IIRC a ferricyanide bleach is a rehalogenating bleach. This would turn your developed paper negative back into an unexposed piece of paper, which after exposure to room light would quickly turn solid black. The dichromate and permanganate bleaches remove the developed silver, leaving the remaining silver halides behind. The reexposure to light gets you a developable positive image.
Thanks for sharing the details; I need to try this someday.
Originally Posted by SMBooth
it seems that about halfway to developing out the image (30-40 seconds) if i just hit the bathroom lights for a split second (halogen, not bad), or hit it with a high power xenon strobe (much better).
Originally Posted by holmburgers
i really have had very inconsistent results so far. unfortunately i burnt the bulb on the higher watt strobe unit i was using (24W bulb), and trying to get the paper to reverse with a vastly smaller bulb is not working at all. i haven't put any time into more exposures with the bathroom light, although that's what i was working with at first.
i think this process has a lot of potential for producing some very very interesting pictures, as unique and unreproducible direct images.
okay, took some time this morning to revisit the process!
here's my setup in my bathroom:
i've obviously got my camera, homemade softbox (on a really wimpy Pentax AF160 i got for free, supported by a rubik's cube on top of the focusing screen), single halogen light source, 1:8(ish?) ilford multigrade developer, a water bath for stopping and washing, and rapid fix.
the whole approach is very imprecise, because i'm dealing with expired paper and didn't want to get my phone to use as a timer while i was in there banging the portraits out. i metered the bathroom light at EV 3.5 for EI 12 (which i estimated a full stop slower for the paper, roughly--so more like a true EV 1.75 for EI 6) with my handy little incident meter, and the softbox i'm eyeballing off the exposure chart on the back as a half-stop under normal ( EI 25 @ f8, 1m = EI 6 @ f2.8, <1m + power reduction from diffuser). the flash exposure came out fairly close to true, though a little under. however the mostly-flash exposure (shortest shutter-open time) came out the nicest.
the procedure for each was to expose, fog the plate a touch with light through the crack at the bottom of the door (~1 s), develop to completion in darkness (~1 min), flash the bathroom light to initiate reversal (0.3 - 0.1s, you get a good look at the negative at this point), develop to completion (~50 s), put in water stop bath for ~10s letting the developer work its way out (and at this point your eyes have well adjusted again and can clearly see your plate has darkened), fix for whatever feels comfortable and wash in the sink for a couple minutes.
these are the fruits of my efforts today, arranged top to bottom, right to left. the first was a gross underexposure (i had accidentally left the stop at f8). the second shot was as lit as i could possibly get it for ~4s exposure and the flash, and reversed with ~0.25s of bathroom light--it came out with badly blown highlights on my nose and forehead that did not reverse. i believe that this unwillingness of fully developed halides to reverse means there are very hard limits on the maximum contrast ratio that can be captured with this process.
the rest of the shots in the right column were experimenting with exposure and flash time. when i do proper scans of these images i'll make a post of my recollected exposure data (whatever that'll mean) in a later post.
the two (i feel) more successful exposures on the left column were the last two, and were a bit different. these exposures were for shorter times, roughly 1.5s, and when flashed with the overhead light showed almost no density at all as a negative image. in fact, for the top image on the left the paper was completely white, i couldn't see any density at all when i flashed it, and agitated it for a good minute and a half in the developer hoping i could get something out of it. the lower image was about the same for exposure and density when i initiated the reversal, and just trusted that i'd see something. obviously they're much lighter in tone, but i'm happier with them as there are very little to no unreversed highlights. i believe this is a factor of both shorter exposure times to avoid blowing highlights on the front end, and more gentle reversing exposures.
here're some scans of the photographs I made yesterday, all calibrated to maximize the scanner's range and replicate the relative tonal characteristics of each image. i scanned in color because there are slight hue differences with different exposure levels. i have not manipulated these images at all to make them comparable, but the actual photos have a characteristic gray-brown hue to them, rather than the blue or green color these scans show.
first, a little more technical information about the procedure. i placed myself in the focal plane, which i established with a no. 2 diopter and racking the bellows in all the way at wide open (Sekor 80mm f 2.8 blue dot). camera is loaded with lightly flashed paper, lights on, expose, lights off, develop to completion (1 min), flash for reversal, develop to completion (+water bath soak to a stop), fix, lights on and figure out what to do for the next one. as above, i metered the bathroom light at EV 3.5 for EI 12 and eye-balled exposure from there.
