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,
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