Bleach bypass as speed enhancement?

Once, back in the early oughties, I processed a roll of T400CN with bleach bypass -- color developer, stop bath, and straight into C-41 fixer. At that time, I exposed the film for EI800, in the expectation that the retained silver would add about one stop of density in the entire image.

Now I have XP2 Super on hand, and I'm interested in continuing that experiment. This is a film with a reputation of pushing and pulling well anyway, and because it's black and white even in dye image processing, there's no color effect -- and it's known to give excellent results in B&W developers, as well as in C-41.

It's obvious that retaining the silver image in addition to the dye cloud image will increase density, hence effective film speed -- but the question is, how much? My plan was to shoot and process a partial roll of 35mm, bracketed from box speed up to about -3 stops exposure (EI 3200) and process normally (3:15 at 102F in C-41 color developer) with bleach bypass, but I can save this step if someone can tell me they've done this and what the effective speed was.

If no one has definite knowledge, then I'll do it myself and report the results, so we'll all know one more way to get the most out of XP2 Super.

Hi, I've never tried it, but in principle I'd expect the result to be very much like making a b&w film mask after the fact, and sandwich it with the original neg. In essence it would seem to mainly increase contrast, almost like push processing. But this is just a guess, and in my experience, carrying out the actual experiment sometimes reveals an unexpected angle.

Another idea you might try is multiple developments of the dye image. In principle, if you were to do the bleach bypass, but do fix, it seems like you should then be able to rebleach the silver image, converting back to silver bromide. So presumably it can then be exposed and developed (in color developer) again, forming another dye image. And on and on. But I fear it will just be driving up the contrast.

Best of luck.

Ps, it occurs to me that, assuming successive color developments actually work, that it may be useful to use highly diluted developer so as to act as a compensating developer, holding the contrast in check. Again a complete guess, but it seems as though it might work.

Pps, given the extent of your tech knowledge I'm guessing that you are already familiar with the effect of "flashing" film to improve shadow detail. If not, the point is that we get what one might call a sub-latent image that is there, but not quite strong enough to be developed. But by giving a very weak additional exposure, an overall "fog," some of the sub-latent images can be upgraded to "latent," thus becoming capable of being developed. A useful exposure might be 3 to 4 stops under a metered exposure, so an out-of-focus double exposure of a blank wall, or whatever, could do it. If you overdo it you can get a bothersome "flat" look in the shadow areas, so the effect is limited. (The effect should be identical to flare light, which is sometimes demonstrated on sensitometric curves; one can see how the limitations play out.)

I hope you go ahead and do it Donald. it will be interesting at least and may have a serious practical side as well for all of us

pentaxuser

I agree, I'll mostly be getting higher contrast, but even the shadow values should be pushed up about one stop (at least those that retain some detail, perhaps Zones I and II). Tempting to suggest bleaching and redeveloping in a known compensating B&W developer (Moersch, for instance, or pyrocat) would control the highlights enough to avoid the "push" high contrast look.

And yes, I'm aware of preflashing, though IMO it's more useful as a form of "burning without burning" in printing than on the negative. If I screw up a preflash on my paper, I can just pull another sheet out of the safe; screw it up on film, and I won't even know until I'm back in my darkroom and see that my developed negatives have no actual clear highlights at all, just a drab gray.

That said, the way I recall Ansel describing preflashing, the exposure used should be just about equal to Zone I -- but that's determined by the film's (tested) real speed, not by the scene.