Re: muddy gum print--help?
Charles, the first thing that strikes me is your gum mixture. If I understand correctly you mix your gum 1:1 with water. Are you mixing premixed liquid gum or gum powder? For gum bichromate I mix 1 part gum powder by volume to 2 parts water by volume. I then mix 1 part of this gum mixture with 1 part saturated pot dichromate and a small amount of pigment (tube w/c). Maybe your gum mixture is too heavy?
Jim
On Tue, Apr 14, 2009 at 3:10 PM, Charles Ryberg <cryberg@comcast.net> wrote:
Folks:
Thanks for the many helpful replies. I've split my answer in two
parts--one about non-VOC size and this one about color balance. This may be
more information than many of you want or need.
I use stock solutions of pigment. The basic mix is 5 grams in 60 cc of a
50-50 gum/water mix. That is, 30 cc gum, 30 cc water, 5 grams of watercolor
paint. When I recently bought Fabriano Artistic paper from Artarama I
noticed a watercolor paint labeled Lukas Process Magenta which I ordered and
have used in the posted examples. When I mixed this pigment at the above
concentration I got a very pale color--cheap paint, less pigment. I settled
at 15 grams in 60 cc. I won't use this paint after the tube is empty. It
is labeled PR122 but the print is small and I may have written some other
number previously.
When I was determining printing time and curves, the optimum mix was 3
droppers of my stock pigment, 2 of a 50/50 gum/water mix and 2 of saturated
potassium dichromate with an exposure of 2.5 minutes for cyan and 5 for
magenta. The yellow drove me mad as I kept needing to increase exposure
time--past 10 minutes. Thinking that ammonium dichromate was faster I
switched to ammonium for the yellow layer only and got a reasonable looking
curve at 5 minutes. The problem with these figures is that they gave me
VERY dark and muddy prints. I cut both the times and the concentrations by
10% then about 20% and got the image I posted--then carelessly ruined.
My attempt yesterday was to reproduce the ruined print and see if a fourth
layer of cyan would help as Sam suggested. Disobeying the fundamental rule
of one change per test, I also changed the printing order as suggested by
Joe. Parallel with this print--that is, coat both sheets with the same
batch of mix, expose sequentially, develop together--I did a print with
spray starch. I will write about that in my post on non-VOC size. Both
these images are now posted at http://ryberg.zoomshare.com/.
The new image is clearly way too magenta. There is pretty clear yellow in
the table cloth and the napkins are pretty clear white. I will soon add a
layer of cyan and, depending on the results, maybe a layer of yellow. If
there is any promise in the print, I'll reprint it with more yellow and less
magenta..
I'll worry about changing my triad of color when I get a print that isn't
yucky.
Thanks for your time and help. Charles Portland Oregon
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