> On June 5, Judy responded to my post:
>
> The resident expert at Voltarc told me they found exposure times
> just about the same with fluorescent bulbs at 415 and 360 nanometers,in
> platinum and other "non-silver" processes, but whether this sameness
>
> About the same? Meaning what, exactly. As you mentioned later, you desire to
> tweak in the process by matching negative to print material, etc. so why not
> tweak in the bulb, too? A good test would require that same wattage 360 and
> 420 bulbs be used in the same exposure unit so all the other poswsible
William -- The wavelength of the light and the "curve" of negative and
emulsion and match between them are two entirely different matters. In
the first place, no emulsion is sensitive at just one point. If you look
at the bar graphs you'll see spikes of sensitivity over perhaps as much
as 100 nanometers. When we say "platinum is sensitive at 415 nanometers"
we mean the greatest cluster or highest single spike is there. Ditto for
dichromates at 360. I haven't tested this, but apparently Voltarc had;
the man told me, in fact, that they found times "exactly" the same, but
I didn't think that important enough to claim.
Because what we're talking about here is only a minor difference in exposure
time -- or a POSSIBLE minor difference. If my times are 5 minutes, I
don't need to test in case another bulb would be 4 1/2 minutes.
Take even grow-light bulbs, which have their greatest
sensitivity somewhere else entirely. Even they will make a print if you
care to wait around long enough. Ditto photo floods, though the electricity
bill will break the bank. Etc.
But the properly matched negative is CRUCIAL for print quality, for best
density range & shadow & highlight separation.....unless you like cutting
masks.
> Yes, I did mean masks, but mine, placed on the surface of the glass, are far
> enough away from the image that a hard edge doesn't appear. Another trick is
> that after cutting the rubylith I take a red fine point Sharpie pen and draw
> a squiggly line if necessary to soften the edge. In fact, right now I'm
That red Sharpie line strikes me as very ingenious, but I confess I'm still
puzzled about the masks. What do you draw the fine
red line on? Clear acetate under the rubylith? I haven't tested that for
optical degradation, but would certainly be disinclined to cover my
negatives with it, even for gum ....And a stickler like you? (Talk about
NEANDERTHAL!)
>
> I was sort of joking with the neandrathal bit, but then just because gum
> isn't "exactly cutting edge" we shouldn't necessarily use techniques which,
> young or old, are potentially dangerous. When I made that comment, it was in
> reference to an earlier post where someone talked abiout sticking his hands
> in the light beam for dodging and burning and I still call that neandrathal.
> Maybe cro-magnum (sp?) but pretty silly nonetheless given the potential harm.
I don't remember that post, though I myself mentioned dodging & burning
-- but nothing about sticking my hands in the light! As for "potential
harm," see my post about sunbathing. Also, I can't help wondering how
many of you folks wringing your hands about UV bulbs are
SMOKERS ! ! ! ? ? ? ? ? ( And a few other even more dangerous practices
come to mind !)
Yours wholesomely, Judy