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

Re: Gum Separations Using Indexed Color

Michael Koch-Schulte wrote:
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.
Some years ago I made some gums selecting colors with photoshop and then printing those negatives with opaque or semi-opaque colors. Like you, my process was to study first the main colors in the original picture and then selecting the most appropriate ones. When printing, the reconstruction becomes a very pleasing mental exercise because you can use colours which are different from the original though the look of the final print is what I would define "likely".
My prints are posted in www.grupponamias.com, going through authors>Alberto Novo>Venetian gums
There is also a brief description of this process under "articles"