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[Joe-Ceph]

oh, lol ok. Thanks for telling me that! Maybe I'll make one out of plexi then..

You can drill grind or cut regular glass, but not tempered glass, so find out which you are dealing with by doing the test with an LCD screen and a polarizing filter. It's highly unlikely that the sides of any aquarium are made of tempered glass, so I recommend that you do the test before you abandon the idea of drilling.

In general, when you put a piece of tempered glass between two polarizing filters (like polarized sunglasses), you can see how the tempering changes the way light travels through the glass (you'll see colors and patterns that are invisible when there is nothing, or non-tempered glass, between the two polarizing filters.) The glass on most (all?) LCD screens is polarized, which is why the test above works, but you can also to it with two pairs of polarized sunglasses (or one pair if you can separate the lenses). The glass used for refrigerator shelves is always tempered, so you can use that as a baseline to get an idea of what tempered glass should look like between your polarized filters.

For the science nerds:
Tempering shrinks the inside of the glass relative to the outside. The outside surface is compressed, causing micro cracks and imperfections in the surface to be closed, making it harder for a crack to start. This also means that the density of the outside of the glass is a little different (less) from the density of the inside. Light travels through the denser parts a little faster than the softer parts, they also have a different index of refraction (this is called birefringence). This difference manifests as different colors, when polarizing filters are used to filter out the noise. Heat tempering is done on metal rollers, and the parts of the glass touching the rollers heats and cools at a different rate than the other parts of the glass, resulting in the checker-board pattern you sometimes see when looking at car windows through polarized sunglasses.

 

[DWhatley]

I just had a tempered glass door fall from its support hinges in the middle of the night. Talk about a mess! There were thousands of small pieces.

I think Joe-Ceph's point is though that you are very likely to be able to drill the sides of any of today's tanks but if you want a bottom drill, the chances of it being tempered increase greatly. Certainly the test (and baseline experiment) are well worth the time.

I did some forum surfing on the topic of tempered sides and found both a reference to Joe-Ceph's polarizing test and to an individual that drilled one that had tempered sides (start at post 6).

Mine was. It fit into a small trash bag when I was done sweeping it up

The topic brings up an interesting thought. With the octos ability to see polarized light, I wonder if tempered sides would effect them.