Digital BW, The Print

> -----Original Message-----
> From: Paul Roark [mailto:paul.roark@verizon.net] 
> Sent: Sunday, August 31, 2003 11:43 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: RE: [Digital BW] EAM turns yellow!
> 
(snip earlier)
> 
> All I see in my testing is what I believe to be rather normal 
> "yellowing" of the optical brighteners, which is common with 
> all such brightened papers. EAM/EEM appears "normal" in this regard.
> 
> Note that in Jon's post he also observed, "Submitting silver 
> prints to accelerated light tests usually cracks their 
> surfaces anyway."  This makes me wonder about the test 
> conditions.  Are his test conditions cracking the
> surfaces of silver prints?   I have put silver prints in my 
> tester for short
> durations and never seen any surface cracking (also no fading).
> 
> Jon is using a Xenon lamp which I believe is very bright.  It 
> may be very hot also.  With an appropriate daylight filter, 
> it can put out a spectrum that is similar of daylight -- but 
> that may include UV that is beyond what my test samples are 
> exposed to.  If the Xenon lamp is being used with no filter, 
> I'm not sure what the UV content of the light is.
> 
(snip earlier)
 
Paul,

Very true and leads me to point out that one of the possible flaws in
"display life" of "fade" testing is that the test conditions may provide the
activation energy that would not be encountered in real life situations.
Chemical reactions occur at different rates. Some chemical reactions, like
the formation of a latent image on film, require an input of energy to get
things started. This is called activation energy and you can think of it as
the push need to get the ball rolling down hill. For some reactions the
activation energy is high and you have to push the ball over a small or
large hump before it starts to roll on its own.

I am concerned that while very bright light sources are needed to simulate
long years of exposure in testing prints, the high intensity may be
providing the activation energy to trigger reactions that would never occur
except under extraordinary conditions. The good side of this is that
anything that holds up under these torture tests is probably really good
materials to work with. On the other hand they may be giving the false
impression that other materials are inferior when they would actually be
fine under normal conditions. Impossible to say. So we need to continue the
comparative testing but keep referencing it to real world experience as time
goes on.

As to the cracking gelatin two things would have had to happen. One the
gelatin would have had to get very hard and two either the paper or the
gelatin layer dimensionally changed size. Like you I would guess heat but
the high intensity light alone might do it. I have boxes of old family
photos ranging from modern back into the 1880's. Almost all of them have
failed to stand the test of time but none of them show any signs of a
cracked gelatin layer. Even thinking of the faded, sun blasted color prints
in real estate office windows I have not seen this happen in real life.

So this is an excellent example of the fade testing results producing a
"false negative." If we did not know any different, we would be inclined to
rule out silver fiber as a choice for making photographs.

Martin Wesley
http://www.carolyn.cc/Guests/MartinWesley/pages/MW_01.html
http://www.borderless-photos.de/guests.html