glass
I doubt any place other than a frame shop or full-service glass supplier would have UV filtering glass you might 'accidentally' receive.
The architectural type is sold as laminated, and sold more for safety with secondary benefit of UV filtering (I think I had to tell the glass supplier when we put windows in our building what I wanted or guide their research because UV filtering wasn't a main concern in most of their installations). The laminate layer between the 2 lites of glass is what provides the UV filtering (about 99% but I can't tell you exactly what that means in spectral details off the top of my head, just that it compares to minimum 97% for conservation grade picture framing glass).
Non-UV filtering, 'regular' float glass (like hardware store window glass and non-UVF picture framing glass has roughly 43% UV filtering (same problem here, I can't remember the spectral definition that gives the 43% meaning). The green tint as viewed from the side I is from iron in the 'normal' glass recipe. 'Water-white (possibly a trade name) is low iron glass.
I cannot find a UV filtering spec for the non-conservation version of TruVue UltraClear (I think it's no longer sold, but the only product name I could remember). It can be hard to find UV filtering data for products not intended as UV filtering, but they all have varying degrees of it.
I don't think there is an advantage to the low-iron glass for contact printing, especially if you find a variety that only comes in a conservation grade (high UV filtering).
The green cast is annoying on some things, whites & pale colors, but most people only notice it when they're made aware of it, or are matching whites (mats and wall paint, etc. If it's that important we also compare mats under glass.) That isn't an indicator of UV filtering or transmission. UV filtering glass filters wavelengths shorter than 380 nm. UVF Acrylic starts at 400 nm (slightly higher into the blue-violet
range).
I was only able to find UV filtering/transmission information for non-conservation glazing for Tru-Vue glass and Ato-Haas acrylic. Tru-Vue may or may not even publish their non-conservation spectral data anymore...
'regular' acrylic (phone conversation with Ato-Haas polymer chemist) doesn't have a 'spec' for UV filtering because that's not what it's sold for, and may vary from mfr to mfr, but a ballpark figure is 70% UV filtering (not guaranteed). Unfortunately it's wavelength cutoff is different (spectrogram curve is very different not easily compared to glass).
But what I got from this was if I want maximum UV transmission, 'plain' glass was preferable to acrylic by a large margin, despite the apples vs oranges factor. Scratching is another deterrent. Not having found UV filtering (and implied transmission information) for 'waterwhite' glass, unsure where I can get it from my current suppliers, my belief the color cast negligible if any effect on UV transmission and the premium cost are reasons for me to not pursue low-iron/'waterwhite' glass for contact printing, especially alt-processes.
Visually, some things that may help you identify whether glass has intended UV filtering (but not assure you).
TruVue Conservation Clear has a UVF coating that can be seen if your eyesight cooperates, by looking at the reflection of a light bulb, then shift your focus from the lamp reflection to the glass surface, back & forth, while you slightly rock the glass. It's a rare and perceptive person who sees it without having it pointed out. If someone forgets to label the back of piece of framed artwork that required it with a Conservation Clear label, we check for the coating before automatically changing the glass unnecessarily. It's getting a little trickier for me to see as my eyes age, but I don't get 'false positives' I sometimes almost convince myself I'm looking at uncoated glass & try again. Once you eye is 'trained' its' easy to detect. I only know one customer since 1993 (an interior designer) who saw it on her own (& disliked the distracting character it imparted to reflections in her opinion).
Last ditch test is to take a razor blade or Xacto blade (not a glass cutter!) & try to gently scratch both surfaces of the glass (at an edge so you don't render it unusable for framing. The UVF coating on TV Conservation Clear will scratch, and the uncoated side generally won't. Maybe if you try hard enough you could.
DenGlas, probably no longer made, had a 'dip' coating that ran on the edges years ago. One would cut the edges off so they were not visible. I haven't seen enough of it to comment on it's reflectance or scratch properties.
Laminated UVF glass is for all practical purposes (maybe one could measure a difference in reflectance due to 6 surfaces vs 2) as clear as ordinary glass, but the center laminate layer can be seen from the side.
'Ordinary' vs UVF acrylic is indistinguishable to the eye. Can only be identified by trusting the factory paper coating's ID label (if not cut off when cut to size) or spectral testing.
While we have had suppliers send us wrong acrylic (both upgrade and downgrade), someone would have to be careless to accidentally give you a premium UV filtering product when you want 'regular'. The cost difference helps keep them from making that error.
Oh, TruVue's Anti-Reflective (AR) and Museum Glass have <1% reflectance compared to about 8% typical of most of their non-surface-treated (Perfect Vue Low Reflectance, if still made was about 4.6%), and AR used to be described at having 78% UVF (better than regular glass, but not a conservation product) and Museum has >97% UVF. If you move either around long enough while having a bright light source above or behind it, at certain angles you can see a pink or green reflection. (I have seen blue reflections in a local art museum but don't know whose glazing produt that is).
Too much info? (Maybe it's good for something else some day).
That's alright then. Tell me if I enjoyed them 
(I knew I would)