the first image was an overall failure. the following (second) plate was made with a 5s exposure with the flash. reversal exposure was roughly 0.2s. obviously blown highlights on my nose and forehead retained their density in the reversal process, and average density was high with a low contrast.
this next plate was exposed for about 3.5s with the flash and the door open (with light from my room lights and outside through the window). the reversing flash was a touch longer, about 0.25s. nice high density on the frame edge, and shadows, less held-over black blown out highlights, although the overall contrast is ridiculous and detail is only on my ear and neck where the exposure was lower.
this plate had an exposure of 3s with the door closed, and the flash. the reversing exposure was about 0.25s. better detail, no blown highlights, but again low contrast and higher average density.
this plate had an exposure of 6s, without the flash (didn't fire the first time so did a double exposure). reversing exposure was much shorter, about 0.1s. terrible blowing of highlights again. however, i was encouraged by the very high overall contrast generated by the short reversing exposure.
this plate was essentially all bulb, ~1.5s exposure. reversing exposure was at first 0.1s, but i saw the negative showed no perceptible density after a full minute of development. after a few seconds of development in the dark and not seeing any color change i flashed again for 0.1s, and developed for a full minute and let it rest in the water bath hoping something would come out. great tonal range, detail, lower average density, better overall contrast. this is my favourite photo, basically an accident (but a happy one).
this plate was ~2s exposure with flash, and a 0.1s reversing exposure (maybe shorter). i trusted that the nearly-zero observed negative density would produce a positive image, and produced a high contrast, low maximum density image. there is a black mark in my left eye (remember, rotated inverse images) from a blown unreversed highlight. as a side note, i'd ripped the corner off to test my developer that had been sitting in the tray at the start of the day to see if it was good having been mixed a couple days before (it wasn't, so i started this series of photos with fresh).
this was my most successful image from my first experiements with this approach, and was produced essentially by accident. scanned with the same scanner, same settings, for comparison. exposure for this image was with my flash (bare) held at arm's length, shot twice, ~20s exposure in lower incident light only through my bedroom window. reversing exposure roughly 0.2 seconds (i'm guessing, this was a month ago).
so it seems to me that there is a LOT of leeway for producing a recognizable photograph, but definitely needs dialing in to get good repeatable results. flatter, even lighting seems to have the ability to produce good detail and appealing contrast. from my experiments it seems that the strength of the latent image is less important than the duration of the reversing exposure--longer secondary exposure can compound with long initial exposures and solarize the crap out of your image. good, healthy developer seems to help the process along to generate good positive density, but definitely hurts tonality with fogged highlights and lower contrast.
this information is all but useless, and is really just a place to start for anyone else interested in experimenting. i'm sure you'll all pay closer attention to what you're doing than i have. :)
i cut more paper just yesteryday, now trying it with some highly expired Kodak Multigrade II RC. it seems much slower than the Ilfospeed 3 my previous images were made with.
also, i (actually!) measured my developer concentration, and played with the process there. my estimations on concentration were way off, a triple strength dilution (1:3 rather than 1:9 as per bottle instructions for Ilford Multigrade) is required for the image reversal to occur. strong-but-close-to-normal concentrations resulted only in an off-color fog when the secondary exposure was applied.
i'll post more results soon.
I tried this out some time ago, mostly just to see if I could make it work. I exposed the paper to a negative in the enlarger, and then reversed it, so I had a negative to negative process. It's pretty cool to do, and it would be a good pairing with a pinhole camera. I never could get fiber based paper to work without some staining. I guess that seems rather obvious but until you try it you never know for sure.
Not to me, Why?
Originally Posted by erikg
I was going to try FB paper.
yeah i doubt the emulsion support has a huge effect on how it will respond to the process, but i've found huge differences in behavior between the Ilfospeed and Multigrade II. definitely different papers are going to respond very differently, not to mention developer combinations.
anyone have a good idea for how to make a rudimentary 6x6 step tablet? i'd really like to begin taking this process halfway seriously.
Andy, does your 6x6 camera have a darkslide per chance (like on a Hasselblad film back for instance)? If so, you could pull it out in increments, giving a -5 exposure on a white/gray ground each time you pull it out. If you can pull it out 11 times in the length of 6cm, dividing the film into 11 sections, the first exposed portion will eventually get +5 exposure and the intermediate sections will get +4, +3, +2, +1, 0, -1, -2, -3, -4, -5.
You could do the same thing under an enlarger, but it'd just be a bit trickier.