Re: solarized gums?
On Feb 15, 2007, at 1:10 AM, Loris Medici wrote:
http://www.pacifier.com/~kthayer/images/BU.jpg
Your step tablet print above (which looks slightly underexposed to
me -
will assume it was correctly exposed to make my point) shows paper
white
on steps 5 and 6, then stain in form of tonal inversion.
Loris, sorry, but I just noticed this last statement, which isn't
quite accurate. You may not be able to see the jpeg well enough to
discern this, but there is no paper white anywhere in that step
print; as I say in the accompanying text, but may not be evident
from looking at the jpeg of the print, those intermediate steps are
the lightest tones of the scale, or possibilty a combination of light
tone and stain; it's hard to tell, but at any rate, not paper white
at all. Step 5 has more tone than 6, but 6 isn't paper white
either. Both are either stained or toned enough to represent a
significant difference from paper white. In the examples of tonal
inversion I've seen personally, I haven't seen paper white on those
intermediate steps, but it looks like paper white on the one you
showed, and I think also on some that we saw in a similar discussion
some time back.
As to whether it's underexposed or not, I won't quibble, because I
don't remember which of the several similar-looking test strips I did
at various exposures was the one I grabbed to upload to represent
"tonal inversion;" the point of showing the strip wasn't to show a
perfectly exposed strip, but to show an example of "tonal
inversion." Whether it's underexposed or not seems to me
immaterial, since increasing the exposure didn't eliminate the
"inversion" whereas reducing the pigment in the mix did. But the
misunderstanding suggests that I should make that clearer either in
the text or by more careful or expanded choice of accompanying visuals.
Thanks for the discussion,
Katharine
What I
understand from this test is: I shouldn't use a negative density
above 5
x 0.15 = log 0.75 (or a density range above 0.75 - adjusting exposure
according to the b+f density difference between the Stouffer tablet
and
my actual substrate) for that particular coating mix. As someone
printing with digital negatives, why in earth should I change my
coating
mix - if I'm happy with its properties such as color, hue, density,
covering power... and whatnot - instead of making necessary
adjustments
in the negative? That is what I don't understand - since the step
tablet
test clearly shows me a way to protect / free myself from stain in
form
of tonal inversion = to adjust my digital negative's DR according
to the
properties of my coating mix.
Reducing the pigment/gum ratio may be a perfect solution in case of
using "in-camera negatives" (in other words; when dealing with
fixed DR
/ Dmax values) but it may not be the best remedy for someone using
"digital negatives" and determined to use that particular coating mix
(especially for making one-coat gums). That was my point/objection.
Regards,
Loris.
-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: Wednesday, February 14, 2007 8:02 PM
To: alt-photo-process-l@usask.ca
Subject: Re: solarized gums?
Hi Loris,
Well, this is the amazing and wonderful thing about gum, isn't it,
that no matter what someone says, other people will come back with
contrary observations or assertions. At the same time, I can only
speak to what I've observed myself, and that's what my web page
reflects, is my own observations.
Also, I think it would be useful for anyone following the link you
gave from the archives to read the entire thread, not just the post
that's linked. I would point to:
http://www.usask.ca/lists/alt-photo-process/2005/dec05/0479.htm
http://www.usask.ca/lists/alt-photo-process/2005/dec05/0507.htm
to give a more expanded perspective on those particular tests.
I guess we'll agree that the pigment concentration I used on that
print is not excessive since that is easily judged by the scan ->
this is Phtalo Blue; as we all know, this is a dark pigment with
immense covering power...
Unfortunately, your guess is wrong; I wouldn't agree to most of
those things. Sorry....
First, I'm not sure how one could tell just by looking at a scan
whether a particular pigment mix is overpigmented or not, since an
overpigmented mix doesn't look different from an optimally pigmented
(meaning pigmented to full color saturation for gum printing) mix.
Overpigmented, by my definition, simply means excess pigment added to
a mix after color saturation is already reached, so obviously more
pigment after that point isn't going to change the color saturation
or the value.
Second, I wouldn't say pthalo is a particularly dark pigment. It's a
medium blue, no darker in value than ultramarine and not as dark,
IME, as Prussian. I'm not sure it could be printed much, or maybe
any, darker than what you've got there, although I've been trying.
