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Digital Negatives and Gum
As I continue explorations of gum printing from digital negatives I have
found and interesting observation. As I apply, expose and develop
additional coats of emulsion, the shadows and mid-tones gain density, but
the highlights do not. Same emulsion. Same exposure time. Same
developing method. The reflective density readings from the shadows went
up by about 30% from the first coat to the second (from 1.00 to 1.29) while
highlight values (as high as the 0.4 range) increased very little or not at
all! It makes me wonder if the second coat of emulsion is lifting out some
of the pigment from the first coat as it develops? This certainly will
make it more difficult to print a new negative for the second, third, etc.
emulsion layer to adjust the print 'on the fly' as the image is being built
up.
On another note, I've been playing with the spectral density of ink-jet
negatives (a la Burkholder). I've found that the density of the emulsion
should probably be calibrated for the specific emulsion used. Some of my
initial experiments used a light dose of lamp black pigment in the emulsion
and it looked like the C:0 M:71 Y:71 K:0 recommended in the book was in the
right range (100 printed black, 0 stayed white). I'm now trying to dial in
a curve for a heavy dose of lamp black pigment. I find that I must use
nearly 100% of all four inks (I'll probably cut back the density on C & K a
little,still working on it).
More food for thought for those with a digital mind.
Garet Denise
garet@rmi.net