From: Judy Seigel (jseigel@panix.com)
Date: 06/19/01-01:01:55 PM Z
> There are BL and BLB. BL stands for BLACK LIGHT and the BLB for BLACK LIGHT
> BLUE. BLB lamps have a blue-violet coating inside and therefore block a lot
> of the visible spectrum.
Exactly.
But this thread is the perfect illustration of good and bad from "the
net," warping, misconstruing, needlessly complicating and generally
bollixing up what is actually quite simple.
I have tested most "alt" media under several lights, although not each
under EVERY light. Still the similarities are greater than the
differences, and the thing now looks to be getting out of hand....
The so-called "aquarium" lights are the AQA bulbs, and are liked for pt/pd
because the output supposedly peaks at 414 nm, pt-pd's greatest
sensitivity. But there are always other spikes down the line and different
mixes have different precise sensitivities anyway, so the practical
difference between those bulbs and regular BLs is dubious. I myself found
NO difference in use in other media.
Again, although processes such as gum nominally peak at 360 nm (which is
claimed highest output of the BL bulbs), depending on the color of the
pigment and the mix there are other spikes as well. The distinction if any
in use is trivial.
Similarly for the "metal halide" bulbs. Or at least the metal halide bulb
I tested with for 10 years. There were differences between it and the
fluorescents, but they were not as great as differences caused by emulsion
mixes and they were not consistent along the line. There's also the fact
that your cover glass is a factor in the equation, so any "rule" may well
work only with that glass. And the other fact that one adjusts one's
emulsion and exposure to fit the light source, which further irons out
differences, if any.
The BLB bulb incidentally, gives EXACTLY the same output as the BL, but
the (expensive) glass it's sheathed in permits only a narrow wavelength to
pass, so things get that glow in the disco. It will print whatever, but
with less light is simply slower about it, and lacking some other spikes
is probably a different "curve" --- maybe. But again, other factors and
ingredients affect that curve, too.
There is however strong testimony that the superactinic fluorescents (see
P-F Sources & Services) give not only greater speed but "nicer" contrast
for pt/pd, or so several users have testified.
PS. As noted there are a couple of new -- and old -- setups in P-F #6.
But there's no reason anyone should spend more than say, $150 and half a
day to build a light table... Unless you're trying to avoid photography.
Judy
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| World Journal of Post-Factory Photography > "HOW-TO and WHY"
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