What is glass made out of and is it porous? The reason I ask this is
that I am an Enjo consultant and I recently had a customer asking that
question.  I was under the impression that glass is porous and is made
out of sand and water.

garbs-ga:

Actually, glass can be made from a wide range of materials, although
the primary material is usually silica (sand). For more information
than you would ever want to know about glass, please visit this
website hosted by the Corning Museum of Glass:
 

A RESOURCE ON GLASS
Art, History, Science, Literature, Social Studies, Technology
http://www.cmog.org/page.cfm?page=77

Your question is best answered by reading this article:

SIMPLE GLASS MAKING 
http://www.cmog.org/page.cfm?page=283

- primary components of 'simple' glass are crushed white sand, crushed
limestone, and sodium carbonate


As for glass being porous, in its normal state it is not porous.
However, as documented in the following page from the Corning Museum
of Glass, under certain chemical conditions glass can be attacked by
an acid solution, rendering the surface porous:

-----
Properties Of Glass: Chemical
http://www.cmog.org/page.cfm?page=316

"Acid corrosion behaves quite differently. By dissolving the alkali in
the glass composition, a porous surface is left that consists of the
silica network with holes where the alkali has been removed by the
acid. This porous surface slows the rate of attack since the acid must
penetrate this surface layer to find alkali to dissolve.

Corrosion by water is similar to acid corrosion in that alkali is
removed from the glass surface. Water corrosion acts at a much slower
rate. At high temperatures, however, water corrosion can become
significant. Gauge glasses for steam boilers are a case in point.
These products must be protected from the superheated water by a sheet
of mica or replaced on a schedule that insures that they will not be
seriously weakened."
-----

So, to summarize, glass is primarily made of crushed white sand
(silica), crushed limestone, and sodium carbonate. When exposed to an
acid solution, a glass surface will eventually become porous; however,
the rate at which this occurs depends greatly on the acidity of the
solution and the temperature.


I hope this helps!

aht-ga
Google Answers Researcher

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Request for Answer Clarification by garbs-ga on 21 Apr 2004 17:01 PDT

Is glass porous though?

---

Clarification of Answer by aht-ga on 21 Apr 2004 18:04 PDT

In its normal state, glass is not porous, according to the "Properties
of Glass: Chemical" link I provided above.

I hope this helps,

aht-ga
Google Answers Researcher

Thanks for your help with this one