U of S | Mailing List Archive | alt-photo-process-l | Re: separations for gum printing

Re: separations for gum printing



Hi Marek,

With my admittedly limited experience with tri-color gums, my times are also fairly similar-- but I do think I also compensate with development time.  I did make a few CMYK prints, though (with the K printed as pt/pd), but those digital transparencies generated from CMYK (as opposed to CMY) are vastly different.  No need to even mark which is which, and --yes-- the differences are also easily seen onscreen.  Since I didn't print the black as gum, only as platinum, I didn't really get to appreciate what a CMYK would be like-- all gum-printed.  Never used RGB, though.

Diana


On Nov 20, 2008, at 1:52 PM, Marek Matusz wrote:



All,
This recent discussion on tricolor gum printing sparked my interest. My printing times are about the same with all colors, but perhaps I compensate with development time, these two variables are related. But that is not what I wanted to discuss. Mostly everybody agrees that B channel (in the RGB color space) intended for yellow printing always requires a different curve then RG channels. This is also my observation and practice. The B channel is almost always much 'flatter" then oher channels and requires a more pronounced curvature. Quite frequently I do not have enough definition in the B channel to get enough contrast resulting in prints with overall yellow cast.
Since CMYK space and separations are intended for printmaking, which is what we do in gum I started making CMY separations with K set to zero. There is a visual difference on how the pictures look on screen in these two color spaces (anyone interested should try to toggle between spaces in Photosop) and also how the Y separation looks compared to B channnel in RGB color space. It also seems like the colors are less muddy. I have only done a few pictures so far, but I want to see if anybody is doing different methods of generating separations for tricolor gums.
Marek 


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