From: Sarah Van Keuren (svk@steuber.com)
Date: 04/25/00-09:04:41 PM Z
Finding this discussion of interest, I forwarded some of it to Jon Edwards
who makes the exposure unit mentioned by Darryl Baird: "I'd used an
> Edwards Engineering box successfully for some prints in V.D, cyanotype
> (original and Ware formulas), platinum, and gum. Of all of these gum was
> the worst."
Jon Edwards replied :
My units have been specifically designed for the Pt/Pd process, but over the
years a number of people have purchased my units for various alternative
processes, and they have used them successfully as far as I know. I have
talked to a hand full of people who have used my units for gum, and
generally
I get the impression that their exposure times are in the 20-30-40 minute
range.
My units use the BL tubes which have a wavelength peak at 350 nm
(nanometers)
and range from 320 to 380 nm. The BLB tubes shifts the wavelengths down to
the 280-320 range. The quartz halogen lamps shifts the wavelengths upwards
to larger numbers because it contains a lot of white light. The metal
Halide
lamps uses mercury, which has a sub-alpha peak at 400 nm and the rest of the
lamps radian is scattered in the 500-600 nm range.
Based on what was said in the discussions about quartz halogen and metal
halide results, the best ranges for the gum appear to be in the 400-500 nm
wavelength range. I think each alternative process will have its own unique
optima wavelength. Unfortunately there is no, or little, hard scientific
studies on these processes to isolate the best wavelength for a particular
coating process.
One thing that makes it difficult to "ferret" out good information from
these
discussion groups is the nature of light itself. If you have the correct
wavelength, and that a big assumption, generally exposure times vary
(almost)
directly with the intensity of the light. However, light intensity varies
with the inverse square of the distance from the source. And, distance is
the one BIG thing most people leave out of their discussions If a light
source is 2" from your negative and you get a 10 minute exposure, move the
light 4" from you negative and you will get a 40 minutes exposure, or four
times the time. You doubled the distance and reduced the light by 1/4th.
Then, add the variables of a 1000 watt halide at 14" and a 500 watt halogen
at 6," and 20 watt fluorescent tube at 2" to the equation, all with
different
wavelengths, and it really becomes confusing.
So, I cannot offer you any real conclusions about the gum process (only my
two cents worth) unless we have more information (e.g., type, lamp age,
wattage, distance, negative density, chemistry contrast, and exposure times)
from everyone offering their results, both good and bad. These are the data
most good printers should be recording when they print, so let's see if you
can shake it out of them? Then we can compare apples to apples.
Best regards,
Jon Edwards
Edwards Engineered Products
http://www.EEPJON.com
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