RE: solarized gums?
Hi Katharine, Apparently I had to use "tinting strength" instead of covering, thanks for pointing that out. BTW, the pigment I used for that particular test was same as yours, 15:3. I'm still insisting that it was a lightly pigmented emulsion though... Anyway, I want to return to the main/actual subject here: the remedy of "tonal inversion". You suggest to reduce pigment/gum ratio in the coating solution as the only remedy to the problem - that's what I'm objecting to. 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. 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 > >
|
