[Alt-photo] Re: GUM: problematic yellow?

[Luciano Teghillo]

Chris,

Thanks so much! I think it says it all. I hope to be posting my first effort
shortly.

All the best,
Luciano




-----Original Message-----
From: alt-photo-process-list-bounces at lists.altphotolist.org
[mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of
Christina Anderson
Sent: Thursday, February 06, 2014 7:01 PM
To: alt-photo-process-list at lists.altphotolist.org
Subject: [Alt-photo] Re: GUM: problematic yellow?

OK one last post for the day as I sit here avoiding writing my annual review
in 28 below zero weather this morning...avoiding going outside as well!

Luciano, I use a 3880 printer which is plenty dense for a gum negative. I
don't know how it compares to a 2880. I think my bulb set up is like yours.

Yellow is the hardest color to judge exposure on, because you can expose for
an hour and the brown of the dichromate becomes darker and darker brown long
after the layer of gum is suitably hardened. It gives a false read to the
step wedge since that dark brown is so visible through the light yellow.
Actually dichromate stain can give a false read of needing longer and longer
exposure to all colors, but with yellow it turns it a sickly green/brown.

You want to expose only until the gum layer is hardened and two steps are
blocked up and before much dichromate stain sets in. The only way to really
evaluate that is to clear the step wedges in potassium metabisulfite to fade
that stain since in the beginning you are going to have to overexpose to
merge the steps. That would be the complex way.

What I have done, contrary to all other processes where I do calibrate an
exact standard printing time because they are all "one shot" processes
(either you get it right or you don't, not a lot of wiggle room that gum
has) is with gum I do a step wedge exposure, grossly overexposing (15
minutes). Then I develop AND clear the step wedges. Then I evaluate where
the gum layer is hardened sufficiently firmly (by taking a brush and trying
to draw a line through the step when wet). Then I choose a suitable common
time within reason for all three colors and develop a curve for each color
based on that time. I use 10 or 15% am dichromate.

Now for the simple way. When I teach workshops and my class at MSU I use a
simple gum curve outlined in my article at alternativephotography.com (the
10/80 curve) and to prove it works, I used it for a couple years. I just
cannot teach a complex curve process along with gum and casein in a 6 day
workshop nor do most workshop attendants want to spend that kind of
uncreative/technical time. Susan Faye, Stella Schneider, John Howington,
Harlan Chapman, (Mary Donato may use something more complex) and all my
student work in the gum book is done with this very simple method. If the
students want to calibrate curves for the colors, they have that choice on
their own time.

And there are gummists who do not use any curves and do gorgeous work, too. 

And then gummists who use complex curves and do gorgeous work.

Gum is beautifully and infinitely variable and forgiving.

The issue is this: You can get a perfect time for each color and develop a
perfect curve for each color but when you print the colors on top of one
another with a tonal palette or a step wedge or some sort of thing (it'd
have to be a digital step curved with your curves) and seek neutral grey to
black, the layer order adds another variable that may change everything
because the paper gets more slick with gum. It's actually a very fun
exercise to do. Some colors will dominate in the midtones and highlights and
give a sort of opalescent effect. I think that is why gum is so intriguing.

Hope this long ramble helps in some way.
Chris

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