From: Judy Seigel (jseigel@panix.com)
Date: 04/25/00-02:14:18 PM Z
On Tue, 25 Apr 2000 Smieglitz@aol.com wrote:
> This is the first test of a quartz halogen FEL lamp vs. UV flurescents
> that I ran a few months ago. The gum emulsion appears fogged, not
> overexposed, or longer scale, etc. It is just plain fogged. This is
> only a preliminary test, but it sure surprised me. Obviously much
> more testing is needed but the results here would indicate that the UV
> tubes are not an ideal source for gum printing. Halogen lamps appear
> to print cleaner, with better separation and contrast with respect to
> the gum emulsion. I'll be testing more now that the current school
> semester is ending.
>
Joe, re why your gums fog in the fluorescents, two questions come to mind:
What is your paper contact: Is it possible contact is less on the UV
table so light could creep under?
Do your UV bulbs have some kind of *reflector* system under or around
them?
How long are those exposures?
How do you define fogging (sorry I can't make it to URL just now).
Actually, I've never seen *fogging* in gum prints, that is, *veiling* on
the top steps of the 21-step -- tho some combos (usually involving the
size) don't CLEAR, or only with much mottling.
You may think a person who can't count to two isn't for real about
fogging, but I figure an extra question or so is all to the good in this
fascinating discussion. I'd hate for you to think I cast aspersions on
your fluorescent lights -- but I have taught HUNDREDS of space cadet
undergraduates gum printing under BL fluorescents and seen all kinds of
mis-and-malfeasance, but NEVER fogging from the UV lights. (Tho fogging
from drying by hairdryer until I caught them and made them read the
worksheet.)
But another question occurs -- how long are your soaks? And another -- as
I recall you use rabbitskin glue. Maybe that size doesn't like
fluorescent? Have you tried the tests on virgin paper?
PS. I have found time between exposures under half an hour not a
significant variable except in very hot humid weather -- but that may mean
you're using a negative of a photograph not a 21-step for the tests. In
which case the fogging could be because the neg is too thin. Not to
mention that those "tests" would refer only to a particular kind and range
of negative, with little objective meaning for users at large.
best,
Judy
> Before someone asks about controlling an infinity of variables in the
> test, let me say it is impossible to hold everything constant in a
> test of this nature. So the uncontrolled variable I chose was the
> time between exposures using the same negative. It was either that or
> introduce something else (e.g., paper coated at a different time,
> slightly different emulsion mixed at different times or the same
> emulsion sitting around and thus aged before the second exposure,
> different test negatives, etc.) I tried to match the maximum print
> density on the exposures and adjusted the distance/time of the FEL
> exposure to match the UV printer bank. I think the fogging is due to
> some elusive quality of the light source rather than the 7 minute lag
> between exposures. It might be due to some temperature effect caused
> by the sources heating the contact frame to different degrees, but I
> didn't notice any large difference (and also didn't measure for it
> either...next time).
>
> Joe
>
This archive was generated by hypermail 2b29 : 06/13/00-03:09:50 PM Z CST