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

Re: was Miracle size for gum now tonal range

Loris said:
I don't think I told "I get a longer tonal range". What I told was: "I
use / prefer negatives with longer DR", adding now: -to get the tonal
range possible with the particular coating solution is able to give.
Tonal range (as I understand it) is a function of the pigment and
pigment concentration to my knowing.
Ah, gotcha...

Maybe gum spectral sensitivity is way different than cyanotype,
therefore the same negative (color) that reads log 1.4 for cyanotype
translates to a lower figure for gum - I can't tell since I haven't
checked that with a real (silver) negative.
Ah. I agree that cyanotype and gum are both shorter scale processes, so it makes sense to me to be able to use similar curves/negs.

OTOH, I clearly remember posting
here a Stouffer 31-step tablet gum (thalo blue) test print showing 16
discernible steps (including dmax and paper white) a couple of years
OK then, you are getting 5 1/3 stops, which corroborates with my stop range for gum, too, and is way different than the supposed 2 stops the one author said. But what I was interested in was the difference between dichromate strength and tonal range...something I will have to do myself on sized paper (have it on unsized, not sized, when I was testing back before I bit the bullet and decided gum printing on sizing was much easier than not sizing).
BTW, I do get some color change in the darkest parts (blacks) of the
layer but not too much; it doesn't affect the midtones and highlights.
Does that counts as dichromate stain due overexposure?
Well, the way to find the answer to that question is to clear. You are right that the dichromate stain is not in the midtones and highlights, only in darkest darks, so it can give a false read. If you take dichromate alone and expose it (no gum) you can see how it just goes and goes, but essentially if you used that looong exposure for gum you'd bake a print.

FWIW I never clear, only step wedges when I am trying not to get a false exposure read. But it's funny because at one point in the late 1800's people were panicking because their gum prints faded over time and found out they were relying on the dichromate stain in the shadows to provide some print density when, in fact, over time in sunlight it does bleach to a pale sage green.