Having on hand 4 kinds of gum arabic -- a sample from Photographer's
Formulary, the "Premier" gum from Daniel Smith, my old lithographer's
gum-14, and my new RBP gum, I was compelled by out-of-body forces to do a
comparison test, which in case you want to stop reading right now had few
conclusions.
Pigment was Rowney ultramarine blue, 1/2 gram to 40 drops gum & 80 drops
am di, heavier pigment to gum ratio than most multigummi printers use,
lighter than my usual.
Exposure was 100 units on the NuARc under a 21 step, development was 1
hour, papers included Strathmore Bristol drawing, Zerkal, Lana, Coventry
Rag, Hahnemuhl Merten Spiess, Copperplate, and litho cover, and a few
others lying around (yes it was an odd lot) with a couple of different
sizes as well as just the fresh paper, 101 samples in all (4 batches in
the NuArc).
The "best" gum on one paper wasn't on another, or the paper-gum combo with
the smoothest highlights wouldn't have the richest color or the one with
the cleanest whites on one paper would cling like glue on a different
one. And results, I assume, would jumble up again with a different color.
My plain old lithographer's gum was "best" in the fewest cases, but each
gum was best on at least one combination -- the other three were about a
tie, and you could adjust paper, size and mix to bring out the talents of
any of them. For instance, to make the tests consistent, I used my RBP
gum straight, though I generally dilute it with water; it would have done
much better "adjusted." The Daniel Smith Premier is *much* the lightest,
almost water white, but that may be what you pay $60 a gallon for. The RBP
was very dark, but you didn't see the difference in the dry print.
Given that the RBP gum is hard to get, I'd get the Photographer's
Formulary gum simply for availability and price (assuming it's still around
the $25 per gallon it was last year).
Is that perfectly clear?
Note also, this test was one part gum to 2 parts dichromate (chosen
because it gives the most staining). I assume things change again with 1
to 1, not to mention 2 to 1. I'm not going to test any other combos.
Whoever wishes to, I pass the baton...
Cheers,
Judy