Actually I've read that before about "straight line of
dichromates" (maybe from you?) but didn't think to apply it to
flashing...assuming it does apply. Is that a source I
could (A) find, (B) bear to read, and (C) understand? (I hope not!)
Assuming it's true, surely it would apply to carbon and related transfer
techniques more than gum.
I don't have a reflection densitometer, but the scale of gum
is so short it would be hard to plot, the whole range being little more
than a shadow step, a midtone or two and a highlight -- not exactly a
grand sweep. However, I have folders full of gum
tests printed under a 21-step guide, most of which show definite
shouldering in the dark tones, that is, anywhere from one to
four teeny tiny baby shadow steps -- discernible, but not useful.
(Cyanotype also shows definite shouldering, quite treacherous in
fact because of the humongous dry-down.)
As for the "toe," my sense in both cyanotype and gum is that the
highlights seem more a factor of the mechanics of printing than inherent
sensitometric law -- variables (in addition to the negative of course)
including paper, age and condition of emulsion, and, in gum, time
and type of development. With both media, some papers are like dropping
off a cliff at the high tones, others trail off daintily, delicately.
As for the particular subject of flashing -- I have
had EXCELLENT results with PRECISELY TIMED flashing of cyanotype.
The two too-flashed gum prints I mentioned, while NG as prints, allow
me to hope that on
that paper at least (a rag-content typing paper, BTW), flash will work.
I also note that my utmost serious attempts to lower contrast with
lith film (silver!) by flashing failed dismally. The flash changed everything
about the same. Slope didn't change.
In any event, I appreciate the comment, and this discussion does
remind me to also try a flash through the back!
More to follow.......
Judy