Klarinet Archive - Posting 000890.txt from 1997/02

From: Roger Shilcock
Subj: Re: glass/crystal (fwd)
Date: Wed, 26 Feb 1997 04:39:57 -0500

---------- Forwarded message ----------
Date: Tue, 25 Feb 1997 12:31:45 -0500
From: Oliver Seely <oliver%DHVX20.CSUDH.EDU@-----.UK>
Subject: Re: glass/crystal

The use of the two terms for me as a chemist is both problematic
and irritating. Problematic because a crystal is a body formed by
an element or compound solidifying so that it is bounded by plane surfaces
symmetrically arranged which reflect a definite internal structure. A
glass is a material not yet in a crystalline state but whose amorphous
structure has been frozen in place by cooling below its softening point.
The use of the word crystal is also irritating to me because it is a bit
of a con. The fourth definition of "crystal" in my old collegiate dictionary
is "glass of superior brilliancy, made into articles for the table, etc."

So unless your mouthpiece was made by chipping away at a piece
of quartz crystal and carved and ground meticulously with carbide and
diamond grinding tools or cast in a mold at its melting point of 1610 deg. C.
it probably isn't crystal, but some form of glass (of superior brilliancy,
OF COURSE, so that the manufacturer can justify charging more for it).
In any case I'd be interested to read the posting of an authority on the
subject
who could tell us what the average melting point is of these various hard and
transparent mouthpieces for which the word "crystal" is bandied about so
casually.

Oliver
Comment: "Crystal" glassware at least is made from glass with a high lead
content and a high refractive index to promote sparkle. Does anyone
know whether this is the case for the material of "crystal" mouthpieces?
Presumably one important desirable property would be lack of "creep"; most
glass
objects change their shape (very) slowly, as glasses are essentially
supercooled liquids.
It would also have to be machineable easily and not so brittkle it
shattered during the process.
Roger Shilcock