Tempered Glass question

[Bryan]

Usually just the bottom, you can generally tell tempered glas as it has a wayy appearance.

http://computer.howstuffworks.com/question508.htm

You can easily spot tempered safety glass in an automobile rear windows on a sunny day if you are wearing polarized sunglasses. Tilt your head 90 degrees or so and you will see a symmetrical pattern in the glass created during its tempering process.