RE: Back-exposing on plastic (was: Re: Gum transfer

Dave, can't wait to see your results. Just out of curiosity what is your UV
light source and what would be a printing time for say cyanotype ot
palladium in your setup? This should help me understand where this very long
exposure time is originating?
Marek, Houston

>From: Dave Soemarko <fotodave@dsoemarko.us>
>Reply-To: alt-photo-process-l@usask.ca
>To: alt-photo-process-l@usask.ca
>Subject: RE: Back-exposing on plastic (was: Re: Gum transfer
>Date: Thu, 04 May 2006 23:55:57 -0400
>
>Adjustment #2 is not that easy to do. I used to think that when I started
>with gum because I thought everything was linear simple math, but I soon
>found it wasn't.
>
>I started with a simple mix and got a nice gradation though the Dmax wasn't
>as black as I liked. It was like a dark gray. So I thought "that's simple,
>just add a little pigment." So I did and make another print, and the print
>turned out to be lighter! I thought it must be my inexperience in coating,
>so I tried a few more and found that they were also lighter. Then I
>realized
>that it was because with heavier pigment, there was a filtration effect, so
>the step tablet was underexposed.
>
>So I had to double my printing time. It was better, but I still couldn't
>get
>the maximum black. So I exposed more (3x), I still could not. That was
>because to achieve the darkest black the UV has to penetrate through the
>black pigment, and the deeper it has to go through, unfortunately the more
>pigment it has to cut through. The effect is that you have a long long
>shoulder on the shadow area.
>
>But that time, my exposure time is about 2 hours. I still hadn't got to
>maximum black with that coating, and I also hadn't got to maximum black
>that
>I desired by adding more pigment. By step tablets I could estimate that if
>I
>added more black pigment and wanted to achieve the max black, my exposure
>time is going to be at least EIGHT HOURS!
>
>I did expose one with 4 hours and got a beautiful gradation of about 10
>steps! but the gradation is not linear, so one must make a perfect negative
>that match the shadow, midtone, and highlight perfectly in order to use the
>system. I suppose with a perfect negative and exposure of 8 hours, one
>might
>be able to get a perfect single-coat gum print (perfect in a sense that
>every or most tones fall to or close to the desired density).
>
>That was when I decided that two coat gum is probably going to achieve the
>same thing easier and even faster. You can use a (or two) less-perfect
>negatives, but with flashing and different strengths of pigment for each
>coat, you can achieve what you want easier. The only thing is that you
>shift
>the problem from making perfect negative, perfect coating, and perfect
>exposure to the mechanical problem or registration with multiple coating.
>
>
>Dave S
>
> _____
>
>From: Ender100@aol.com [mailto:Ender100@aol.com]
>Sent: Thursday, May 04, 2006 12:48 PM
>To: alt-photo-process-l@usask.ca
>Subject: Re: Back-exposing on plastic (was: Re: Gum transfer
>
>
>Hi Katherine,
>
>Thanks for your response, I understand now what you were saying regarding
>the tonalities with gum-that's what I thought you meant originally, but my
>thick brain intervened.
>
>It would seem then that to get the "best" one print gum, then one would
>have
>to play with some variables, and you gummists have probably already done
>this.
>
>Starting with the best paper/sizing combination which prints smoothly with
>longest tonal scale, adjust the following variables until you get the
>longest scale on a stouffers, the highest Dmax, and smoothest tones.
>Obviously there would be tradeoffs.
>
>1. Adjust amount of dichromate higher for longer tonal scale until no gain
>is seen.
>2. adjust amount of pigment higher for greater dmax until tonal scale
>begins to fail.
>
>Other variables you could tweak?
>
>
>In a message dated 5/4/06 10:31:00 AM, kthayer@pacifier.com writes:
>
>
>
>
>Mark, I understand the theory here, but I also know gum, and I repeat
>that I have yet to see a one-coat gum that prints tones from dark to
>light, with all the tones in between. Maybe a better way of saying
>that is that given the kind of pigment load that you need to get the
>deepest DMax, the emulsion is going to be contrasty enough that there
>will be gaps between the tones rather than a smooth gradation.
>Surely you can see for yourself that Chris's gum print is jumpier in
>tone than the platinum print; throughout the portion of the scale
>that they both print, there are gradations of tone in the platinum
>print that just aren't there in the gum print. So while it seems
>theoretically to make sense to say that gum should print all the
>little tones between the DMax and the DMin, the fact is that it
>doesn't, not in one coat. Like I keep saying, I'm ready to be
>pleasantly surprised, and this is what I'm aiming for with the back-
>exposure experiments, but I have yet to see a one-coat gum that can
>print a delicate gradation of tones throughout a full tonal scale.
>Yes, of course, a one-coat gum can print a rather contrasty
>approximation of a fully tonal scale, I would have thought that went
>without saying, but like I say, there are "fully tonal" scales and
>then there are fully tonal scales.
>
>I do think Chris could get a better approximation to the smooth tonal
>gradation of the platinum by using less pigment, but then the
>question is whether you can get the DMax. Maybe, maybe not. And this
>is the struggle always with gum, as Sandy and Terry and many others
>have pointed out. More pigment means deeper DMax but more contrast,
>less pigment means more subtle tonal gradation but less DMax. This is
>the eternal equation of gum; it's got little to do with curves. Yes,
>if you've got a really bad curve to start with, as Chris has here,
>you can improve it, But you can't improve it beyond the limitations
>of the particular emulsion you're using, which I suspect Chris may
>have demonstrated in the prints she posted.
>Katharine=
>
>
>
>
>
>
>
>
>Best Wishes,
>Mark Nelson
>Precision Digital <http://www.precisiondigitalnegatives.com/>
>Negatives--The Book
>PDNPrint <http://groups.yahoo.com/group/PDNPrint/> Forum at Yahoo Groups
>www.MarkINelsonPhoto.com <http://www.markinelsonphoto.com/>
>
>
>
Received on 05/05/06-07:59:57 AM Z