Re: tonal inversion and pigment loads

From: Yves Gauvreau ^lt;gauvreau-yves@sympatico.ca>
Date: 01/27/06-12:43:58 AM Z
Message-id: <00f601c6230d$b63bd7c0$0100a8c0@BERTHA>

Tom et all,

your image definitly trows a hole in my theory. I tried the experiment as I
said I was going to do but I can't say much about it, lets just say I should
have changed only one variable at a time and I didn't.

The shortest exposure sample seems to have produce the worst effect. On each
sample, after the "paper white" I presume (possibly staining also), the tone
seems to reverses and peak at a rather uniform value even across the
different samples (if we exclude the numbers of course). To me this suggest
something very similar happens to each sample and it seems as it is not
(directly) related with exposure and not (directly) to heat either. In other
words what doesn't add up is this uniform tone he gets above paper white
(gray). As for the numbers, well I have no idea, simple as that. On my step
tablet, which is not the same as the one Tom used, my number are a light
pale gray in a black circle but still I'm sure his numbers have the same
density and it should mean each number should print to exactly the same
value and all I can say is it doesn't happen that way.

The suggestion of printing a coat light on pigments and long on exposure,
another medium on pigment and medium on exposure and a last coat heavy on
pigment and short on exposure would seems at first, more and more
"illogical" as Spok would say. I already ear your complaints but keek
looking at the image below and you'll see in the 1m exposure that the tone
present from about step #8 would cover-up step #8 and above on top of what
is already there in the 2m sample and render practically useless the 4m
sample because anything above step #8 wouldn't be white any more. But I'll
give you this, the test Tom made is not exactly what is usaully done, first
coat low pigment, long exposure, etc. and this is a STEP-TABLET don't
forget. Even so the high pigment short exposure would still invert and cover
up most of the first two coat anyway, UNLESS... So probably your cheating
and you must fight to keep your highlights at the value you want all the
time. I suspect after ten years or more, one doesn't even think about this
any more, it as become a second nature. OR, OR, the big OR you use negatives
with a relatively low density range, 1.0 and probably better if less, most
probably no cheating required also. In other words, the perfect scheme...

Another way around this, is to have 3 negatives having no density higher
then the one corresponding to the "paper white" for the given exposure.
Should save some work to. For the longest exposure and a REAL negative I
suspect you wont have a reversal or whatever it is called. But I'm affraid
if you have a negative with a DR much above 1.0 (3 - 3 1/2 stops) possibly
better below 1.0, you will always have what is called inversion here and
you'll have to work to get it out if it can get out and that remains to be
seen.

Regards
Yves

----- Original Message -----
From: "Tom Sobota" <tsobota@teleline.es>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, January 26, 2006 7:08 PM
Subject: Re: tonal inversion and pigment loads

