U of S | Mailing List Archive | alt-photo-process-l | Re: Yellow tents and UV (was: outdoor gum demo)

Re: Yellow tents and UV (was: outdoor gum demo)

Okay, I quoted that information, which came as a revelation to me,
from one skin cancer site, and I figured that the skin cancer people
should have a pretty good handle on UV. Since it corroborated my own
observation, that my gum exposures in sun don't change noticeably
from morning to afternoon, summer to winter, it made sense to me.
But it was only one piece of information, and so when challenged, as
I always do (wasting thousands of hours over the last ten years
checking out assertions made on this list) I looked further. There
doesn't seem to be a lot of available information on the subject, or
maybe I'm not thinking of the right google terms, but what I've
found is consistent with what I've already presented. Here's a
couple of samples:

"UVA rays persist all year round, even in the winter– unlike UVB
rays. UVA rays exist from sunrise to sunset, even on cloudy days –
unlike UVB rays. UVA rays pass through windows and glass - unlike UVB
rays." La Roche lab site

"There is relatively little fluctuation of UVA throughout the day and
in different seasons of the year." Photodermatology, Osterwalder and

Some of what I found doesn't look at UVA by itself but as a measure
of its relative proportion to the total radiation, which varies in a
way that would be wholly consonant with UVA staying fairly constant
while UVB fluctuates: UVA is a much higher proportion of radiation
in morning and evening hours, on cloudy days, and in winter, than at
midday and in summer.


On Apr 21, 2009, at 11:06 PM, Paul Viapiano wrote:


I observe this with pure palladium printing...7 minutes is my time.

Now, it's purely anecdotal and not scientific because I don't
measure reflective densities of wedges with a densitometer.


----- Original Message ----- From: "Loris Medici"
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, April 21, 2009 10:22 PM
Subject: Re: Yellow tents and UV (was: outdoor gum demo)

Which process is that and what was the exposure time? I did notice a
difference (albeit not linear as I first predicted - have to work
on this)
with traditional cyanotypes. Maybe it's because at fast printing
times it
could be harder to notice any difference and/or self masking plays a
significant role... ???

Anyway, I'm ready to eat my assertion (and go to the corner on one
leg) if
someone comes up with an quantitative explanation to why giving
the same
source (the sun) UVA intensity remains the same whereas other
types of
irradiation seems to change intensity.


22 Nisan 2009, Çarşamba, 5:36 am tarihinde, Paul Viapiano yazmış:

Remember when we were talking a little bit re: this on the Hybrid

So far, I've noticed no change in exposure times from UV Index 4
index 9 when exposing via the sun...