains verifying no fog on the first step, developing unexposed film.
During the light flash step, I have visably verified the leaders (35mm) are indeed clear.
However after the 2nd dev step (and fix) the film comes out with fog on the leaders.
The developer I use is Dektol, the bleach is Potassium dichromate, the clear is sodium metabisulfite.
Is the bleach or clear step not long enough? I understand that I may not see some of the emulsion left on the leader after the flash step, but am I just missing something?
You don't say whether the amount of fog you are seeing after the 2nd developer is objectionable or not. Upon projection are the results unsatisfactory? I say this because you are using both a film and a developer for purposes for which they were not designed. Perfect results may not be possible. When the company dr5 was doing reversal processing certain films were not recommended for reversal.
For best results, the amount of silver halide solvent in the first developer must be carefully adjusted for each type of film you are reversing. Sodium thiosulfate does not work as well as potassium thiocyanate to clear the highlights. Developers specifically designed for BW reversal processing use thiocyanate rather then thiosulfate.
Have you tried using a chemical foggant rather than re-exposure to light? While it is hard to have too much re-exposure it is possible. A simple 2nd developer using sodium sulfide will act as a fogging developer. You might get better results with chemical fogging.
The amount of fog was more of a surprise than anything else, due to it not existing for the developer bleach/fix. It is my understanding that there should be no silver left to develop on the leaders at the 2nd dev stage.
I have working processes, even for the film at hand (TMY here). What I have been doing is working out a more systematic approach, attempting to get the most out of any film. To do that I need to be able to explain any surprises along the way, with work around to suit.
I did not mention the amount of silver solvent or the film as they were not important or required to answer the question. I am looking for a more generic answer.
I would think I would still get fog using a chemical foggant vs exposing to light. Developer can only develop the active silver that remains. It's my observation that it should not have existed.
Originally Posted by Gerald C Koch
Is it possible for the second developer to leave behind a fog, even if there is no silver present?
It would be interesting to see if what you are seeing as fog in the leader is actually silver. You could use Farmer's reducer and refixing on a portion of the leader and see whether the fog goes away. Treat half the leader with the reducer and leave the other portion untouched. So years ago Ilford had a system for reversing their films which used a permanganate bleach. Some people were experiencing what they thought was fog but which was actually manganese dioxide precipitaated in the emulsion. This was caused by an improperly compounded bleach. The bleach must be sufficiently acidic to prevent precipitation of either manganese dioxide or chromium oxide in the emulsion due to carryover of developer. Do you use a rinse between the first developer and the bleach?
Here are the instructions for Ilford's process http://www.ilfordphoto.com/Webfiles/20061291034093.pdf
I don't have any Farmers Reducer and it would be interesting to try, if I can pick some up locally. I will look tomorrow.
I swallowed up that reference (and others) to the ilford pdf long ago. It's one of the reasons I am doing what I am. It wasn't methodical in its approach and just gave 1 or 2 unique examples. It didn't take modern emulsions into consideration or if you wanted to use....fuji....foma....lucky.....etc
Dr5 is living proof that a systematic approach is possible. They have it all worked out; pushing, pulling and the like. When I demystify all that I can, I will try to make some sort of newer reference. Something a lot clearer and relevant than is currently available. Which brings me back to the question at hand; arggggg fog...
I think your problem is the clearing step. Common practice is to follow dichromate bleaches with sodium sulfite; permanganate bleaches go with the metabisulfite.
That's what stood out to me at least.
I don't believe I did that.....
Don't believe you followed with sulfite?
Let us know if that clears up the problem. (did you catch that pun?... yuk yuk yuk :joyful:)
My guess would be incomplete first developing or incomplete bleaching. The first developer has to convert all the exposed silver halide in the very-well-exposed leader to metallic silver. The bleach has to remove all of the 'black' silver, leaving just the undeveloped white silver halide in the emulsion.
I've done my reversal work using sheet film and I turn on the room lights when the film enters the bleach. This way I can make sure the bleaching has finished and it also insures complete 2nd exposure. Bleaching can take much longer on heavily exposed film - like the leader - than it can on regular negatives (er, positives). Film can appear clear in the bleach even though there is quite a bit of residual silver halide in the emulsion - if you look at the negatives after the bleach step it looks like they are quite devoid of all highlight detail, but the detail re-appears in the 2nd developer.
Another mechanism may be that the heavily exposed leader is partially solarized - exposed so much that it is reversing a little bit all on it's own - something that would never be noticed in regular processing. Try giving a frame a Zone XII exposure - enough to be completely clear, but well below any self-solarizing threshold. If this frame comes out clear, without fog, then I would not pay an more attention to leader density.