Originally posted by Jay H:
"No test of fading potential could predict the results in any real-life situation."
What about testing in the real world?
Other than the percentage of blocked UV rays blocked, what claims have they made?
The blue "Textile Fading Cards" are color indicators, used to determine when fading has occured. And like all fading from light, the color indicators are purely subjective; accuracy depends on the viewer's ability to distinguish slight color differences.
You could see that one card is lighter than another, but could anybody say that one blue card is 20% lighter than another blue card? How could you be sure it isn't 15% lighter, or maybe 30% lighter?
For your own test, you could place those cards into frames with various glazings. Put all of the frames in exactly the same lighting conditions, at the same time, for exactly the same time period. Afterwards, compare the amount of fading on each card to the "control" card.
That would give you an idea of how the various glazing choices compare, in protecting
those cards from fading, relatively.
However, You would not be able to say one glazing is twice as good at reducing fading as another, because you wouldn't be able to determine that one card is exactly twice as blue as another card.
Also, the test would not give you any indication of how
any other item would fade in exactly the same light for exactly the same time.
And that is an important limitation. Any other item might react to the same light more than the cards did, or maybe less. There is no way to predict the results for real-world applications.
The folks who make and sell glazing for framing (not only glass, but acrylic, too) could not provide any fading information more useful than their products' ability to block a certain percentage of UV light. There is no other light-fading-related information to give; no other claim to make.
What other information do you think might be available & useful for framers?