The last week or so I have been experimenting with ortho litho film developed using dilute rodinal solutions modified with the addition of borax and sodium ascorbate. I used 400ml H20, 1/8 teaspoon borax, and 1/2 teaspoon sodium ascorbate. (Sorry for the mix of metric and non-metric measurements.) To this I added either 1ml or 2ml Rodinal.
I shot some scenes in the back yard on 4x5 film and developed two sheets together in a batch.
Just based on the look of the negatives and preliminary testing it seems that the 1ml Rodinal solution will give a graded contrast range if I rate the film at an EI of somewhere in the neighborhood of 1/4 to 1/8 and develop the film in the range of 6 minutes at 75 F with continuous agitation in a rotary processor. The 2ml rodinal solution seems just a bit too active. (In fact, 6 minutes of the 1ml solution might even be a bit too much development.)
I haven't tried doing many controlled densitometry measurements yet, but I might eventually.
Anyway, what makes these observations relevant to the present discussion is that 1ml of rodinal is not much developer, being just a fraction of the amount recommended to avoid developer exhaustion. Therefore, it would seem that such a small amount of developer would risk exhaustion, particularly at a Rodinal dilution of 1+400. However, I don't think that exhaustion was taking place. In fact, fully over-exposed film gave a Dmax of something like 2.4 (as I recall) using a densitometer, so I don't think there is any developer starvation going on. I presume that the ascorbate is regenerating the para aminophenol, preventing exhaustion of the developer.
I also think that the ascorbate is probably not operating directly as a developer. From what I have been able to learn by my limited reading, if ascorbate is operating directly as a developer one would expect some fog, but in this case there is essentially no fog. In fact, base plus fog on an unexposed piece of film was something like 0.04 density units. (Yes, I have the decimal point in the right place.) This would argue against direct developer action by the ascorbate.
I eventually hope to follow up with more controlled experiments, but I thought I would mention the results of my preliminary experiments.
Any thoughts on this?