I’ve got some posters that are matted and under glass. However, I don’t know if the glass has anti-ultraviolet light properties and I don’t want to display them until I’m sure they’re safe. Is there a way I can test with household items?
Is it real glass?
Then it blocks most UV.
Standard window glass, according to the International Ultraviolet Association, will allow UV-A to pass through while almost 100% of the UV-B and UV-C light is blocked. Therefore, some UV light will enter your home and potentially affect your skin. Some of these effects could include increased freckles and increased sensitivity to sunlight that could result in rashes such as photodermatitis.
UV b causes quick damage, but yes UV A will allow long term damage.
The Master Speaks- Can you tan through glass? - The Straight Dope
To summarize briefly: some ultraviolet rays can pass through car window glass, although most of the burning (as opposed to tanning) rays can’t. On the other hand, most sunlamps aren’t made of ordinary glass–they’re made of quartz or special UV-transparent glass…Having thus confronted our ignorance, let us humbly endeavor to learn. Ultraviolet light, which causes both erythema (sunburn) and tanning, ranges in wavelength from 4,000 angstrom units (A) down to about 100 A. (Light with wavelength greater than 4,000 A lies in the visible spectrum.) The most potent rays for burning and tanning lie in the 2,900-3,050-A range, with radiation of 2,967 A supposedly being most effective of all.
Ordinary window glass, however, is pretty much opaque to wavelengths below 3,000 A. From this we deduce that the intervention of a window will significantly reduce but not halt the burning/tanning process.
In addition, UV rays above 3,200 A will cause tanning (but usually not burning) if administered in sufficiently massive doses, such as you get when you’re driving across the desert. Your tan, therefore, was no hallucination. This business about your innate wisdom I’m not so sure about.
Newer US currency has UV-fluorescent fibers that will glow when exposed to UV radiation. I guess you could take the glass outside on a sunny day and see if the fibers still glow when behind the glass.
Know any reptile owners? Many use meters to detect how much UV light their bulbs are emitting (they emit less as they age, and need replaced). Maybe borrow one from a reptile owner or pet shop.
There’s a lot more to conservation glass than ‘any old pane’s ok.’
That’s a good idea except it’s difficult to see things fluoresce in direct sunlight. But it may work on a somewhat more cloudy day?
This is one I’d have never thought of, thanks. I don’t think I know anyone that has reptiles but I’ll keep it in mind.
Yes, if it is not actually glass, then I dont know.
You could buy a UV flashlight Combined with some US currency you’d have a good way to test glass for UV transmission.
I have two UV flashlights, though not this model, that we use for various purposes.
You’re unlikely to be able to tell with household items though.
Don’t take them into a motel room. You’ll regret it.
We don’t travel much, but have used them for that. 
My wife is a cashier at a local thrift shop, hers is used mostly for checking for fake bills.
My glasses darken in UV light. But I notice they don’t work well when the sun shines through my car windshield, which blocks a lot of UV. So maybe a pair of these type of glasses would easily indicate the level of UV coming through a piece of glass? But some do also react to other bands of light.