Re: Gum dichromate issue

From: Etienne Garbaux ^lt;>
Date: 08/10/04-02:47:35 AM Z
Message-id: <p05210603bd3e3bfe595e@[]>

Giovanni wrote:

> I do my threee negatives with Photoshop and I print full color
> confortably, I am trying to learn and read more to avoid possible
> mistakes. Most of my errors come from specific pictures so the proper
> negative is an issue, sometimes I change the curve factor (on
> photoshop which is the contrast in a conventional film) on the Red
> negative but again I am guessing. Why? I read somewhere that it was
> the most important of the three negatives. Why? Is the first I use to
> print, then I go with the Blue (Yellow pigment) and I start guessing
> the solar exposure time and finally I do a third guess with the
> magenta pigment to "see" the picture. The other issue is the pigment,
> remember "pure colors" do not exist, how should this be dealt or
> handle in reality?

Well, if what you want is the most accurate color possible, I suppose
you would start with color densitometry. You would shoot a grey scale
card, then tinker all the variables (and there are ever so many of them
in three-color gum!) so that the print had no color cast in any of the
steps. That is why you would change the curves of the individual
separations -- to remove skew (the change in color balance with tonal
value). DT was a well-characterized process, so there were useful
generalizations. No such luck with three-color gum ("TCG"). You are on
your own.

There have been a number of useful discussions on the list of the best
pigments for TCG and three-color carbon/carbro. If you search the
archive, I'm sure you will find them.

In another message, you asked about Hubl's Three Color Photography. I
searched AbeBooks ( and found four copies,
from $100 to $200. If you can read German, there is another, less
expensive Hubl book called Dreifarbenphotographie that you might

Best regards,

Received on Tue Aug 10 02:48:06 2004

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