Summer, when the living is easy, must be the time for testing gum arabic
solutions. I have just finished testing the following different gum solutions
(all were labelled 14x Baume):
1. lithographer's gum ( brand name "Varn" sold thru Arvey)
2. Winsor Newton
3. Daniel Smith Premium Gum
4. RBP (gratefully given to me by Judy)
5. Photorgrapher's Formulary
All prints were made on the same paper: Fabriano Artistico cold press 140,
double sized in Knox's gelatin (4 pkgs/liter) and then hardened in (glyoxyl
25cc/liter).
The gum pigment solutions were all made with Rowney's Jet Black Gouache at a
concentration of 1 gm/5cc of gum solution. The sensitizer was a 30% solution
of ammonium dichromate. Equal parts of gum/pigment and sensitizer were used
(30 drops of each). The mixture was applied to the paper with a foam brush
and smoothed with an elephant brush.
The same test negative was used for all prints and a Kodak step wedge was
printed along side the negative. The exposure was 8 minutes under UV lights
(4 - 48 inch GE F40 BL bulbs). The negative used had a density range of 1.1
which is slightly higher than I usually use for gum printing but I wanted to
see the limits of changing the gum solution.
The prints were immediately developed in water between 90-100xF for still
development for 1 hour ( the water was changed once after 5 minutes).
Results:
The most important result was that all the prints looked significantly
different. The lithographers gum gave a "high contrast" look, with little
deposition of the pigment in the high light areas. Daniel Smith placed a bit
more pigment into the high lights while Winsor Newton placed even more
pigmernt and could be considered a "normal" contrast. RBP and Photographer's
Formulary (here after called PF) gave down right low contrast prints. It is
possible that what is happening is that the speed of the emulsion is changing
with each different gum solution and perhaps if the exposure time was
shortened that each pigment/gum/sensitizer mixture could be made to look like
one another.
However, when the step wedges are looked at some interesting data is seen:
darkest gray lightest gray white
range
Litho gum 5 8
9 6
Daniel Smith 5 9
10 7
Winsor Newton 5 9
10 7
RBP 6 10
11 7
PF 6 11
12 8
The numbers are those of the individual steps on the wedge. The pigment
density below that of the darkest gray all appear equal. Zone terminology is
a doesn't quite fit because the greatest density range is only 8 steps. I
believe the step wedge data confirms the overall impression of the prints.
The Litho gum has the shortest scale while the PF has the longest. Daniel
Smith and Winsor Newton gum give about the same look as do RBP and PF. All
the prints look the same in the shadow areas with considerable loss of
detail. If the exposure had been shorter I would predict that there would
have been better shadow detail but less detail in the high light areas. I
will make another set of test prints to see if this is the case.
It must be noted that none of the test prints appear "finished". All could
have been improved by multiple coatings and exposures. These were one coat
gums done to demonstrate the differences in a single variable.
Another note I did try a prolonged development time (8 hours) on an RBP "low
contrast" print to see if extended development would increase the contrast.
It did not both the step wedge data and the overall appearance of the print
were unchanged.
Overall, I would have to say that I agree with Judy that PF's is the
preferred gum solution because of it has the longest scale is less expensive
than DS or WN and easier to get than RBP.
Larry Shapiro