Well, another day another crash at Panix. Back on-line 24 hours later I
see 15, 20, maybe 90 new messages on gum! After I get back from 150
Broadway (plan to pick up software for new provider!) I'll add my 2
cents, but here's what I had in mind when computer rejected me:
There was a question about the kinds of negatives best for gum and
continuing talk about dichromate dilution. The two affect each other.
The contrast range of a given coat of a gum print varies with
1.) the paper (amount of "tooth" to hold pigment)
2.) the gum-to-bichromate ratio (what will dissolve, what will harden)
3.) the bichromate concentration (sensitivity)
4.) development (length & temp of soak, whether "automatic" or forced).
Among other factors.
A test print made under a step tablet using proposed method lets you
count steps. Count real, usable steps, not faint differences. In the
shadows especially don't count a step unless there's enough difference
to carry shadow separation.
The number of steps printed -- seldom more than 5, often less -- is the
contrast range of your print with this mix, paper, development. (Notice I
don't say "this exposure", since NUMBER of steps rarely changes with
exposure, simply moves up or down the ladder.)
A density difference of .15 per step (as in 21-step Stouffer guide,
which I use) gives a total range of 7.5 density, and that's pretty much
the maximum. Whether to limit your negatives to this range, so as to get
everything in the negative in a single coat (or each coat if you're doing
multi-coats anyway), or whether to count on doing two or more separate
exposures, say shorter to hold the shadow separation, and then one or
several longer ones for highlights & midtones, is printer's choice
(theoretically, though I find the best-laid plans gang oft agley
[aglay?], to coin a phrase).
One determinant of course is whether you're using existing negatives or
making special flat FLAT ***FLAT*** negatives for gum.
And here is where the issue of bichromate dilution comes in. Although I
try to be a good citizen and use weaker bichromate, the stronger solution
is an important contrast control -- the stronger the sensitizer, the
greater the overall sensitivity, hence the more you hold those highlights.
However, inspired (goaded?) by Sam Wang's comments, I've been experimenting
with a brief flash. 5 units on a total exposure of 140 units was too much. (To
be continued.)
Yours before future crash .....
Judy