mark said:
...So I am wondering if there is a book/article/something out there that describes how to do this from three incamera negatives.
Any help would be nice.
Mark,
If you want to do this from in-camera negatives you'll need some tricolor filters and a static subject. The filters will all have different exposure factors and you will have to test development times for each color. I did this once with some success with wratten 29, 58 and 47B filters IIRC. It has been about 15 years but from memory the 47B flter negative had an exposure factor of 12X and received the most development, I think I gave the red filter 8x and the green 5x, and development was pretty standard for the latter two. You'll need a panchromatic film like TMAX 100 or 400 to pull this off.
If you are doing this for gum you don't want too much contrast in any of the negatives so they would appear to print flat with a #2 silver paper.
I'd recommend something like Daniel Smith New Gamboge for the yellow printer, maybe quinacridone rose for the magenta, and prussian blue for the cyan. This won't give you accurate color, but should give you an introduction. Alizarin crimson and phthalocyanine blues are usually recommended for the magenta and cyan pigments, but IME these colors are way more prone to staining than the ones I've mentioned (although all quinacridones do have a tendency to stain). Alizarin also isn't very permanent. Other yellows tend to more opaque which would be OK if you print them as the first layer but that complicates later registration. (Hard to see a yellow image through an orange emaulsion.)
Size the paper with a good gelatin and harden it in a formalin solution if you can obtain and handle it safely (avoid inhaling fumes, etc.) since it is carcinogenic and a respiratory irritant. Other hardeners work, but not as well.
The paper needs good wet strength and dimensional stability. Something like the old Fabriano Artistico would be my choice in 300# weight. Another good paper is Winsor and Newton 90#. Preshrinking will help.
I usually mix the gum:dichromate in the ratio of 2:1 and use saturated potassium dichromate as the sensitizer. Pigment strengths vary-you'll just have to test.
I'd read KOL for the section on 3-color printing but would not put any faith on the actual gum printing chapter. Crawford quotes Andersen's pigment:gum test which is invalid as far as I'm concerned and will only give you misleading info. Also, too much pigment won't cause stain, only underexposure and flaking contrary to what you may read in texts. A pigment is either going to stain or not depending on its composition and the paper. More pigment will cause a heavier stain if the pigment is a staining one, but with such a pigment, there will never be a point where some staining won't result.
Perhaps there are resources on the web dealing with making color separation negatives for processes like dye transfer or Evercolor. I'd spend my time investigating those rather than following some specific web gum recipe you might find because YMMV.
Joe
