Re: UV Box Heat Fogging?

I'll suggest that the UV tubes give inconsistent results and random
fogging on occasion WITH GUM, IN MY EXPERIENCE. Since switching to a
quartz halogen lamp or mercury exposure unit, and using potassium
instead of ammonium dichromate, I have not since experienced any fogging
issues.

I don't know why this random fogging happens, but it does not appear to
be heat-related (although I'm positive excess heat could fog the gum
emulsion).

This fogging effect was also observed by Stephen Livick when he ran an
online class on the old Bostick & Sullivan forum, and I've had a couple
other people relate to me over the years they have observed the same
thing, but generally this observation is dismissed by others.

Here's a test I ran:
http://my.net-link.net/~jsmigiel/images/technical/UV_Q.jpg

Exposures were adjusted for both UV sources to produce maximum density
at an identical exposure time and both the UV box and contact frame were
cooled by a fan to help eliminate the heat variable.

Make of it what you will...

Joe

>>> mkochsch@shaw.ca 11/22/05 12:04 PM >>>
Does anyone (else) experience what I think is heat fogging during UV
exposure. I'm using an eepjon like box with GE BL tubes 15/20s. I was
doing
some max density tests on a new step wedge and started to double and
triple
my exposure to see how effective my negative was at blocking UV when I
started to notice two things. The first was edge bleed on squares which
should have printed clean. The second was a general fogging toward my
densest squares, or so I think. It could also be the color ranges I've
selected are not providing enough contrast and therefore I'm just not
able
to clearly define white. The thought occurred to me that once the
emulsion
starts sitting in the oven for 24 minutes instead of say six perhaps
heat
becomes an issue. Thx.

~m
Received on Tue Nov 22 15:23:45 2005