Re: ATM Info on plate glass.... what is it actually ??

[Kurt Hillig <khillig@umich.edu>]

On Wed, 17 Sep 1997, Gerald Hubacek, studmail, FB02 wrote:

>       :       :       :       :       :       :       :       :
> I am wondering what plate glass really is.  I have asked around in 
> Iceland and nobody seemes to know this name.  Is it just normal glass 
> used in windows or something else ???
>       :       :       :       :       :       :       :       :

Plate glass and window glass are the same stuff, with small variations
depending on who makes it.  But both are basically "soda-lime"  glass - a
blend of silica (silicon dioxide), sodium oxide (from soda - sodium
carbonate), and calcium oxide (lime).  It's generally distinguishable by
having a faint green color, most noticable when you look at the edge of a
piece.

Pyrex and related glasses are "borosilicate" glasses, which have boron
oxide in the mix as well.  Other optical glasses include such compounds as
barium oxide, zirconium oxide, various metal fluorides, etc.  These are
generally much less strongly colored than plate glass. 

Tempered glass is generally soda-lime glass that's been through a heat
treatment to put the surface under a strong compressive strain; this makes
it fracture into small, roughly square, fragments rather than long sharp
needles when it breaks - great from  safety standpoint - but also makes it
almost impossible to grind without shattering.

Laminated glass consists of (typically) two layers of glass (often
tempered) with a thin adhesive plastic layer in between, to keep the
pieces from flying when it shatters under impact.  This is also pretty
much useless for optical work.

                            Dr. Kurt Hillig
  UMNet Administration     I always tell the    fax (313)763-2180
 University of Michigan     absolute truth     phone (313)647-8778
Ann Arbor, MI  48109-3297    as I see it.    X.500 khillig@umich.edu

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