How to tell if glass is tempered.

What am I doing wrong here? I have tried this over and over, and I don't see anything, just looks totally clear. I even tried my car side-window and saw nothing, so I must be doing something wrong.

I tried my laptop, and also my iPhone. Held it tight up against the glass and looked through the glass at the phone screen, whilst wearing polarized sunglasses and even 3D glasses. Whatever I try I don't see anything, can anyone tell me what I'm doing wrong. What am I meant to see? The pictures in that article aren't clear. If its not tempered is it meant to go black?


Are you turning the video or turning your head. You want to turn one or both until the screen goes black. If it's solid black, it's not tempered. If there are streaks of white, it's tempered.
 
Thanks

I tried it again this morning.

Without looking through any glass, tilting my glasses and the laptop screen, I still cant get the screen to go completely black, I can see when it gets brighter one way and much darker the other way.

So I went ahead and tested the glass anyway, and looking through the sides and back glass, it looks just like it looks without any glass. and I could tell the bottom was tempered as there were very dark streaks.

So I'm pretty sure that the back is not tempered after this test. Just curious to why I couldn't get the screen to go completely black?
 
I was able to use the 3d glasses method and see that my 240g 8' long front and back was tempered but when i checked the bottom it wasn't has anyone run into this before?
I would think on a 240g the bottom would be but it wasn't, do you think its safe to drill the bottom? or will that weaken the tank since its on the bottom and has to hold so much weight?
 
I would haul the tank to a professional glass fabricator, and have the glass checked with the proper equipment, before you even consider drilling the bottom of this tank. You either have a false positive on the sides, or a false negative on the bottom--or due to the unreliability of home brewed "tests," it may be just as it appears. But it does not make sense, for the sides to be tempered, and the bottom not.
 
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