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Thread: Chemistry Query: grain enalrgement from potassium ferricyanide or bromide?

  1. #1

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    Chemistry Query: grain enalrgement from potassium ferricyanide or bromide?

    I find David Kachel's SLIMT technique useful for handling long subject luminance ranges. For those not familiar, it is a means of using highly dilute potassium ferricyanide between exposure and development to hold back density in the most exposed parts of a negative or print. (Details are provided on his website; just search for his name, and then for SLIMT on his home page's search function.) One thing I noticed when retesting/"calibrating" it a couple of years ago, was that in smaller formats (35, 645), the grain in the high values became a bit less distinct and resulting enlargements slightly less sharp with SLIMT processing than without. I should mention, I use D-23 developer. I was comparing N- contractions between D-23 1:1 with SLIMT and D-23 at 1:3 without. SLIMT processing does a superior job of holding shadow detail, while the 1:3 dilution yields an exquisite highlight detail.

    I asked Mr. Kachel about it, but he had not noticed this effect, probably because his work is large format. I am just curious as to whether someone here might know why either potassium ferricyanide or potassium bromide, or their combination, even in the extreme dilutions used in SLIMT (around 1:1000) might cause this. For my work -- mostly portraiture -- the issue is not crucial. I'm just curious.
    Philip U.

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
    https://www.flickr.com/photos/156933346@N07/

  2. #2

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    Re: Chemistry Query: grain enalrgement from potassium ferricyanide or bromide?

    Ulophot,

    I imagine that what you are seeing is the silver-solvent effect from the D-23 developer used 1:1. At that dilution, the amount of sodium sulfite (about 100g/l if I recall) acts as a silver solvent, softening the grain by dissolving some of it from the edges of the grain. This results in "softer" grain but less acutance (sharpness). Using the developer at higher dilutions reduces the sulfite concentration and the solvent effect is reduced, resulting in more pronounced grain and more sharpness. Kodak states this clearly in the directions for D-76, a close relative of D-23.

    In other words, the issue is likely not related to the use of SLIMT at all.

    FWIW, I use SLIMT as well for contractions and have not noticed this effect. I, too, shoot large format. Still it is hard to believe that the grain is not affected at all by SLIMTs, just that the effect is not noticeable usually.

    To check whether what you are seeing is due to the SLIMT or the developer, do a test with and without SLIMT using the same developer dilution and then compare negatives. That will eliminate all the variables except one.

    Best,

    Doremus

  3. #3

    Join Date
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    Re: Chemistry Query: grain enalrgement from potassium ferricyanide or bromide?

    Thanks, Doremus. I'll run a test soon and post back.
    Philip U.

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
    https://www.flickr.com/photos/156933346@N07/

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