how to tell if tanks tempered

[gcantu]

If you can get a hold of some 'Polarized' sunglasses, put them on and look at the tank. if the glass looks wierd, then it is tempered. By wierd, I mean, if you can see blurry squares or dots within the glass then you are out of luck. That's another easy way...

[tiggamonsta]

How do they make tempered glass?

There is an explanation on the link below. Basically it is heated and then cooled rapidly.

http://www.crystallineimages.com/HT_temp.htm