Since I settled on D23 as my sole developer some months back, I have run a series of tests, focusing on handling extended luminance ranges. My interest is location portraiture, in 4x5 and 645, and I want to be able to manage, for example, a subject in a light or white shirt with direct light falling on it—though not necessarily on the face, as in a possible window light setting—as easily as I might a setting requiring N+2. I hope you'll find my results useful as a starting point using D23.
I tested D23 1:3, DD23, and David Kachel's SLIMT contrast-wise bleach technique (http://www.davidkachel.com/assets/cont_pt3.htm), which involves pre-development bleaching with an extremely dilute solution. My results put the latter appreciably ahead of both the others in maintaining low-value density and contrast, just as Mr. K advertised, and I would recommend it to anyone so inclined. It also offers the advantage over DD23 that agitation may be continuous throughout the process—great for those of us who use rotary processing as well as tray. The bleach stocks last indefinitely, and you'll have to do a lot of processing to use them up, because you'll not likely use more than 10ml from each liter in a developing session.
My standard is D23 1:1 for most development. The SLIMT technique will (for now at least) be saved for situations like that indicated above, which may land a white shirt on Zone XI with the face placed on VI. I shoot only HP5+, usually at EI 200 unless the luminance range is very low. I tested SLIMT both in tray and daylight rotary tank.
I found a presoak practical, though I don’t use one for standard development. I used 1 minute. Without it, the effect of the bleach is considerable at typical dilutions and times of 3-5 minutes. The presoak offered better control.
For my tests, aiming to bring Zone XI to about VIII, I found that 50-60ml per liter of water—what Kachel calls working solution (which is diluted from working stock, which is a very dilute solution of two stocks made, respectively, directly from potassium ferricyanide and potassium bromide)—worked well with bleaching of 5 minutes followed by my Normal development. 60ml/liter made perhaps a ½-zone difference compared with 50ml. Reducing my development time by about 8 percent reduced the highest densities another ½ zone.
For a significantly greater contraction, I used 75ml/liter for 5 minutes, followed by development reduced by about 12 percent. That reduced XI to about VII—too much for most situations. I had also tried 100ml/liter; too much for the results I wanted. On the other hand, 25-30ml/liter for 3 or 5 minutes, followed by Normal development, would suffice bring Zone IX to VIII. I did not pursue this beyond an initial test, because I was seeking greater contractions. N-1 I handle with reduced development alone.
Think through the containers or trays you'll need for the batch size you'll require. Paterson makes a good 45ml graduate. For the rotary tank, I found it simplest to have at least presoak, bleach working solution, and developer all lined up. The working stock was already taking up another graduate. Having stop and fix ready also would be nice, but I had plenty of time during development to rinse and recycle my graduates.
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