Re: gum "stain" with zero exposure... etc.
Two, three years ago, during a loooong thread on this inversion effect, I posted on the list that I observed this effect with gum on glass. I posted some pictures, even. So, the explanation by Mike Ware, with all respects due to him, is not enough for me. Also, the method of hardening is irrelevant in this case, since glass does not need any hardened gelatin coat. I used depolished glass.
On Wed, Oct 7, 2009 at 4:21 AM, Judy Seigel <email@example.com>
If you, we, or someone or other went back through the last 20 years (or so) of the list, reading every post with even a whiff of gum in it, I think some observations relative to the current observations would emerge. As is, certain points ring a bell...
For instance, the finding that an emulsion that had been exposed cleared better than one not exposed. Mike Ware saw that as a factor of viscosity... with a plausible explanation (below).
There have also been discussions of a kind of solarization in gum... of which I showed some examples in Post-Factory #3 (the whole reason for the P-F operation -- print on paper being better than human memory, at least this human memory). I only made it happen with certain colors, tho whether that was the pigment itself, or some additive the manufacturer put into that particular pigment, I don't know. (And in any event I didn't test it extensively as I had other issues in mind).
Thus on page 35 of P-F #3 we see a print by Sarah Van Keuren of a tree with very clear "mackie lines" in white, outlining the foliage.
Then on pages 37-38, titled "Funny Gum Trick: Direct Reversal, 'Solarized,'" I show some related effects I got.... AND give a plausible explanation, as follows:
"The baffling effect was that the less the exposure... the greater the stain. Mike Ware offered the only explanation to date: The less viscous the emulsion...the more it soaks into the paper, hence the more stain. The steps directly above the "legitimate" tones have had enough exposure to make them slightly viscous -- not enough to leave tone in the print, but enough to forestall stain..... My tests suggested it didn't happen on papers with gelatin size hardened in glyoxal, only in formaldehyde. Mike Ware thought that was because glyoxal hardens better...But it didn't happen on every paper."....
And a PS: When I run the world, I will forbid anyone to take up gum printing after they've done platinum (unless they have a brain purge inbetween), because it seems to me from descriptions on the list that folks attempt to print gum with the same kinds of precise/rigid controls and minute variations they learned in platinum. In this I believe they defeat the medium of gum, which begs to be handled freely... Yes, it will tolerate such handling, as it's very good natured, but my feeling to date is that the potential and scope of the medium is thereby muffled at best, lost at worst. (I mean if you want to make a C-print, call Kodak, or get an inkjet.)
On Tue, 6 Oct 2009, phritz phantom wrote:
those are the pigments i always use: dry pigments made by Guardi. and 16% gum, mixed from chunks.the paper is cheap paper from boesner with a very fine surface, sized with gelatin and chrome alum hardened. i have about 15 or so colours around, some of which i have used a lot, other not yet at all. i used the iron oxide black for the test strip, because the phenomenon first happened with a highly pigmented iron oxide/ phthalo blue mix, and i wanted to find out what's happening here. it later occurred again with the burnt siena. i don't normally use the iron oxide black, because i never got good results and it stains heavily.
i don't really think that the desk lamp is the source of error here, but i just wanted to check to be sure. also it's a somewhat strange spot light bulb- i don't trust it. but the working distance (when registering ) is about half the time (max.) at appr. 10 times the distance. this test strip just happens to be the only one, in which i left a part covered with cardboard, so that it won't get any exposure at all.
i mentioned the pigment-ratio-test, because this could maybe be another part in disproving the test. it is the part that got zero exposure which stains (if this is stain) the most. in the area that got some exposure the gum dissolves better than in the area which got zero light.
this is also my main source of confusion here.