From: Judy Seigel (jseigel@panix.com)
Date: 02/13/02-09:26:14 PM Z
Not being a tennis player, I'm not sure about "serve," or if it's a good
thing & you want to do it. I hope so. However, here's another metaphor:
"God (or the devil) is in the details."
Cactus Cowboy wrote [Feb 8/02]:
> "... most gum printers will agree that too much pigment in the mix will
> create an undesirable stain."
If so (which I doubt), they're wrong -- in which case this info might help
them too: With the right gum on gelatin-sized paper (as I've said often,
in case you were paying attention), pigment stain hardly happens. Even
with twice the pigment, even with so much pigment the emulsion flakes off,
it hardly happens. If the paint works for gum bichromate (no troublesome
additives, for one thing), and the gum works with the combo, pigment stain
is a non-problem. But that Varn gum Dave uses (or used last year) might
be his problem. I tried the Varn against 5 other gums & found it by far
the heaviest stainer (at least in that particular combination.
To compare gums requires measuring very small amounts of pigment, &
probably impossible to get them identical with a normal lab scale. Making
up large batches for just a test strip or two is wasteful -- and even then
no assurance of perfect identicality. What worked was mixing a half gram
of paint with 30 drops distilled water (or whatever amounts needed), then
you can take up identical measures of pigment by dropper for the entire
series. (I nearly always add water to gum emulsion anyway, so the
character remains the same.)
In this test (August 16, 2001), I used Winsor Newton lamp black on Merten
Spiesse (Hahnemuhl) paper, pre-shrunk, gelatin sized and hardened. The mix
was 5 drops of the lamp-black-in-water, 5 drops of the gum arabic, and 5
drops 26% ammonium dichromate. Exposure was 3-1/2 minutes by BL
fluorescent, development 1 hour face down in tap water.
It turned out that three of the gums tied for best: Daniel Smith
lithographer's gum ($16.95/gallon, bought circa '99), RBP gum (now sold by
Philben, I'm told, about the same price), and Philben's former house gum.
All had roughly the same number of steps (6 or 7) and NO STAINING at all
(perfect paper whites !!). These happen to be my usual gums. The price is
purely coincidental -- they've been consistently best. Daniel Smith
"premium grade gum" (about $30 per pint when I bought it, or $60/litre, or
$240/gallon) stained and flaked and lacked highlight steps. Winsor Newton
gum arabic, $8 per 75 ccs (that's the water-white gum, about $420/gallon
!!), had 7 nice steps, but the paper stained gray, no clean white at all
(although it has been best with other combos).
Varn, $28/gallon from G.E Richards Graphic Supplies, not only stained much
more than all others, it had almost no steps, just one grainy gray step,
with solid black below that.
And speaking of "most gum printers," here's a higher authority from
Anderson's day. Franklin I. Jordan, FRPS, who also wrote a book,
"Photographic Control Processes" (1937), says "the amount of gum that the
mixture may contain is limited by the fact that with an excessive amount
it is difficult to blend the coating smoothly, and that an excess of
either gum or pigment may flake off during development." Note: no mention
of pigment stain.
Other writers said the same thing, but Jordan was major honcho. So why
didn't Henney & Dudley, Crawford, et al, reprint *that* instead of the
great G-P-R test? Well might you ask. I will surmise later.
Meanwhile, Cactus Cowboy ALSO declared, "the very notion of a measured
gum/pigment ratio is meaningless to you." ("You" here meaning *me.*) Sigh.
Yes, it's meaningless -- because it IS meaningless, being, as I've said
and said, based on an utterly erroneous notion. Which has apparently led
him astray, hung him up on "gum-pigment ratio" in short, looking for
answers where they aren't.
Of course, results in test above could vary with other dichromate and/or
other colors, papers, development, water, etc. (I meant to try variations
with the Varn, didn't yet.) However, my point is NOT which gum or pigment
or dichromate is "best," merely that stain is absolutely NOT a given.
If you'd like, Dave, I'm happy to send you some RBP gum to try. This
season's lithographer's gum at Daniel Smith is no doubt a different crop
from mine. That was a year of drought, which may have made the gum
especially dark, but it worked so well I got two gallons more from same
batch number.
best,
Judy
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