> Probably the reasons for tonal inversion are simple and straightforward,
> once we understand them, but for now the situation looks pretty complex
> and not easily interpretable.
> Please look at this test image:
> http://usuarios.arsystel.com/tksobota/Inversion-1.jpg where in the
> leftmost strip we see not one but two separate inversions:
>
> 1. From step 1 to step four we see the expected gum response to
> increasing negative density.
> 2. From step 8 to step 16 we see an inversion with several well marked
> inverted steps. The letters are black.
> 3. From step 17 to 21 the black letters turn to white, but the inverted
> background does not change.
>
> In the middle strip this 'secondary' inversion of the letters has
> disappeared, except possibly in step 21. In the leftmost strip no trace
> remains. The only difference between the three strips being exposure I
> can say positively that yes, at least _some_ inversion is affected by
> exposure.
>
> However, before someone feels the urge to eat her words, I must add that
> in other tests, with different sizing and/or different paper (but
> identical gum/pigment mix and exposure) the inversion does not happen at
> all. I think that the substrate is far more determinative of inversion
> that pigment concentration or exposure. But this is a tentative opinion,
> for now.
>
> To give an example: I prepared some sheets of Fabriano 5 for the oil
> process. I took one of the heavily gelatined papers, fixed in formalin,
> and applied to it the same mixture as previously. I found no trace of
> inversion nor of stain.
>
> The pigment used is Ivory Black from Maimeri in a rather low
> concentration. This pigment has low covering power, perhaps because the
> grains are relatively big. They are so big that some percentage of them
> can be seen and manipulated under a not-too-large magnification.
>
> Looking at the 'inverted' areas through a binocular loupe, what is
> inmediately striking is that the dark areas consist of mostly loose
> pigment grains. These grains, far from being imbedded in the paper
> fibres, just lie on the top of it. They are too large to get between the
> fibres anyway. When the gum is still wet, the grains can be seen movin
> in the small water 'puddles'. They should just wash away ... but they
don't.
>
> Fascinating, but far from having been explained, in my opinion. Some
> more experimentation is necessary. And even so, it is very difficult to
> abstract one's working methods and materials so that results can be
> extrapolated to other workers. But we already know that...
>
> By the way, I am not of the opinion that gum has a limit in the quantity
> of pigment that it can hold, and that staining is the result of the
> pigment 'having to go somewhere'. Solutions have a saturation point but
> gels do not. Any tube of watercolour is the proof that gum can hold more
> pigment than we ever use in gum dichromate.
>
> Tom Sobota
> Madrid, Spain
>
> Katharine Thayer wrote:
> >
> > I haven't yet seen any credible evidence that one can eliminate
> > either pigment stain or inversion by increasing exposure, but I have
> > eliminated both of them simply by changing the gum/pigment ratio. I
> > have seen some evidence, in Tom's (I think it was Tom) posted test
> > strips, that one can move the inversion up or down the step tablet by
> > changing the exposure, but again that seems rather obvious and trivial
> > to me; of course changing the exposure alters where the tones appear
> > on the step tablet; more exposure blocks the shadows and sends the
> > meaningful tones farther up the tablet, but so what? The meaningful
> > tones are still the same tones, and the pigment stain is still there;
> > the only difference is your shadows are all blocked. The crucial
> > variable in the inversion, as far as I have seen, is overpigmentation,
> > and if the gum is overpigmented, you'll either get stain or inversion
> > or flaking or something, because the extra pigment has to go
> > somewhere, and the way to fix it is not to expose more, but to reduce
> > the pigment, in my experience. (It should be clear from the test
> > prints that I posted that reducing the pigment enough to eliminate the
> > stain does not mean giving up printing with a fully saturated pigment).
> >
> > One caveat: I did see an oddball thing where someone sent me an
> > inversion he got with a very small amount of pigment; he then got a
> > positive image with the same pigment mix by exposing more, but at the
> > same time he increased the exposure, he changed other variables as
> > well, so it's impossible to say what caused the improvement. Which is
> > why you should never change more than one thing at a time.... at any
> > rate, he was using blue photofloods for the exposure and my experience
> > with them suggests they don't behave like normal lights do. So that
> > one seems like an anomaly to me, unexplained and unexplainable without
> > further investigation, one variable at a time. When someone can show
> > me an inversion with a light pigment load that goes away with
> > increased exposure, all other variables held constant, indicating that
> > inversion is a function of exposure rather than pigment load, then
> > I'll eat my words, or a few thousand of them anyway, but I can't eat
> > my pictures. If anyone's interested in a full treatment of my
> > position on pigment stain, I just uploaded that revised page last
> > night. There isn't anything particularly new there; I've said and
> > showed all this here before, I think. One of my goals on revising the
> > site was to cut down on the text, as no one seems to read it anyway,
> > but I don't seem to have accomplished that.
> >
> > http://www.pacifier.com/~kthayer/html/stain.html
> > Katharine
> >
> >
> >
> >
Received on Fri Jan 27 00:46:59 2006

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