RE: Gum dichromate issue

Hi Giovanni, the inherent nature of gum means that it is imprecise -
often you DO have to print a layer again...anyway, as far as I know this
could be improved if you do the following - always stick to the same
pigments and test them thoroughly for strength. Some pigments are
stronger in colour for their volume than others. For instance, yellow
can often print at much greater apparent density than other colours.
This will upset the colour balance. Cyan is somewhat self-masking, and I
don't know if this is true for other colours. I assume the more opaque
the pigment, the more it will self-mask.(any comments???) I have a
problem with the magenta pigment I use - it's very hard to measure
accurately (tube paint) and just a little too much throws the balance
way out. It's hard also to distribute the pigment evenly throughout the
emulsion - often it will fall to the bottom of the vessel and you will
get stronger pigment in the last prints. This can be helped of course by
stirring frequently (remembering to is my problem).

As for reprinting the cyanotype layer - do you double coat? I find I get
better density that way. Reprinting in cyan might not be a good idea, I
don't know...someone else will have to answer that. I usually reprint in
gum if I need to add cyan.

There are so many variables in gum that it's hard to know what went
wrong - or right. Two identical prints made at the same time can vary
significantly from one another - it's one of the noted features of gum.

If you have problems with a layer of a specific print, I would try
reprinting the negative for that layer with greater or lesser density
depending on the problem. Do you use CMYK or RGB?? I can't remember. OR
add a little more or less pigment to the emulsion. A great deal of
personal experimentation is the only way to succeed with gum. And you
have to be prepared for your prints to not be quite what you expected -
and accept the differences!!

Did you get that colour chart I sent you and was it any use??

Kate

Sandy,

Thanks for your advices.
I got some of he books you told me and they are helpful.
Do you know about other books on negative separation?
Yes, you are right I will only do it by computer but if you don't
understand
well the process then you won't be able to do it well.
For instance, I always have a print that requires an adjustment or
reprint.
How would you do it? Why it always happens with a specific print? Is it
the
pigment or is the specific negative layer?
By the way, when you reprint the cyan and you are following Sam Wang
paper
do you do it again on cyanotype? Not with gum?

Giovanni

----- Original Message -----
Wrom: QBGJSNBOHMKHJYFMYXOEAIJJPHSCRTNHGS
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, August 09, 2004 11:18 PM
Subject: Re: Gum dichromate issue

> There were more than a few full books put out on making separation
> negatives for the graphic arts. If you like I will try to provide you
> with full citations. I know there is at least one very good one in my
> university library and I suspect that if you do a search on a good
> public or university library in your country you will find the same.
>
> However, as someone who has actually made three-color carbon and
> carbon prints with film separations let me assure you that it takes
> a lot of time. There is no way in the world I would every think of
> doing that kind of work again without making digital separations on
> the computer.
>
> Sandy
>
>
>
>
> >
> >
> >> I do have several questions and probably too many but the first
is:
> >> Is there any book you recommend me to read that deals with the
three
> >> negatives instead of the Kodak single color negative?
> >
> >Good question. The best books on separation practice I recall were
short
> >things put out by Kodak that were out of print long ago. I'll look
through
> >my photo books and see what I can find. First, you have to separate
the
> >colors. Are you intending to make three in-camera negatives, or
shoot
> >color film (or digital) and do the separation later?
> >
> >The basic issues are (i) getting the color balance right, which is a
matter
> >of using the right filters and choosing the right exposure and
development
> >for the three negatives [with DT, one often develops the 3 negs to
> >different contrast levels -- I suspect the same may be true of other
> >processes]; and (ii) registration of the three [or four, with a
luminance
> >layer] negatives. In the old days, we punched holes in unexposed
film
and
> >used pin-registered film holders, enlarger negative holders, and
printing
> >frames throughout the process. Condit, the manufacturer of
> >pin-registration equipment, went out of business a few years ago. I
> >understand that shrinkage is a factor with multi-layer gum, so
registration
> >may be more of an issue for you than it is for DT printers.
> >
> >Best regards,
> >
> >etienne
>
>

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