(ATM) Re: Fused silica properties??

[epabcc@epa.ericsson.se (Bratislav Curcic)]

Measure the specific gravity of the blank (digital scales
and "water displacement" method), and look at some good tables
(i.e. Schott catalogue and such). There will be very few (none?)
of the glasses with the same specific gravity as fused silica,
and there is fair chance that those glasses won't be as clear
as silica. In other words, if specific gravity matches, glass is
clear and hard (much harder than crown), you've got real fused 
silica. Otherwise, it's probably Pyrex/Duran (still excellent for
a 6").

Bratislav