U of S | Mailing List Archive | alt-photo-process-l | Re: again on color absorption

Re: again on color absorption

On May 12, 2009, at 7:34 AM, Katharine Thayer wrote:

Ah, that makes more sense than the explanation for a one-time only appearance of this phenomenom in gum (on an HSL array) which was advanced on the hybridphoto site, and which has been advanced on this list from time to time, that the tonal inversion is a function of underexposure, or because the "negative" had too long a density range for the process. Both those explanations were easily refuted; this one has some merit in your case, especially if it happens every time. Mine, as I said, happened only once in many printings of the same HSL array with the same light source and correct exposure time, so this explanation wouldn't work for what happened in my case any better than the other ones did.


Loris wrote:

Katharine, the only case I can remember that you have brought this issue
(gum tonal reversal, that is) into consideration was your 21-step tablet
test prints on glass - not HSL array... So nothing is refuted (as well as
nothing is proven) in my view -> since these two are completely irrelevant

Loris, apparently your memory is faulty, since I've brought a number of examples into the discussion here, many of which are included in my web page on tonal reversal in gum. But the example I referred to specifically was one of an HSL array I printed in gum that showed this reversal, that came up in the midst of a discussion on hybridpthoto about choosing a good blocking color. I didn't bring it up here to revisit that discussion ( discussions about tonal reversal in gum are more aversive to me than I can say), and in my brief mention of it I wasn't claiming to have refuted anything in general about gum tonal reversal, only to have refuted explanations for that particular example of it. If you're interested in the discussion, it's in a long thread on hybridphoto; the relevant portion starts on page 7 of the thread:


I only brought it up here as an illustration of the wide variety of opinions about the cause of tonal reversal in gum. When noticing the reversal on Alberto's HSB print, I was just curious if the causes of this are more straightforward for metal processes than for gum.
Katharine Thayer

On May 12, 2009, at 2:09 AM, Alberto Novo wrote:

Katharine, IIRC, the portion below the dashed line (pure color) would be
less colored ink(s) + more black ink (due to less lightness/ brightness -
depending which test pattern is used) as you progress more to bottom.

Now I am undestanding...

my understanding of Alberto's test would be that black ink isn't as opaque
to the specific light which that specific process requires as some other
colored inks, that's why there's reintroduction of tone. This is something
I experienced with Epson 890/1290 OEM dye-based inks and HP9180
pigment-based inks.

You are right, the mixing of colour with black decreases the amount of both. The absorption of pure black is in the last row, which is a little denser (absorbing less) than pure green.