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Re: Tempered Grass Tank (sic)

> Date: Mon, 17 Apr 2000 09:01:03 -0400
> From: "Peter G. Aitken" <peter at pgacon_com>
> Subject: Re: Tempered Grass Tank
> I believe that tempered glass and auto glass are two different things. Auto
> glass is two pieces of glass with a plastic layer between them, to prevent
> the glass from breaking into flying shards in an accident. Tempered glass is
> treated to make it harder and stronger.

Sorry, Peter, but I must disagree here. *Both* are auto glass now. Many
years ago, all glass in autos was laminated "safety glass," -- two thin
sheets of glass with a plastic layer between. It is *much* stronger than
"tempered" glass and still used for windshields, for that reason among
others. All other auto windows are usually tempered.

Tempering is a method of inducing high internal stresses to make the glass
break in a particular way -- typically into small cubes. This avoids the
long spears that regular breaking glass can produce. It is somewhat *less*
strong than either safety glass or regular window glass. It just has a
safer, controlled way of breaking.

Polarized light will not show a single cross, but a waffle-like pattern
where the stress regions are.

This pre-stressing makes tempered glass extra sensitive to scratches. It
takes very little to make the whole window disintegrate. Since gravel
scratches are common in aquaria, I, personally, would not trust (or even
use) a tank that had any tempered glass in it. YMMV.


PS. Don't use a glass cutter on it, if you don't want a big surprise!
Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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