The solution I found was to make three separate negatives: one with good
tones in the shadows, a second with good tones in the mid ranges and a third
with good tones in the highlights. Each negative is printed in registration
with the appropriate gum/pigment concentration. The shadows pigment is the
highest concentration of pigment with the shortest exposure. The midrange
negatives pigment concentration is one half that of the shadow concentration
and the higlight concentration is half of the midrange. The shadow negative
is printed first, then the midrange and finally the highlights. The exposure
times also vary with the shadow being the shortest and the highlight the
longest. If done correctly the print does not appear posterized but
continuous in tone.
Exposure times are long according to your standards. I use a bank of 4 UV
bulbs (I'm blocking on the number right now, but these are the standard UV
bulbs that fit in any flourscent fixture) and the shadow exposure is usually
3-5 minutes, midrange 7-10 minutes and the highlights around 20 minutes.
Never mind going out for coffee, I usually have something else to do entirely
when I'm exposing a gum print. I always thought that was one of the good
points to gum printing that is was a rather leisurely event. Something to do
while reading a good book or pondering the meaning of life. Although I must
say since I started reading this list several suggestions had lead to a
reduction in exposure times eg oversizing increases the need for exposure. I
guess I had the notion that if some size was good more size was better.
Larry