Does non-glare glass, used in picture framing, absorb or reflect UV rays and why or why not?
As the Master’s article says, glass absorbs most of the UV light. A normal anti-glare coating does not affect UV transmission. I’m not familiar with picture frame glass, but they may have additional coatings to absorb near-UV rays. Eyeglasses often do.
As I understand it, there are two ways to reduce glare, one is to add coatings to the glass’s surfaces to cut down on internal reflections (that is, when light enters the glass, some is reflected, and when that light exits the other side of the glass, some more is reflected, which is undesirable in some applications); this is used on camera lenses, telescopes, etc., to increase light transmission, including, presumably, UV rays. The other method is to etch the glass so that reflections are scattered, and I believe this is what’s done to picture-framing glass, so it shouldn’t increase UV absorption.
Disclaimer: I am not an expert; the above is just my opinion, though I believe it to be informed and (at lease mostly) correct.
I am appreciating the responses. I am a custom picture framer and somewhere in my past, I was told that non-glare glass absorbs ultra-violet let. Now, years later, I need to support that “fact”, and I see no literature concerning this.
I would like to be literate on this.
By the way, non glare picture framing glass is acid etched on one side.
I believe that the coatings on lenses only work for certain wavelengths; they consist of a very thin but precise layer of material; the light reflecting back from the bottom of the layer is out of phase with the light reflecting back from the surface and destructive interference occurs.
I believe the thickness of the layer is (usually) tuned to work best at the peak of the visible spectrum.
I was wrong to say that an anti-reflection coating does not affect UV transmission. Still, the difference should be extremely small. As Mangetout said, those coatings are optimized for visible light and not very effective for UV. And even if it were optimized for UV, an uncoated glass reflects about 4% so eliminating will increase the transmission by only 4%.
Anyway, apparently this is meaningless to the OP who was referring to etched glass. My understanding is that etching is a physical process and does not alter the chemical composition of the surface, so it should not change UV transmission. But as I said, it’s possible that the glass has a separate anti-UV coating added.
We seem to have skipped the question of what wavelength UV we are talking about. I guess it’s “whatever damages paintings” - does anyone know what that wavelength is?
According to Tru Vue’s Glass FAQ:
Reading through the rest of the FAQ, I didn’t see anything specifically about how etching glass affects its UV properties, though.
All of these answers are getting closer to my answer. I especially appreciate the one from Tru View. They are one of our suppliers and it was my plan to visit that website tonight.