From: Bob Kiss (bobkiss@caribsurf.com)
Date: 04/02/03-08:07:14 AM Z
DEAR SHANNON,
I think the problem is more hydrocarbons and other chemicals in the smog
than haze. We all learned the hard way that we could get a sunburn at the
beach on a hazy day just as quickly as a sunny one. The haze may scatter
the UV but it doesn't attenuate it much. The chemicals, which are present
to some extent on both sunny and hazy days attenuate the UV much more. I
used to lay on the roof of my building in Manhattan on a sunny day for an
hour at mid day and get very little tan but 15 minutes on my deck on Long
Island (no, not by the sea; no water or sand reflection) and I was a Krispy
Kritter.
I know that the wavelengths that cause sun burn (shorter) are not the
same as those that are actinic for iron processes (longer, I think) but they
are close enough that the process may be the same.
The photo-chemists on the list may be able to shed more light, as it
were, on this.
CHEERS!
BOB
----- Original Message -----
From: "Shannon Stoney" <sstoney@pdq.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, April 02, 2003 11:25 AM
Subject: RE: cyanotype exposure times
> Shelley wrote:
>
> >
> >I hadn't even thought of something like this!!!
> >I saw some of the other students yesterday, and their prints were
> >fine. They had also done them on bright, sunny clear days.
>
>
> Sometimes even when it LOOKS sunny, exposures can be inordinately
> long. Once I was making cyanotypes on a sunny day in Houston, and
> they were taking 20 minutes! At first I thought the glass might be
> UV resistant, as it was the first time I had used that frame, but
> then I tried my old tried and true frame, and it was the same.
> Apparently there can be haze filtering the UV light that we can't
> even see. This may be a bigger problem in Houston than in other
> places, though. I never had it happen in TN. There, my summer mid
> morning exposures were about three minutes.
>
> --shannon
>
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