Digital BW, The Print

JULIO FERNANDEZ wrote:



> Further to my earlier post I like to quote statements from Mr. Livick:
> IF YOU MULTIPLY THOSE FLUORESCENT RATINGS BY .33% IT 
> WILL REFLECT A MORE ACCURATE RATING FOR DAYLIGHT DISPLAY CONDITIONS WHEN USING ULTRACHROME
> TYPE OF INKS."

Does anyone *really* believe this? This quotation claims you have to 
multiply Wilhelm's figures by 0.0033 to get a realistic number. So a 100 
year Wilhelm-rated print life "really" would mean the print will last 
for four months before significantly fading.

I assume everyone here already has experience with their prints lasting 
that long or longer.


> I Expected that Wilhelm labs would be testing using high energy fluorescents but my 
> surprise they are not.  I made an assumption and I was wrong. Mr Livick is right.

It took me less than two minutes on Google to come up with this:

http://www.wilhelm-research.com/ep9600%20print%20permanence.html

where he speaks of his bulbs having emission at 313nm and 365nm. When 
speaking of optical emissions, this would be high energy indeed.

Granted, X-ray and gamma radiation would be even higher energy 
emissions, but I don't think anyone seriously believes that accelerated 
gamma radiation fade testing is relevant to this subject.

Here's my point: Wilhelm Research at least knows where its emission 
lines are. If you know where the emission line is, you probably know its 
flux as well. A few minutes looking around at Wilhelm Research's IST 
papers shows that their test assumptions and conditions are fairly well 
documented. They've done some experiments, they've published their 
results, and they've opened their findings to debate and criticism 
amongst other people who can do similar experiments and publish findings 
that support or conflict with Wilhelm's.

Livick, on the other hand, has apparently published nothing that has had 
peer review. As far as I can tell, his discussion of longevity does not 
appear to include *a single rigorous measurement* of anything - no 
measurement of flux, nor bandpass, nor even a colorimetric 
quantification of print color over time. He provides a few "lux" values 
using a standard camera meter in integrated light, so these 
"measurements" are very approximate and aren't correlated to passband. 
He doesn't use a photometer, he doesn't use passband filters, and he 
offers no UV flux measurements that I can find. The entire discussion is 
built upon a mathematical house of cards, in which "typical" room 
illumination is basically defined as X, outdoor exposure to direct 
sunlight is defined as Y, etc - from which we can multiply all this by N 
(for the number of months), and correct for Y (some nuance of display 
conditions), and firm conclusions are drawn from these extrapolations of 
assumed, unmeasured truths. All this is explained without formulae, 
without graphs - just text, riddled with misspellings at that. A big 
problem is, since important conditions are unmeasured, any small change 
to the function's inputs makes a BIG difference in the derived print 
lifetime. This doesn't strike me as good methodology. He mentions at 
some point that an Ultrachrome exposed to full outdoor sunlight will 
fade in quite a short time - which it will, but he doesn't explain how 
he controlled for other, non-light sources of fading. Etc. I could go on.

This doesn't mean Livick is wrong. I think he's probably right in 
several criticisms of Wilhelm's methods and in saying that Wilhelms' 
numbers can't be taken as absolutes. But Livick's results fall far short 
of providing the kind of data one would want to have if one really 
wanted to *know* how long their prints were going to last. Although we 
know Livick's methods are very imperfect, we don't know how imperfect 
they are. We have a much better idea how imperfect Wilhelm's methods 
are, and that makes their much more valuable.