# non-glare glass **URL:** \ **Category:** Factual Questions\ **Created:** [March 14, 2003, 3:33am UTC](https://boards.straightdope.com/t/non-glare-glass/161251 "2003-03-14T03:33:39Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![PurplePerson](https://avatars.discourse-cdn.com/v4/letter/p/ec9cab/32.png) [@PurplePerson](https://boards.straightdope.com/u/PurplePerson)\ **Post date:** [March 14, 2003, 3:33am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/1 "2003-03-14T03:33:39Z")
Does non-glare glass, used in picture framing, absorb or reflect UV rays and why or why not? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 14, 2003, 3:38am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/2 "2003-03-14T03:38:08Z")
As the [Master’s article](http://www.straightdope.com/classics/a1_163b.html) 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. ---
**Author:** ![Earthling](https://avatars.discourse-cdn.com/v4/letter/e/90db22/32.png) [@Earthling](https://boards.straightdope.com/u/Earthling)\ **Post date:** [March 14, 2003, 8:18am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/3 "2003-03-14T08:18:37Z")
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. ---
**Author:** ![PurplePerson](https://avatars.discourse-cdn.com/v4/letter/p/ec9cab/32.png) [@PurplePerson](https://boards.straightdope.com/u/PurplePerson)\ **Post date:** [March 14, 2003, 11:48am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/4 "2003-03-14T11:48:58Z")
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. ---
**Author:** ![PurplePerson](https://avatars.discourse-cdn.com/v4/letter/p/ec9cab/32.png) [@PurplePerson](https://boards.straightdope.com/u/PurplePerson)\ **Post date:** [March 14, 2003, 11:56am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/5 "2003-03-14T11:56:04Z")
By the way, non glare picture framing glass is acid etched on one side. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 14, 2003, 12:04pm UTC](https://boards.straightdope.com/t/non-glare-glass/161251/6 "2003-03-14T12:04:05Z")
> [@](#): > > \*Originally posted by Earthling \* > **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** 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. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 14, 2003, 12:59pm UTC](https://boards.straightdope.com/t/non-glare-glass/161251/7 "2003-03-14T12:59:12Z")
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? ---
**Author:** ![Earthling](https://avatars.discourse-cdn.com/v4/letter/e/90db22/32.png) [@Earthling](https://boards.straightdope.com/u/Earthling)\ **Post date:** [March 14, 2003, 5:59pm UTC](https://boards.straightdope.com/t/non-glare-glass/161251/8 "2003-03-14T17:59:17Z")
> [@](#): > > \*Originally posted by scr4 \* > **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](http://www.tru-vue.com/primary_frameset.asp)’s Glass FAQ: > [@](#): > > The UV region of the electromagnetic spectrum ranges from 200-400 nanometers. The earth’s atmosphere blocks the light waves under 300nm, therefore they are of lesser concern. The shorter the wavelength, the more potential damage it can cause. Thus, light waves close to 300nm cause more damage than those closer to 400nm. Museum and conservation professionals and framing industry organizations like FACTS recommend UV blocking levels at a minimum of 97% filtration in the 300-380 nanometer range. Reading through the rest of the FAQ, I didn’t see anything specifically about how etching glass affects its UV properties, though. ---
**Author:** ![PurplePerson](https://avatars.discourse-cdn.com/v4/letter/p/ec9cab/32.png) [@PurplePerson](https://boards.straightdope.com/u/PurplePerson)\ **Post date:** [March 15, 2003, 1:45am UTC](https://boards.straightdope.com/t/non-glare-glass/161251/9 "2003-03-15T01:45:33Z")
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.