Re: Paper negatives- Ink Selection
15 Ekim 2008, Çarşamba, 7:07 pm tarihinde, Christina Z. Anderson yazmış: > > ... > > Loris, > Not to butt in on this dialogue you all are having, but I thought I'd > re-remind you that a 10% am di is not equivalent to a 10% pot di--it is > faster. 10% AD is about equivalent to saturated PD, which is something like 13% at room temperature. PD solubility in 20C / 68F is 12% (according to MSDS), at 22C / 72F (room temperature) should be slightly more (about 13%, empirical). AD molar mass = 252.07g, 100 (10% in a liter) / 252.07 = 0.39M PD molar mass = 294.19g, 130 (13% in a liter @ 22C) / 294.19 = 0.44M and 120g PD (12% in a liter @ 20C) / 294.19 = 0.40M Accepting there isn't any factor affecting speed (chemically) other than molarity of dichromate ion in solution(!?), then in theory, due to slightly stronger concentration (0.44M > 0.39M), 13% PD should be slightly faster than (or about equivalent to) 10% AD. I assumed Keith's workspace / chemistry storage isn't colder than 20C / 68F... Thanks for reminding though! :) BTW, I think it's better to use solutions slightly below saturation levels (for instance I never mix more than 10% PD and 25% AD) because I think it aids in consistency. > ... but it was posted to the list a while back by Sandy King, > and then I think even by you and Alberto haggling out the > percentage. That can account for some of the difference. There can be a slight difference, but 1.3 stop seems way too much for attributing it solely to minute difference in dichromate concentration. > Also, is it more humid in Turkey? Not necessarily, Chicago's humidity (and temperature levels) should be close to Istanbul's in this season. Core winter or summer time can be more different I presume... > Also, thick vs. thin layers, etc. etc. I find that the > way > one brushes on a gum coat is probably the biggest reason for success and > failure. The thinner the better. Very true, that's what I'm getting through -> the more proficient(!) I become in coating, the better gets my results. I think, along with choosing paints/colors (which is also very important), coating is the part which you need the most finesse in gum printing. > But all of that is determined with > overlapping the step wedge with the substrate of choice so it might be > helpful to send a small strip of your substrate of choice to each other or > I > probably forgot it was the same stuff didn't I.... Yes you did ;) > ... > I have 1 1/2 days next week to teach a class in Missoula MT how to do > perfect gums so we'll see if it is possible :) But how the heck I am going > to do that when I am in a full leg brace is a totally other story. What a pity! For how long it will stay? Good luck in rehabilitation... Regards, Loris.
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