Gum calibration (was: Paper negatives- Ink Selection)
Hi Keith, What printer / ink and paper profile settings are you using? If you're using grayscale negatives (which in your case could be giving more than enough density range for gum), then you may switch to colorized ones which are calibrated to give just enough DR!? (If that's the actual reason of your relatively longer exposure times, of course...) If I remember correctly, you weren't using curves, right? You have someone very very competent in making digital negatives, who's living very close to you ;) Why not asking them? (If you haven't already + If the current exposure time is unbearable to you and/or you feel that you need to make some improvements... Not to my eyes though!) Maybe you can calibrate for a pre-determinated printing time (which you find is bearable) such as say... 7:30 (1 stop faster) for your case, which gives you a strong enough gum layer (has to be tested of course), then fiddle with your working parameters (coating solution, curve, development ect. ect.) to suit that printing time. It's right the opposite of the usual (which is to determine the standard printing time for "a particular coating solution + particular working parameters" with step tablet tests, then design the curve based on that). I find the usual approach equally awkward compared to what I just suggested -> with gum it's hard to be such consistent, to test every possible coating solution, and why in world would I want to leave aside all that flexibility provided by the process? Any thoughts? (Especially to Mark, Michael, Christina...) BTW, as a last note: if Keith's slow coating solution speed is due to low humidity in his working environment, can adding glycerin (or propylene glycol) to the coating solution (which are humectants) help to keep moisture? Are dichromates and glycerin (or propylene glycol) compatible? If not, then these additives could also help to thin the emulsion a little bit (for better spreading), not to the extent water does. Plus, as an added bonus, since they're part of personal lubricants (I imagine Mark making funny jokes here), I think they may also help in case of grabby paper like Masa? :)) Regards, Loris. 15 Ekim 2008, Çarşamba, 6:43 pm tarihinde, Keith Gerling yazmış: > Hi Loris, > > My gums require 15 minutes with oiled negatives. I would really like > to reduce this. Also, cyanotypes made with the same oiled negatives > require exposure times of 30-45 minutes. How does this compare with > others? It seems pretty long. > > Keith
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