Re: separations for gum printing
P.S. I went back and reviewed all my information about curves; it's interesting to note that only these particular (rather intense) mixtures for tricolor have that particular shape. Less concentrated mixtures of the same pigments yield curves that are very close to the straight diagonal line. I think I said this somewhere else in the last few days, but what I found in my exploration of curves for gum is that the curve shape seems to be related largely to the pigment mix (not absolute pigment concentration, but the color saturation relative to that particular pigment) rather than to the hue range.
At any rate, the steepness of the curve at the dark end of those particular curves for those particular tricolor mixes seems to serve the tricolor print well, promoting good open separation in the shadows, and I don't see any particular reason to fret about it.
One correction: I said thalo was the cyan pigment in that group that I provided the curves for; actually it was Prussian. I can't find a curve for thalo, and am not sure I've ever done any calibration for thalo. It's not my favorite blue pigment for tricolor.
On Nov 20, 2008, at 1:00 PM, Katharine Thayer wrote:
Unlikely, Mark, on either point: overexposure (since my exposures for these were well established by step tablet, as explained in a separate thread and on my website page covering exposure for gum, and besides, by any objective criteria a 2-minute exposure with a photoflood bulb is unlikely on the face of it to be overexposed) or too dense a negative (since my negatives are so thin I have to put something white behind them to tell even what the image is, and the color I use for the negatives, determined using Michael Koch- Schulte's RNP Arrays, seems to work very well). I showed one of these negatives a couple weeks ago for someone who was interested in what film I use for my negatives; it might be useful to show it here.