If you are experienced with Selective Latent Image Manipulation Techniques and are interested in doing a small research project, here are the details...
In going through my now well-yellowed notes from my original SLIMT research I noticed one area I had intended to look into and never did. As I no longer have a conventional darkroom I will not be pursuing this myself. (For those who don't know, I am the inventor of all SLIMT techniques and a few others.) This is a relatively promising area and should be easy to investigate.
It has to do with two basic fundamentals of the behavior of photographic materials:
1. Developers and photographic materials have what are called "induction times". For example, the length of time that elapses between immersing film into developer and the moment the first silver halide crystal develops is the induction time for that developer/film combination. Development does not begin instantly. Also, and very important, the more exposure a silver halide crystal has received, the shorter the induction time for that individual crystal. This is the reason highlights begin development long before shadows and is also the reason that as you reduce development time to compensate for a subject with a long reflectance range you also lose film speed: lesser exposed areas don’t develop at all because they don't reach their induction times before development is halted.
2. Developers are not the only photographic solutions that have induction times. Fixers and other chemicals do also. This is the reason monobaths (developer and fixer in the same solution) can work. If correctly formulated the induction time for the developer in a monobath is much shorter than that for the fixer and therefore development is complete before the fixer can begin to work.
Potassium ferricyanide, the bleach used in most SLIMTs, also has an induction time. In addition, most all film developers contain potassium bromide, the other essential ingredient for SLIMTs for film (SLIMTs for paper do not need it). Therefore, adding potassium ferricyanide directly to film developer has the potential, if the formula is correctly balanced, of performing both the latent image bleaching AND film development at one and the same time.
This single bath process would have the likely benefit of being more predictable and consistent. It would also likely provide inherently more even development (the single bath concept, like conventional monobaths, tends naturally toward more even development). SLIMTs are already consistent and predictable and development also is even, but more is always better. Conventional SLIMT concentrations are so minute that small errors in formulation can potentially produce noticeable errors in final density range. This potential should be reduced by a single bath as induction time for the developer would tend to play a significant role in stopping bleaching.
If doing this myself I would start with a weakened developer (probably about 50% of normal strength) and a stout (far higher than normal SLIMTs) potassium ferricyanide concentration, two identically exposed negatives, one developed identically in the same developer but without bleach. This would be a 'proof of concept' test. The point is to see if it is possible for the bleach to have a shorter induction time than the developer. If the negative developed with bleach in the developer shows any tendency to be usefully flatter, or even if it is blank, this would largely prove the technique is viable and only needs to be refined.
There it is. I have been sitting on this potentially useful SLIMT for about a decade. If you are interested, feel free to take off and run with it. If you can make it work, write an article, teach workshops, sell it to Microsoft for a million dollars... well, maybe not that last one. Just be kind enough to give credit where credit is due. And please apprise me of your results.
David Kachel
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Originally Posted by Nathan Potter
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