Re: UV Box Heat Fogging?

Seems to me I read about this in one of the issues of Post Factory. Maybe
I'll read it again. My light are only about an inch away from my paper maybe
this is too close. When I print longer maybe the problems become more
obvious.
I should have included this in the last post. This is how my "Red Green"
wedge printed out. I've exagerated the levels to show the oval in the orange
area in the upper left corner. That it's close to that magic pyro colour
should come as no surprise. Was there ever a "green" version of pyro?

http://www.mondotrasho.ca/pages/alt-photo/stepwedges/Red-Green-Printed.jpg

~m

----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, November 22, 2005 2:09 PM
Subject: 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 17:18:31 2005