RE: Exposure times in tricolor gum off list
Currently not, but I did before (for multilayer gums, not tricolors) and in the end will probably revert to this strategy (for tricolors also) since I feel that I'm not completely satisfied with the results I get with all those painstaking / long calibration steps... Regards, Loris. P.S. I cc'ed this to the list... 18 Kasım 2008, Salı, 3:13 pm tarihinde, John Brewer yazmış: > Hi Loris > > So you are using a curve from another process that has a similar exposure > scale and adjusting the pigment/gum/dichromate ratio to fit it? > > Yes, sharing with the list would be a good idea. > > Best > > John. > > -----Original Message----- > From: Loris Medici [mailto:mail@loris.medici.name] > Sent: 18 November 2008 13:03 > To: John Brewer > Subject: RE: Exposure times in tricolor gum off list > > Hi John, > > I see that our patterns match, that's fine... > > About calibration, frankly I think gum is a PIA to calibrate with PDN > and/or ChartThrob. It's just too hard to be as consistent as these > workflows require. I currently use a single curve devised from M tests > (which is not a perfect solution) and may opt to design color-specific > curves later depending on the results. I'm not after a super-balanced > perfect color representation, just an approximation... > > My recommendation would be to use a predictable / repeatable process which > is close to gum in terms of exposure scale (such as 2A + 1B cyanotype), > and use the curve devised from these tests for printing gum. Of course, > you'll have to adjust your coating solution to offset the longer exposure > scale of cyanotype (= stronger dichromate, maybe 1 + 1 + 2 sat. PD or 1 + > 1 + 1 15-20% AD...) IME, the best results comes from negatives optimized > for Cyanotype (much better shadows separation / detail). > > My reasoning is = if it's OK to use the same in-camera negative (or > similarly exposed / developed in-camera color separations negatives), and > still get good results (as shown by previous practitioners), perhaps we > shouldn't struggle much with color-specific calibrations... > > Maybe we should share this with the list? > > Regards, > Loris. > > > 18 Kasım 2008, Salı, 2:49 pm tarihinde, John Brewer yazmış: >> Hi Loris >> >> I'm replying off list as although I'm a competent gum printer with film >> negs >> I'm trying to do tri-colour with digi negs and am struggling a little. >> In >> the last couple of days I've made a couple of prints and my exposures >> are >> 4 >> mins C, 5.5 mins Y and 4.5 mins M. I use 2Y + 1M + 1C too. However my >> paint/gum/dichromate mix is 1 part paint gum solution + 1 part gum >> solution >> + 1 parts saturated potassium dichromate solution. >> >> There is still some tweaking to be done and I think this is a curve >> problem. >> How do you arrive at getting curves? I'm using Chartthrob. I can't use >> PDN, >> (because of the cost/licence restriction), as I'm hoping to teach >> tri-colour >> in the summer to students who have financial difficulties - I work for a >> mental health charity who use art as therapy. >> >> Best wishes >> >> John. >> >> -----Original Message----- >> From: Loris Medici [mailto:mail@loris.medici.name] >> Sent: 18 November 2008 12:21 >> To: alt-photo-process-l@usask.ca >> Subject: Exposure times in tricolor gum >> >> This goes mainly to tricolor gum printers printing from digital >> negatives >> separately calibrated for each color layer: do you experience any >> exposure >> time variation? If yes, can you please tell me your exposure times (and >> dichromate strenght, only if it isn't kept constant) for each layer? I >> just want to see if there's a correlation / connection... >> >> I balanced the pigments according to 2Y + 1M + 1C. In other words, my Y >> stock paint:gum solution contains 2x paint compared to both M and C >> solutions. Using the same coating solution formulation (which is 1 part >> paint:gum solution + 1 part gum solution + 2 parts 10% ammonium >> dichromate >> solution), I find that yellow requires the most exposure whereas C >> requires the less (M in between). Is this similar in your case? >> >> Thanks in advance, >> Loris.
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