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

Marek,

It was a bank of 8 BL tubes, 24" each. I don't print cyanotype or palladium,
so I have never tried it that way. The long exposure and concentrated
pigment and thick emulsion give me a very long scale in gum though (10 or
more *clearly distinctive* steps).

But this was not a new test. It was done about 7 or 8 years ago.

Dave S

-----Original Message-----
From: Marek Matusz [mailto:marekmatusz@hotmail.com]
Sent: Friday, May 05, 2006 9:57 AM
To: alt-photo-process-l@usask.ca
Subject: 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 05/05/06-03:50:25 PM Z