My stock mix (which I dilute considerably for tricolor work, since to
use it at full strength would make the tricolor much too dark) prints
at about the same value as your demonstration print, as far as I can
tell.
Also, I wouldn't use the phrase "immense covering power" for phtalo,
since my understanding of the term "covering power" is that it refers
to opacity of the paint layer. Pthalo is actually a very
transparent pigment; even at the heaviest concentration possible,
the layers underneath can easily be seen through the pthalo, which is
good because it allows the blending and mixing of colors from
multiple layers.
But while I wouldn't say pthalo has immense covering power, I would
say it has immense pigment strength, meaning that a little goes a
long way. Like lamp black, it takes considerably less pigment to
reach full color saturation than for most pigments, and by extension,
less pigment to reach an overpigmented state.
I'm printing a series of tests now, where twice and even three times
as much pthalo/gum as my stock mix don't print any darker than the
stock mix, and all three are about the same color saturation as your
example. (But not the same hue. I wonder if your pthalo is the red
shade; I use green shade pthalo --PB 15:3-- and mine seems a bit
greener than yours)
Here's a small page showing a test strip at 3x the pigment
concentration required for color saturation (in other words, 3x my
stock mix) which at least by eyeball looks similar in value to the
test strip you showed yesterday, and which is also essentially the
same value as a test strip using my stock mix, which is mixed to
color saturation. I also show on the same page what my usual mix for
tricolor looks like, which is something like 1/2 to 1/3 the
concentration of my stock mix (I can't give exact amount, because I
don't mix by weight or volume but by eye; I mix to match the color of
a paint swatch I keep handy for color matching for each pigment and
particular use) I didn't upload the entire series of test strips
because this doesn't seem a huge issue, and my available webspace is
limited and getting moreso all the time.
http://www.pacifier.com/~kthayer/html/Pthalostrength.htm
As to the immediate question, I haven't been able to produce either
stain or "tonal inversion" with any of the three pigment
concentrations (maximum color saturation, 2x maximum color
saturation, 3x maximum color saturation) using a number of different
exposures for each, so my tests with pthalo today don't support
either hypothesis (overpigmentation or underexposure) for "tonal
inversion." The 3x saturated mix is so pigmented that the hardened
dried gum layer looks scumbly,and dark deposits of pigment are left
at the ends of brush strokes, but I didn't get any flaking with it,
or any staining, as I said.
By the way, the term "tonal inversion" isn't mine, and I don't think
it's a very apt term, which is why I always put quotes around it.
But it's a term that's been used to describe this phenomenon, so I've
reluctantly used it to be consistent with others talking about the
same thing.
Katharine
On Feb 13, 2007, at 12:21 PM, Loris Medici wrote:
Hi Katharine,
This (as Ilana describes) is no doubt the phenomenon you name
"tonal inversion". I've read the page that you wrote about this
issue again and don't agree with you in:
"...The remedy, of course, the way to eliminate the tonal
inversion, is simply to reduce the pigment/gum ratio..."
Because I've experienced the same effect with a lightly pigmented
blue 31-step tablet print before. See:
http://www.loris.medici.name/Gum-Test-01.jpg
The scan doesn't show it well but, to my bare eyes there's
definitely paper white at steps 18, 19 (and maybe 20) + there's
definitely tone (where there shouldn't be) at steps 20+.
I guess we'll agree that the pigment concentration I used on that
print is not excessive since that is easily judged by the scan ->
this is Phtalo Blue; as we all know, this is a dark pigment with
immense covering power...
Regards,
Loris.
--------
Hi Ilana,
My own experience, observations and tests don't support the notion
that failure to clear (aka pigment stain) is a function of
underexposure, so I wouldn't agree with your tentative conclusion
that "parts that should clear are not, because they have not
received enough light." If you're interested, some test strips
showing the lack of relationship I found between stain and exposure
are here:
http://www.pacifier.com/~kthayer/html/stainexposure.html
It sounds like what is happening to your highlights, if I
understand the description accurately, is a phenomenon some people
call "tonal inversion." For my take on this phenom, see
http://www.pacifier.com/~kthayer/html/tonalinversion.html
Hope any of that is useful to you,
Katharine
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