U of S | Mailing List Archive | alt-photo-process-l | Re: Gum tonal range (was Miracle size for gum)

Re: Gum tonal range (was Miracle size for gum)

Odd, I didn't get phritz's post, just etienne's response.

Yes, I'm talking about the tonal range of one printing. Understand, I'm not giving "the print tonal range of gum" as .75, it's just that those three pigment concentrations of iron oxide black printed an identical range of .75; the range just moved down the scale as the pigment concentration increased. But I'd have to do a whole lot more testing than I have any interest in doing, to make any general statement about the tonal range of gum. This pigment (PBk11) is a weak pigment and requires a lot of pigment to reach a particular color depth, so even the medium-dark concentrations have quite a lot of pigment in them., and the darkest one has a whole tube of paint dumped into about 15 ml gum, as I recall. It would probably be easier to get a longer scale with a carbon black that has a lot more pigment strength.

Marek's examples are the best tonal range I think I've seen in gum. I tried the bleach development and couldn't make it work for me; I've forgotten the details now, but he's definitely got it.

On reflection while cutting and hauling brush today, I'm not sure I'm entirely in agreement that the transfer function for gum is nonlinear, but I'm too tired to put my mind to it tonight. I do agree that it works better to work from a long-scale negative and print the various parts of the range separately, rather than to print with a shorter DR negative; this goes back to a discussion a few weeks ago. A light pigment load of almost any pigment will print heavenly subtle smooth gradations in highlights much like palladium, as long as the tones are there in the negative to print.


On Oct 12, 2009, at 4:51 PM, etienne garbaux wrote:

phritz wrote:

i've been wondering, is this discussion about exclusively about one-layer-gums? i think it is.
* * *
katharine, with your .75 density range, did you mean single layer or finished print?

I'll let Katharine speak for herself, but it seemed clear that she was referring to a single layer -- did you look at the link she provided? She clearly said in a previous post that to get smooth tones and wide DR, you need to make multi-layer prints.

the other thing is, that all tonal ranges are a continuum between black and white. there aren't any steps in reality. even in an extremely short tonal scale is every single shade of grey present in it. it's just a matter of a suitable negative to print them.

True, but.... It is all a matter of mapping. Mapping luminance values in the scene to density values in the negative that will enable you to further map them to the desired reflection densities in the print. This discussion has focused on the second half of that mapping, the transfer characteristic of the printing process -- how the various densities in the negative map to reflection densities in the final print.

If one is trying to get "every single shade of grey" in the final print, there are easier ways and harder ways. (As a side note, even printers who do not intend to use all the shades of grey in any of their images are probably well served by learning how to do so, just as singers who never intend to pop up and down an octave at a time in performance nevertheless are wise to do so when practicing.) Any high-contrast printing process makes getting smooth transitions and all shades of grey in the final print difficult. It's much easier to differentiate the tones in the scene clearly when you expose and develop the negative (i.e., make long-scale negatives -- as long as you don't run out of the film's capacity to render them), then use a low-contrast printing process to map the well-differentiated values in the negative to the final print values. (The same applies, mutatis mutandis, to digital imaging, as well.) Asking a printing process to amplify gradations -- to dig them out of a negative when they are barely there in the first place -- is rowing against the current.

Of course, gum printers come from this the other way round -- faced with a process that is inherently quite contrasty and nonlinear, how does one get the tonal range one desires? Multi-layer printing is one of the most powerful tools, as I understand it.

Best regards,