Chemistry Query: grain enalrgement from potassium ferricyanide or bromide?

[Ulophot]

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.

[Doremus Scudder]

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

[Ulophot]

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

[Ulophot]

Testing in progress; initial result suggests that you're correct. Makes sense. Assuming this proves true in my next test, it brings up an interesting possibility, namely, using SLIMT with D-23 1:3 instead of 1:1, in order to capitalize on the improved highlight rendering in fine detail at 1:3, at least for 35mm and 645. During my testing a couple of years ago, I found that SLIMT made a significant improvement over 1:3's maintenance of lower vales, but that was measuring against 1:3 developed for N-2. At N, the speed loss may be less.
I would still reserve it for special cases. As I noted before, my portrait work doesn't generally rely on this aspect. Further, it means 1 roll of 35mm in a 4-reel tank, due to the small amount of Metol at that dilution. But I'm curious to see how it works out.

[Doremus Scudder]

Testing in progress; initial result suggests that you're correct. Makes sense. Assuming this proves true in my next test, it brings up an interesting possibility, namely, using SLIMT with D-23 1:3 instead of 1:1, in order to capitalize on the improved highlight rendering in fine detail at 1:3, at least for 35mm and 645. During my testing a couple of years ago, I found that SLIMT made a significant improvement over 1:3's maintenance of lower vales, but that was measuring against 1:3 developed for N-2. At N, the speed loss may be less.
I would still reserve it for special cases. As I noted before, my portrait work doesn't generally rely on this aspect. Further, it means 1 roll of 35mm in a 4-reel tank, due to the small amount of Metol at that dilution. But I'm curious to see how it works out.

Thinking a bit more about this: Both D-23 and D-76 have 100g of sulfite in the stock (full-strength) solution. Kodak says this about diluting 1+1: "For greater sharpness, but with a slight increase in graininess, you can use a 1:1 dilution of this developer." Since you are already using D-23 1+1, you already have this advantage somewhat. It could be that diluting further to 1+3 reduces the silver solvent effect even more, or it could be that using a weak developer simply adds a compensating effect to the highlights, thereby giving you more "detail" or "improved rendering" or whatever we want to call it. Compensation just proportionally reduces development in the most-dense areas while retaining more local contrast in the middle values. Perhaps that is what is happening, or maybe a combination of the two.

In any case, you may want to try the middle dilution, 1+2 and see if that will give you the highlight rendering you like plus a bit faster developing time and more capacity. However, this mayjust negate the compensating effect.

Happy testing,

Doremus

[Ulophot]

I ran some more tests yesterday, and, although I could hone in a bit more, I think the results are adequate for my purposes. The results are a bit tricky to evaluate, because more than one variable at a time is changing. I could shoot a test target of plain card with thread draped or pulled across it, exposing it for Zone IV and comparing N with N+SLIMT, but I expect that it would just bear out my results so far. After poring over yesterday's results, it seems to me that your comments are more accurate than my perception of SLIMT causing a loss of fine detail rendering. I compared 5x7 prints of sections of 35mm HP5+ negatives enlarged to about 16x20. (HP5 is the only film I currently use, 35 to 4x5, always developed in D-23.)

A comparison of N-2 development in D-23 1:1, with N-2 using SLIMT with N at 1:1 clearly shows increased grain in the latter (6.5 min vs. 9 development), which, combined with SLIMT's support of lower values, removes the distinction of values in details while increaseing the spread of edges in larger areas of high value against low value. A further test, however, restricted the grain increase: I compared N-1 in D-23 1:3 with SLIMT at N 1:3, a developing difference of 12 minutes to 13.5. In this case as well, SLIMT's support of lower values made evaluation of textures tricky, but the difference in grain is negligible and overall, close examination shows the actual rendering of fine detail to be essentially unimpaired.

Thus, for certain kinds of images with relatively low luminance range and medium to high key, and in which fine detail is desired -- for example, fine white lace against other high or medium values, D-23 at 1:3 can be an excellent choice, especially with medium and smaller format film. For supporting low values with N- developments, SLIMT is an excellent performer.

[Doremus Scudder]

Thanks for the info and taking the trouble to test so extensively. It seems, however, that we still can't really blame the SLIMT for affecting the grain size somewhat. If I understand your post correctly, you got increased grain with D-23 1+1 with a negative that was developed for a longer time. The grain increase could simply be due to the longer developing time. To really isolate the issue, one would have to compare values (highlights) of the same density in, e.g., an N-2 negative treated with SLIMT and then developed at the N time and an N negative developed at the N time. Then the time in the developer would be the same for both negatives and comparing equal-density highlights on both negatives would definitely tell the tale.

I still think you are getting some compensating effect with D-23 at the 1+3 dilution, which is helping with the detail in the highlights (i.e., reducing development in the highlights a bit, which, in turn, reduces grain and contrast a bit).

If, indeed, the SLIMT is increasing grain somewhat, it appears to be only slightly. Enlarging 35mm to 16x20 is a 16x enlargement; much greater than I would ever be doing with 4x5-inch film, so the issue for me is practically non-existent.

Best,

Doremus

[Ulophot]

Doremus, thank you for your patience. I failed to write clearly, once again. We agree. What I meant to convey, is that the larger grain in the first instance was undoubtedly due to the nearly 50-percent greater development time, which also combined with SLIMT's low-value support. The negligible grain difference in the second pair effectively confirmed that SLIMT (immersion in which was 5 minutes for all tests, though its dilution was greater for N-1 than N-2) did not contribute to the grain.

The degree of enlargement was simply a matter of seeing the effects clearly. 16x 4x5 would fill a third of my darkroom! My 35mm frames print no larger than about 7.5 x 9.5, even if I crop somewhat; 645 and 4x5 stay on 11x14 paper, with the same caveat. If I were to shoot Delta 100 again, 11x14 with 35mm stays virtually grainless -- beautiful stuff, but I'm on a strict, one-film diet, for now at least, dictated by the speed I need for indoor portraits on 4x5 at f/11-22.

Thanks again for your thoughtful assistance.

[Doremus Scudder]

... Thanks again for your thoughtful assistance.

Philip,

I'm just having some fun kicking around ideas. Thank you for doing all the work!

It seems I didn't fully understand your previous post. Now that I do, your results seem logical. In any case, the SLIMT seems to make only a small difference in grain, if any. I'll keep an eye out for different renderings of delicate highlight values with and without SLIMT when I process now.

Best,

Doremus