[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [APD] Glass myths

Well that means my local glass shop lied to me. Which figures. Cause I 
called and specifically asked for plate glass. Is it possible the 
moniker has just taken new meaning? Perhaps when you ask for plate glass 
your now asking for Float or Sheet? It wasnt very expensive.

Wright Huntley wrote:

>There has been a great deal of what sounds like misinformation about 
>glasses here, lately.
>First, can someone cite any reference that tempered glass is stronger 
>than ordinary sheet glass? It was stated as fact several times, without 
>IMHO, it may be slightly stronger in some applications, but it usually 
>isn't a great deal stronger. Its advantage is the way it breaks without 
>leaving large slicing pieces. It has a deliberately built-in stress 
>pattern that causes the little cubes to form when it shatters. That 
>makes it far weaker than other glass when scratched, BTW. Really dumb to 
>use in any aquarium where gravel can accidentally scratch and shatter it 
>during cleaning. Good idea for terrariums, maybe (except for cobras?). I 
>don't even like it in the bottom glass, but shower-door material is too 
>common and available in those thicker sizes, so they do use it in larger 
>tanks. The bottom is less likely to get scratched during cleaning, anyway.
>It isn't a bit lighter than the same thickness of sheet glass of the 
>same chemical formulation. It normally is still just single-thickness 
>soda-lime glass with a built-in stress pattern. [Of course the glass can 
>be chemically formulated to be stronger, but IME it usually isn't.That 
>has nothing to do with the tempering.] Look at it between crossed 
>polarizers if you want to see the pattern. You can often see it in car 
>side and back windows when you are just wearing Polaroid sunglasses, if 
>the sunlight is at a low enough angle to be polarized a bit.
>Most aquariums are made of sheet or float glass. Plate glass disappeared 
>many many years ago as it was way too expensive and labor intensive. 
>They quit making it here in the US, before most of you were born. Float 
>glass was getting just too good to distinguish them, but was far 
>cheaper. There is no such thing as plate glass in the American consumer 
>market. It is imported for some fancy mirrors, coffee tables, etc. but 
>not for windows or aquariums. There is not, and hasn't been, since about 
>the '50s, any major American maker of plate glass. Plate glass is 
>regular window glass that has a final step where it is ground flat and 
>parallel, and then polished like fine optics. Expen$ive!
>Water-white glass is not just "low iron" glass. Basically, it is the 
>same as the brand-named "Pyrex" in that it has higher purity and 
>higher-temperature fluxing agents. It is also often formulated to have a 
>lower thermal expansion coefficient (more soda, less lime?), so it 
>doesn't break from quick heat changes. It has to be handled at higher 
>temperatures so is more expensive for most applications. It usually is 
>stress relieved (annealed), so tends to be very strong, too. Still 
>glass, it is made by casting (float) or drawing (sheet), like other 
>glasses. You can spot it instantly as the edges do not look green.
>Tempered glass is very different from laminated safety glass. The latter 
>is used in windshields mostly to keep you in the car in a collision, and 
>(perhaps) avoid the blinding if tempered and it didn't all fall out when 
>hit by a pebble. It also doesn't cause polarized "rainbows." It is two 
>thin sheets of glass bonded to a plastic center layer. You cannot, as a 
>practical matter, usually cut either safety or tempered glass at home. 
>Most auto glass is tempered, after the outline and curvature are 
>established, as a final step. Safety glass is usually annealed to 
>relieve all stresses, make it stronger, and to avoid the polarization 
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com