Well hold the phone on that one (my emphasis added to Wm's comment), just
goes to show how we get so many of our "facts" in these processes (as in
life, too, of course, she said profoundly). Nobody in any mail I've gotten
has made a claim for cyanotype with cool white bulbs. I've been testing
just that & would have reported sooner except I'm having trouble with a
bad chemical (about which more under separate cover).
At the moment, though working with a bad emulsion, I'm getting a
reasonable blue and a few steps under the 21-step with the BL bulbs
(though requiring about twice my usual exposure time -- 6 minutes vs.
normal 3 minutes), but have not been able to get a SINGLE step in
cyanotype with the cool white bulbs-- which jibes with my long-ago tests
showing the cool white bulbs much MUCH slower on cyanotype than the black
lights. I'll post details of the system I've devised (not as "cyantific"
as Sandy's, but OK I think) and actual results shortly.
Meanwhile, two other points. The spectral-power distribution chart
of the *daylight* bulbs arrived from GE. It's not easy to read, as it's a
black and white photo copy made from a color original. Nevertheless, it's
quite apparent that about HALF the energy in this bulb is in the 400
to 500 nm range, the rest from 500 to about 650. The biggest "spike" is
at about 440 nm, with another at 400 and one at 550.
The BL bulb, on the other hand, has most of its energy at about 360, and
as well as I can read two differently conceived diagrams, possibly less
total radiation to begin with. Given our present assumptions about
broader sensitivity for these processes than we were raised to believe, it's
easy to imagine that the daylight bulb might be a *better* source for at
least some of them.
Which brings me to my other point -- I've made a few, so far screwily
inconclusive, tests of gum bichromate with the cool white bulbs. To date I
can only say definitely that *each color responds differently.* For
instance I didn't get any tone at all with normal 3 minute exposure on
burnt sienna with the cool white bulbs, but with a fugitive so-called
"process cyan" which I thought I would take this opportunity to get rid
of, I got about half the actual *number* of steps compared to the Black
Light, but the STEPS themselves (ie, the contrast) looked MUCH
better.(Help! This way lies madness!)
I would imagine, given the data above, that for all these processes the
Daylight bulbs would work better than the Cool White and possibly
better than the black light in a given set of conditions (apologies on
THAT one to Phil Davis, tho I stick to my guns on a couple others). The
possibility of changing bulbs to affect contrast certainly suggests
itself, though I imagine it would be easier to lay over a color filter, as
was apparently standard 19th century procedure. In any event, if I can
ever get through the snowbanks to a store -- well, first we'll get some
food, then a few daylight bulbs to try.
Judy