From: Ed Stander (glassact@compuserve.com)
Date: 04/25/00-07:18:08 AM Z
Jeff:
I've run tests on several light sources using gum as the medium, and have
found the following:
Gum appears to respond best to frequencies 365 nm and below. Energy
above 385 nm is pretty well lost on the process. Thus, one can have a
wonderful bank of BL bulbs giving enormous amounts of UV in the 420 nm
range, and yet require long exposure times with gum.
Mercury metal halogen bulbs provide strong spikes in their output, one of
which is in the important 320-380 nm range. However, here we run into
problems with pigment absorption. Some pigments strongly absorb light at
the spike, making (once again) long exposures a necessity.
The best light source out there is the Sun - no question - although the
source does have a habit of not being user friendly. The Sun provides a
very wide band of UV light without major spikes, allowing the light to
effectively "get around" the pigment blockage.
The second best source is the mercury-iron metal halide bulb. The
addition of iron iodide in the bulb widens the UV output, and produces a
spectra similar to the Sun's. For an example of this - see www.olec.com,
and check out the spectra of their L-902 (mercury-iron) and L-900
(mercury) bulbs.
The L-902 type bulb requires a high energy input to get it going, and is
usually reserved for high end graphic arts lamps - such as the Violux and
Olec AL-913. The mercury bulb in the B&S oven is fine for Platinum, but
would suffer by comparison in gum applications. In other words - 400 watts
is nothing if it all goes to the wrong place!
A side issue with the Pizza Oven light box is the difficulty of using
same with a vacuum frame. These simply don't fit. Hope this helps! Ed.
P.S. - I still have one Violux unit to get rid of, as well as some 20x24
sheets of direct positive LPD4 film should anyone be interested (contact
me offline)..... E.
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