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

Re: separations for gum printing

See the print made with RGB separations here:

See a 100% crop of the 400dpi scan here:

Print size is exactly 8x12".

As you can see I still have problems with smoothing the cyan layer. Will
try the foam roller solution later.

The actual print is a little bit less contrasty (enough for classifying it
as "unsuccessful" IMO), the slight contrast boost is a scanning artifact.


22 Kasım 2008, Cumartesi, 2:03 am tarihinde, Loris Medici yazmış:
> 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 yazmış:
>>> ...
>>> 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.