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

[Christina Anderson]

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