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

Re: separations for gum printing

Thanks for concern, but no, it's like it's been with me and your site
for the last few months: clicking the link brings up your page, but
with no image on it, and if I click on the "Marek's Gallery" tab at
the top I can get the gallery thumbnails, so I can see the one
thumbnail for each series, but if I click on a thumbnail, nothing
happens, I just get the same kind of blank page with the menu bar
across the top as I did in the first page. Someone suggested that I
could see the pictures if I clicked on "slide show" but for some
reason that option isn't available to me. But I guess I can sort of
get an idea

Umm, the purpose of printing a grey patch in gum with the different
separations wasn't to show what would happen if you ever wanted to
print grey patches in your tricolor prints, but to show the color
bias that the default Photoshop settings introduce into a file.
Printing a grey patch, for demonstration purposes, simply makes it
easier to see the bias, but the point is that it does that with ALL
the colors, not just with grey. But if you're adjusting for that in
other ways, I'll bug out; just wanted to be sure you were aware of
that bias.

On Nov 22, 2008, at 9:06 AM, Marek Matusz wrote:

I guess I need to read some more on the subject. The CMYK options
is very confusing and I remember a discussion on the list a while
back that pointed me to do some experimentation. I kind of
rebalance the negatives by adjusting the curve up or down, rather
then full with pigment concentration for my first pass.
ANd I never intend to print perfectly gray light, dark and middle
pathches on my tricolor gums.

Here are some examples of the last few prints. Thye are kind of
dull on the screen, I should have adjusted them a bit. On top of
CMY separations I have been experimenting with sawdust development
for a Fresson look.
(Katharine, I hope you are able to see them)

> Date: Sat, 22 Nov 2008 08:07:49 -0800
> From: kthayer@pacifier.com
> Subject: Re: separations for gum printing
> To: alt-photo-process-l@usask.ca
> Maris, the thing about default CMYK, even with K set to zero, is
> that it alters the color values to fit the requirements and
> limitations of commercial printing processes with high speed presses
> on slick coated paper, with inks especially formulated for those
> papers. How the separations deal with these requirements and
> limitations, in general, is to cut back on magenta and yellow in the
> separations while leaving the cyan at about the same value. This is
> how the separations have to be tailored to make the commercial SWOP
> process inks print "right," but it doesn't work for gum very well at
> all.
> If you go to this page
> http://www.pacifier.com/~kthayer/html/C MYK.html
> and scroll down past all the text-heavy explanations of the default
> Photoshop CMYK settings, down to the last visual on the page,
> there's a demonstration visual I made by printing a neutral grey
> patch on gum from (a) RGB-CMY separations (separations made by
> inverting RGB directly to CMY -- if anyone is unclear on how that
> works I have another page on that here
> http://www.pacifier.com/~kthayer/html/RGBseps.html)
> and (b) CMY(no K) separations. You can see, both from the color
> values in the file and from the printed gum patches themselves, that
> while the RGB separations print a reasonably neutral grey patch, the
> CMY separations with k set to zero print a heavily cyan biased
> By the way, I find it curious that people say they can't make heads
> or tails of RGB separations, they all look the same, but CMY(K)
> sep arations seem more intuitive. I'd say exactly the opposite,
and I
> think it's probably more what you're used to. To me, RGB separations
> are straightforward but CMYK separations don't make sense. :--)
> I enjoy seeing how people tailor separations to their own needs and
> desires; I'm not arguing that you shouldn't print CMY(no k)
> separations, but just pointing out how they are calibrated in such a
> way that they don't produce a neutral color balance when printing in
> gum with balanced pigments. So if you're going to use them, you
> might want to cut back on the concentration of your cyan pigment to
> match. To me, it just makes more sense to print with the straight
> CMY separations you get from inverting RGB, that way I know that I'm
> working with the color values straight from the original file, not
> distorted to meet the needs of some printing process that has
> to do with gum printing, but if you like the CMY(K) separations
> better, you may want to read through my discussion of the default
> settings and see where you could change the settings. It's been
> years since I've spent a lot of time with that, and I might not be
> remembering this right, but to the best of my recall, I couldn't
> a way to change the settings enough to get the values back to
> straight CMY. (And if you could, of course, then they would be
> identical to the RGB-CMY separations that you don't like).
> Katharine
> On Nov 22, 2008, at 6:32 AM, sam wang wrote:
> > Hi Loris,
> >
> > In CMYK, the black (K) is doing a lot of definition in the mid to
> > lower tone areas. Part of the reasons for using CMYK is to avoid
> > too much ink pileup in very rapid press runs. That's why in order
> > to use it, it is imp ortant to specify exact requirement for your
> > particular needs, otherwise leaving it at default may be fine for
> > the run-of-the-mill offset, but way off for your alt.
> >
> > To see the differences, you might duplicate an RGB file and
> > the dupe to CMYK. Then duplicate both of these and invert them to
> > negative. Then compare the channels of each file and the
> > differences would be very evident. (By the way, your example looks
> > like you inverted it to negative BEFORE converting to CMYK.
> >
> > Back to Marek's original question - RGB is the "quick and dirty"
> > way to separate colors. CMYK with K set to 0 may be better for
> > but likely it would require some tweaking - it's another case that
> > there's no sure way for everyone or every situation. (Would
love to
> > see some resulting gums when you hav e them, Marek.)
> >
> > Sam
> >
> >
> > On Nov 21, 2008, at 7:03 PM, Loris Medici wrote:
> >
> >
> >> See the comparison here:
> >>
> >> http://www.loris.medici.name/gum/RGB_vs_CMY/
> >> (Curved negatives from RGB and CMY K=0 separations.)
> >>
> >> Regards,
> >> Loris.
> >>
> >>
> >> 21 Kasım 2008, Cuma, 11:09 pm tarihinde, Loris Medici yazmış:
> >>
> >>> Hi Marek,
> >>>
> >>> I first planned to start to make color gums by CMYK
separations -
> >>> > because
> >>> it seemed natural in context of "printing" + because it was the
> >>> method
> >>> used by Keith. (I had not done anything serious with gum other
> >>> than few
> >>> step tablet tests before participating his workshop...)
Anyway, I
> >>> dropped
> >>> the idea and started with RGB separations because it required
> >>> only three
> >>> negatives, in other words less costly (1. both negative cost
+ less
> >>> layers) (2. yes K=0 also requires three negatives, but I wasn't
> >>> considering this at that time, and probably would not in the
> >>> future, if I
> >>> wasn't reading your message).
> >>>
> >>> I have an image which is currently giving me a hard time; I get
> >>> perfect
> >>> highlights and midtones but muddy / lifeless / flat shadows. I
> >>> tried to do
> >>> CMY K=0 separations and when I inspect the negatives on screen I
> >>> see that
> >>> it would print even worse, because there's no useful detail
in the
> >>> shadows. The RGB separations show good texture in the shadows,
> >>> compared to
> >>> the CMY separations. How come?
> >>>
> >>> Regards,
> >>> Loris.
> >>>
> >>> P.S. I'm at my mother's house now, will post the comparison
> >>> images later
> >>> and ask for your comments.
> >>>
> >>>
> >>> 20 Kasım 2008, Perşembe, 8:52 pm tarihinde, Marek Matusz
> >>>
> >>>> ...
> >>>> 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
> >>>> different methods of generating separations for tricolor gums.
> >>>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >>
> >
> >

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