Seeking clarification of the Reversal Process

Hi,

I'm trying to get a better grasp of what's going on chemically with the B&W reversal process. I'm coming at this from a DIY 16mm work flow. I've successfully processed many times but am still having a few difficulties with the descriptions I've studied. I hope some of you knowledgeable folk on this forum can set me straight.
Let me spell out my understanding and I'll raise the gaps in knowledge where they appear.

1. In camera exposure + 1st developer
Where light hit the film the Silver Halide turns to Metalic Silver (which is black).
I'm assuming here that less intense light means less dense areas of silver. (Correct me if I'm wrong)
My main question here is what effect (if any) does the developer have on the Silver Halide that hasn't been exposed to any light? Is there any solvent action on the unexposed areas? (I'm assuming no is that correct?)

2. Bleach
Bleach now removes the Metalic Silver. Would it be correct to say that where light hit the film, this area has now (after application of the bleach) become positive?

3. Re-exposure
Exposes all the silver halide that was not exposed in the camera.

4. 2nd Developer
All the now exposed Silver Halide is converted to Metalic Silver (now black on the Neg)

5. Fixer
Removes any undeveloped Silver Halide
Is that all the Fixer does?
And if I've done the 2nd developer long enough there should be very little undeveloped Silver Halide no?

Thanks in advance

Bleach removed the metallic silver and left the unexposed undeveloped silver halide alone.
The silver halide is not opaque yet, but exists in positive proportion to the corresponding negative silver image which was removed by the bleach.
Then you expose all the silver halide and develop it all. Fixer, yes it would remove any undeveloped silver halide which the second developer may have not gotten to by the time you finish.

First of all, welcome to APUG (Photrio)! Glad you are here; it's nice to have another movie film shooter (there aren't too many of us!)

1.

Oulipo said:

My main question here is what effect (if any) does the developer have on the Silver Halide that hasn't been exposed to any light? Is there any solvent action on the unexposed areas?

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With the exception of D-88, most reversal developers contain significant amounts of silver halide solvents (sulfite, thiocyanate, thiosulfate), and so AgX will be solubilized to some extent. The solubilizing action is particularly necessary to clear the film in highlight areas by promoting physical development, but there will of course be some degree of solvent action in the unexposed areas as well.

2. When you view the film after the bleach bath, the area where the light has hit the film will be clear, and the as of yet unexposed area of the film will be the milky colour of silver halides. You will be able to make out a faint positive image. The emulsion will likely by coloured by the bleach, and different emulsions may have different colours, even in the same bleach.

3. Yep.

3.5. I strongly recommend using a clearing bath (either 1% sodium sulphite for dichromate bleach or 5% sodium bisulphite for permanganate bleach). This will help to prevent chromium/manganese insoluble deposits (i.e. stain) in the film and will also etch the surface of the grains, making them more sensitive to the re-exposure step.

4. Pretty much all the AgX, but not entirely. There are some insensitive and/or less develop-able (i.e. inert) silver halide grains which will not be developed under normal conditions. If you really wanted to, you could use a fogging developer or other strong reducing agent like a sulphide toner, and you would fully reduce all the silver halides. But I would argue against this practice, since this can lead to a high Dmin (fog visible in the highlights.) For example, when I sepia tone my reversal slides, I always follow the steps to the end (i.e. re-expose (3), develop (4), fix (5)) before rehal-bleach and toner, even though you could certainly dunk the film in sodium sulphide immediately following step (2).

5.

Oulipo said:

there should be very little undeveloped Silver Halide no?

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Yes, there is very little undeveloped silver halide, but as mentioned above, there are some inert grains which will not be developed with a "normal" developer. These grains could lead to discoloured highlights in the future. Also, if there are any silver or chromium/manganese deposits in the film left over from bleaching, fixing may help to remove them.

My sources for the above are my personal experience (mainly regular 8mm and medium format stereo slides) and Grant Haist's book "Modern Photographic Processing Vol. 2". All the best with your efforts. I have found reversal processing to be highly rewarding.
Ian

Thank you Bill and Ian. That's very helpful. I'm slowly getting my head around this. Interesting what you said about the Clearing Bath. I do use a clearing bath but didn't include in my description as I thought it was just a beefed up wash to clear the remaining bleach.

You’re welcome Oulipo, and thanks Ian for adding details from experience! I haven’t done any reversal processing in a long time. I used to occasionally make slides from Panatomic-X. I shot the normally ASA 32 film at EI 80. Since that would leave more undeveloped silver halides in the highlight I see the importance of solvent action in the developer(s).