Re: Gum Bichromate Printing Controls

TERRY KING (101522.2625@compuserve.com)
19 Mar 96 05:33:36 EST

Judy

You rightly asked that I should express the following sentence more clearly :

" Appreciable differences in behaviour of the colour usually result from th
amount of pigment that is needed for a given saturation. "
You can tell I have just read a book on colour theory.

If a colour reflects very little light, let us take the dark blue, indigo, very
little of it is needed to show up against a white background. This means that
there is little pigment to block the effect of the light on the dichromate and
thus the reaction between the dichromate and the gum. The reaction is faster.
With light colours,such as yellow, a lot of pigment is needed to show any level
of contrast against the white background; the increased amount of pigment blocks
the action of the light and slows down the reaction. Moral use strong colours
but dilute them more for lighter tones.

You say ;"

That's for starters. Each pigment has its own chemistry and each
manufacturer uses a different version of the "same" pigment. For
instance,I tried burnt sienna, by Rowney, Smith, Winsor Newton, Schmincke,
Holbein, & a few others I forget. All were different. And although I found
Rowney had "the best" burnt sienna, they had the worst ultramarine (never
would clear). Etc. Etc. Etc. "

That is why I stick with W & N. with very occasional use of pure pigment a la
Carole.

You say

"And don't dismiss gouache out of hand. It's excellent, superb, non-pareil
for one-coat gum. I also understand, BTW, that the legendary Steven
Livick uses gouache, among other colors. "

Fine, it's just that when I started it was multicolour gum that caught my
imagination. Here an opaque medium is inappropriate.

I have read, learned and inwardly digested your comment on humidity. But even in
Arizona and New Mexico and Alice Springs 10 ml is not going to evaporate from
the plate in the time it takes to mix it and transfer to the paper, sat twp
minutes.

And honestly Judy I am not that clever. I just try to follow the basic
principles of the process. I get my students to do the same and they produce
pretty good multicolour prints on my workshops. Some of these have gone straight
into portfolios for degree and masters submissions and onto gallery walls. Once
the results of a week at one university played a part in the department staying
in business.

Terry