Tempered Glass

[RNall]

I didn't want to hijack any of the other drilling threads. I am in the market for a dirt cheap used glass sump. I'm setting myself up to find a great deal on an unknown glass tank with or without tempered glass. I would hate to get eveything set up and then shatter the glass during drilling.

I understood tempered glass identification was tricky at best and you still stood a big chance of finding out the hartd way.

I read somewhere that light passes through tempered glass differently. Eventually I found the following:

"Take two photographic polarizing filters.
Sandwich them together. Rotate one of the filters. Light transmitted
through the filters will fade from lighter to completely blacked out as the
planes of the polarized material crosses through each other's axis. Now, try the same thing with the piece of glass sandwiched between the two filters, and rotate one of the filters. If the glass in untempered, the light
transmitted through the filters will act the same way, fading from lighter to
blacked out. If the glass IS tempered, an interesting phenomena will occur: as the filters are rotated, a black cross will form through the filters.
It's an unmistakable sign: if the cross is there, the glass is tempered."

Well, ever heard of this? Anyone ever tried it?

[hobogato]

interesting.

[RNall]

Yes, it is. I do not have the filters unfortunately. I found some relatively cheap on line. I'm sure we could come up with two from the the folks that visit the photography forum though. Do you have any Ace?

It would be simple to go to a LFS and try it out on multiple tanks. If it works it sure would save a lot of people from ruining tanks....

[hobogato]

no, i only have macro lenses and a yellow filter. mark (theotherguy) may have one.

[MattK]

That is absolutely correct with one exception. I just tried it on a tank that I know is not tempered and on the window on my car that I know is tempered. The non-tempered glass had no effect. The tempered glass did, but instead of a black "cross" mine showed black lines.

Pretty cool

[RNall]

I know (from the whole 30 minutes of research I did) that automotive glass is in fact tempured but not to the extent that truly, real, official tempured glas is tempured...really. The air is blown down at 15k psi on official tempered glass and it's only 10k on automotive. The extra 5k changes the tension/compression/blah blah blah significantly. Perhaps this is why it was not a cross???? I'm obviously guessing here.

That's still great news though. There was a difference. I wonder if it's repeatable???? what did you use?

Thanks,

[MattK]

what did you use?

Two Heliopan polarized lenses I have for my camera.

[Bill S]

Look, just use 2 pairs (or one pair if you take one lens out) of cheap polarized sunglasses. $10 at Walmart. Or better yet, 2 pairs of stolen Sea World 3D glasses!

[MattK]

Ok Bill, did you know about this method all along?

[RNall]

Well then, I'm going to try it when I get home (not becasue I stole seaworld glasses though) :D 8)

[MattK]

Keep us posted Ron.

[RNall]

I have 3 sets of polarized glasses (a bit yellow, a bit grey and one a bit blue) There was no change through normal plate glass with any combination. I did NOT notice a change through auto glass with any combination. The glasses have a bit of a reflective coating though. Perhaps that is throwing it off? I do not have a true tempered glasss to check though.

If I could get my hands on decent polarized lenses, I could go to a LFS and make notes... Anyone else want to do something like this - or help me out? If I could definitively say that this works 100%, I could then find a local resource for really cheap polarized glass or film and then we would all have a relatively easy way to check. ((Especially me since I'm in the market for a used glass tank and need to drill holes in it))

Thanks,

Thanks,

[gcantu]

What about some Oakley Polarized Lenses?? Everytime I put mine on, I can see all the cars that have the tempered windshields and windows. Pretty cool, but a pain sometimes...

[urban79]

what about the glasses that are polarized for fishing??

[Bill S]

I didn't know about the polarization of tempered glass - but I DO notice how some car windows look goofy, and of course, LCDs are a pain to see (gas pumps) with polarized glasses. I DID know about putting them 90 degrees - remember that from Physics a LONG time ago, and of course, with my kids (now in college), every 3D thing we went to, I HAD to show it off!

And yes, fishing glasses should work. I'm going to try this in the morning.

[fishcrazy]

If your using it for a sump, I doubt it will matter. Most tank that have tempered glass are only tempered on the bottom and if your using it for a sump I don't think you'll be drilling the bottom, will you?

[RNall]

Well, no. BUT, there are tanks with tempered sides. Marineland tempers their sides....