U of S | Mailing List Archive | alt-photo-process-l | Re: Gum Separations Using Indexed Color

Re: Gum Separations Using Indexed Color

Thanks Keith,
I'm in the middle of this project at the moment (Xmas is taking up a lot more time with the kids out of school). I'm currently trying to output the negatives for the various colours I want to use. These ideas formed over the last few months. I've been doing a lot of painting lately, something new for me. I've been studying a lot of "colour theory", colour mixing and paint palette layout, etc., noting the differences between translucent, semi-translucent and opaque pigments. I quickly realised how this could be useful to expand the colour range in gum. [I recommend that anyone contemplating gum printing take at least an introductory course in painting and with a focus on colour selection or if you have to do self-study like me. This will give you a certain amount of knowledge in pigment use, you will learn "colour index names" and the properties of various pigments, hopefully.]
The idea of using a limit colour palette in a painting is what first trigger the notion of using six to ten colours rather than three or four as is common in gum printing. What is known as a "split primary" palette has a painter set up two yellows (one warm and one cool), two blues (one warm and one cool) and two reds (one warm and one cool). What I mean by "warm" and "cool" is that the colour are biased slightly toward their adjacent colours, therefore the first yellow is bias toward orange, the second yellow is biased toward green, the same goes for the red and blue. One red bias toward violet the other toward orange, one blue bias toward violet the other toward green. It's somewhat similar in concept to what an Epson printer does with it's inks -- but not exactly.
My other area of study has been concerning what silk screen shops and high end print shops print multi-coloured material by using "index" color. This is a somewhat subjective process which involves selecting dominant colours in the original work and creating dithered plates or negatives which blend solid opaque colours to recreate the original work.
I'm also thinking there is a middle ground with lots of room for my own subjective use of one method or the other, transparent or opaque pigments for filling in areas similar to how a painter "blocks in" shapes and colours early and then refines the look of the work with lighter transparent layers and "washes" later. I'm curious to hear for people on the list who are also painters. I'll post some results in the New Year. BTW, cheers and Happy New Year.!

Keith Gerling wrote:
I had discussed using spot color channels in order to add vivid and
bright additions of color in cases where my three-color gums were
using a muted pallete. It works, but couldn't help but think that it
would be easier to just hand-color the images.

I'm not sure why indexed-color would give you an advantage with opaque
colors. Did you try it?


On Wed, Dec 24, 2008 at 9:11 AM, Michael Koch-Schulte <mkochsch@shaw.ca> wrote:

Has anyone experimented with using Photoshop's "Indexed Color" function to
produce colour separations for Gum Bichromate? Or, mixed Indexed Color with
CMY(K) separations? Seems someone (Keith Gerling maybe?) was doing something
similar with adding extra channels to print pure colours. Indexed Color
would allow one to use opaque inks. I'm going to give this a try over the
holidays but would like to hear experiences from anyone who has done
advanced colour separation techniques. Thx. Merry Christmas.