Re: dark gums
Hi Ilana and Loris, This is interesting how you explain it all, Loris, to find out I do it pretty much as you--the film cannisters are only about 30ml if I am not mistaken and I mix my stock solution into a 60 ml container but use a bit more stock than you do in my final mix (and use colorized PDN negs, too) but I have found, too, that about 1/2 tsp/2.5ml coats an 8x10, and I mix my gum similarly. Here are some more notes that I didn't finish last night before I went to bed; it is always hard to determine causes of things, though, when not present while you are gum printing to see how you coat, brush, expose, size, etc.: Quickie guesses: 1. Flaking off of the image [too much gum, right?] Too thick layer. 2. Extremely long exposures that still provide little image, with pigment not coming out [too long of exposures? not enough contrast in negative? Too much pigment?] exposures shouldn't be that long--is your image not developing out or is it washing off? First, too long exposure, second, too little. 3. A bit of staining after the print has washed. Sizing not good? 4. uneven gelatin on one print--that showed up in the image. I think the gelatin was starting to cool. I had this happen once, the gelatin pooled as it cooled and was very thick in the center. Weirdly enough it didn't show up. But I had the funniest thing happen last week. I had sized a piece and apparently didn't overlap my brush strokes of sizing perfectly, and where there were gaps in the sizing I got lines of pigment stain. Of course in the sky. Magenta. Ilana, for monochrome work I can't see a reason to print out several negs.Christina, my negatives are digital inkjet. However, before reading your email my plan for tomorrow was to separate the image into 3 negs--RGB--but print them all black. But after reading your advice on controlling exposure and pigment I think I can print one negative with a full range and get what I want with multiple layers. In fact, I'm realizing that that is the only way to go, and that is a benefit of printing with gum. But heck, you never know, try it and see if it is different! Maybe you'll discover a new way of printing monochrome! Maybe the three negs will print in different places so that you will get a more even final layer, But if you are starting from a color image, then printing, let's say, R lighter, G medium, and B darker, then it will be similar to using a filter on a camera to change the tonal relationship of BW film, you know? For instance, if you print a light red layer, it may look more infrared? This sounds really fun, actually! Of course, theory here, not practice. But I could easily take one of my already separated gum negs and try it. I always mix up fresh each time but, I kid you not, one old gum printerOne question though, with the multiple printing/adding pigment, can I have my sensitize solution [gum, pigment and dichromate] mixed and then add pigment to it? [what length of time--if any--will the light sensitive mixture last?] Or do I need to add pigment to the gum each time, and then mix it with the dichromate? recommended mixing the stuff up, letting it sit 24 hours (!) before using it to coat with! So even though I have not tried it myself, it must be able to be done. One day in very humid Minnesota I let a cup of dichromated gum sit all day in the dark, although every hour I photographed the change so it did briefly see room light. I have that picture under CZAphotography.com, then click on Learning, then Gum Dichromate, and scroll down to the bunch of cups of dark orange. the next one is exposed with it. I know, it is not a user friendly page of my website but at least you can see what happens to dichromated gum arabic when it sits around for a while. You're also welcome to click on a pdf in that section that describes my gum printing process. YRMV as always. Also, I have a 30% saturated ammonium dichromate solution...would it be too much a variable to change this to compensate with/for exposure? Could I add more distilled water to this already mixed solution? Yup, up to a certain point adding water to the dichromate (using a lesser percentage of di) will slow down the speed and raise the contrast. The end, Chris Hi Ilana, What substrate you use for your digital negatives - is it plain paper or transparency film? And, what kind of lightsource do you have? Diluting your ammonium dichromate solution will increase the paper's contrast and decrease printing speed. FWIW, I print using "plain paper" digital negatives (black ink only) and 25% ammonium dichromate. My printing times are 4 to 6 minutes (cyan: 4 minutes, yellow: 6 minutes). My lightsource consists of 8x40W BL tubes at 3" from glass. I use pigment stock solutions; I pour all of the 15ml tube into film canisters, top it with gum solution. My gum solution is made by mixing 1 parts gum powder with 2 parts water (I use sodium benzoate to preserve it). I put very little pigment/gum stock solution in my coating solution (two thin - thinner than my little finger - spatulas per 5ml coating solution) and I coat very thin (haven't measured precisely but I use circa 2.5ml combined gum/pigment+dichromate solution per A4 / Letter size prints with at least 1" border - my coating tool is a foam brush). Regards, Loris. -----Original Message----- From: ilana [mailto:ilanamahala@adelphia.net] Sent: Wednesday, January 24, 2007 4:06 AM To: alt-photo-process-l@usask.ca Subject: RE: dark gums ... 2. Extremely long exposures that still provide little image, with pigment not coming out [too long of exposures? not enough contrast in negative? Too much pigment?] ... Also, I have a 30% saturated ammonium dichromate solution...would it be too much a variable to change this to compensate with/for exposure? Could I add more distilled water to this already mixed solution? ...
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