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

This is amazing, Dave, and so opposite my own experience, I'm not
sure I can get there from here. With a heavy pigment load I get a
black as dark as the pigment (say lamp black that is concentrated
enough to be as black as black can be) with a very short exposure,
say one or two minutes), and more exposure doesn't increase the DMax
but simply extends the tonal range upward as far as it can go, which
in my experience isn't far with a heavy pigment load. It baffles me
that gum could work so differently in someone else's gum universe...
not to say I'm questioning your observations -- I'm not-- but how
could that be? Can the lights make that much difference? Anyway it
just shows how useless it would be for me or for anyone to assume
that how gum works in our universe must be how gum works for everyone.

The one thing you say that is corroborated by my experience is that
two gum coats will probably always give you a better tonal scale
(longer with smoother gradations) than one.
Katharine

On May 5, 2006, at 6:57 AM, Marek Matusz wrote:

> 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 05/05/06-10:57:25 AM Z