Digital BW, The Print

Hello All,

Over a period of nine months I have periodically placed a small print,
with a portion of it covered by a 4-ply mat board strip, out on my
south-facing front porch in direct sunlight and kept a time log.  I
live in southeast Florida, which is in the sub-tropic latitudes, and
sunlight here is very intense even in winter.  I placed the print
outdoors only on days with few or no clouds.  Recently the direct
sunlight exposure passed the 100 hour mark and it seems like a good
time to post a report.

The print was made on VFA with a 2400 using K3/ABW, and the image was
sized to leave a 3/4" border.  The purpose of the test was twofold: to
test the lightfastness of the inks and any OBA-related changes of the
unprinted paper (hence the wide border).

The short report is that compared to the covered portion, there is no
visible change anywhere in the image, and a barely noticeable
lessening of brightness in the border.  The actual border difference
was measured by Steve Karafyllakis with a spectrophotometer, and the
numbers are below, but first there are some interesting side notes.

At first look there appeared to be noticeable yellowing in the border
(rather dingy looking, actually).  It turned out to be mostly a fine
coating of dirt, much of which brushed off.  As a further experiment I
washed one corner by holding it under running water for a few seconds
and rubbed it gently with a finger.  After drying, the difference
between it and the covered portion is barely noticeable.  You would
have to be looking for it to see it.  For all practical purposes there
is no significant change after 100 hours in direct sunlight.

Here are the numbers, each an average of three readings:

Covered border
--------------
L 97.99
A 1.49
B -1.81

Uncovered washed border 
-----------------------
L 97.62
A 1.21
B -1.04

Uncovered unwashed border 
-------------------------
L 97.10
A 1.17
B -0.96

Interpretation: L is brightness, A is the red/green axis and B is the
blue/yellow axis.  So the declining numbers mean that there is
lessening brightness with more red and yellow.  

I'm not conversant with the numbers, but visually the difference
between the covered and washed uncovered borders is barely noticeable.
 I doubt anyone would see it if it wasn't pointed out.  The unwashed
area looks dirty (yellowish brown) and AFAIC is irrelevent - it's just
dirt.

In the image itself (a landscape) there are no areas of any visible
difference.  Since it isn't a step wedge there is no consistent place
to take a spectro measurement. There are areas of pale sky and smooth
light to middle gray dunes, places where any changes would show first.

Now, the big question for me is what does 100 hours of direct Florida
sunlight translate to in some other relative value, such as Wilhelm
Years?  Wilhelm uses a test standard of 450 Lux @ 12 hrs/day to
represent a typical environment for displayed prints.  What does 100
hours of sunlight mean in those terms?  Ideas anyone?


Regards,
Clayton


Info on black and white digital printing at    
http://www.cjcom.net/digiprnarts.htm
I-Trak 2.1   http://www.cjcom.net/itrak.htm