how to tell if glass it tempered

Coyle

Coral Samurai
^^ title says it all...i did know at one time, but now that the knowledge would be useful i forgot...i think it had something to do with the clarity or color of the glass when you look through the edge? let me know something, i am interested in a local tank cheap for a sump, and need to drill it.
 
There is no concrete way to tell if a sheet of glass is tempered just by looking at it. There are only two sure ways to know if it's tempered, one is to call the manufacturer of the tank, the other is to try to drill it (if it shatters, it's tempered).

That said, some tempered glass will exhibit an interference pattern in the glass when viewed through polarized sunglasses. To get a look at this pattern, put on some polarized glasses and look at your car windows from outside the car. But just because you can see it in the car windows, this is not to say that your tank glass will exhibit the same thing, even if it's tempered.

HTH,
Kev
 
Aren't all AGA tanks tempered?

I'd like to have mine drilled but the glass shop said fish tanks have tempered glass.

EDIT: I just read another thread and I guess some panes are and some aren't and you should call the manufacture.
 
Look at it through crossed polarizers - tempered glass usually shows a lot of strain bifringence. Get some polaroid material (cheap plastic clip-on shades will work) and view through the glass with one sheet on each side rotated 90 degrees to each other. For instance, clip on one pair to your glasses, hold the other polarizer in front of your light source and rotate it until you get maximum extinction. Now insert the glass in question between the polaroids. Tempered glass will exhibit distinct patterns of dark and light bands or other shapes. You might even get groovy colors. If you can see through the glass edge-on, then it will show a dramatic pattern of colored bands parallel to the faces. If you see no patterns, and light is evenly extinguished as you look through it, then it is not tempered and is pretty well annealed.

Finally, you can examine the glass closely for any brand name etched into it. Examine the edge for any sign of fire polishing. Examine the surface for little dimples where tongs may have indented the glass. Any of these indicate tempering, and you should not try to cut or grind this glass, or you will have a terrible mess.
 
hit it with a hammer.....

...if it shatters into a million little pieces, then its tempered.
...if it cracks into a few big pieces, then its not tempered and safe to drill.

:bum:
 
There really isn't a way to tell with 100% certainty. My theory is, unless you know for sure (checked with manufacturer, etc.), assume it IS tempered.

If the tank is free or cheap enough to take the gamble of drilling, go for it. If you don't want to risk the investment, look for another deal.
 
<a href=showthread.php?s=&postid=6950744#post6950744 target=_blank>Originally posted</a> by gobygoby
hit it with a hammer.....

...if it shatters into a million little pieces, then its tempered.
...if it cracks into a few big pieces, then its not tempered and safe to drill.

:bum:

lol, but i dont think that will help me very much..
 
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