vycor glass is manufactured exclusively by Corning as an alterntive
to Quartz (pure SiO2). Specs are:

VYCOR -
common name: High temperature glass
SiO2 96.4%, 3.0% B2O3, 0.5% Al2O3
Strain Point 890 degrees C
Anneal Point 1020 degree C
Soften Point 1530 degree C

Quartz -
SiO2 99.9%
Strain Point 1050 degrees C
Anneal Point 1210 degree C
Soften Point 1650 degree C

PYREX - (Corning 7740)
common name: Borosilicate glass Type I glass
SiO2 80.6%, 13.0% B2O3, 4.0% Na2O, 2.3% Al2O3
Strain Point 510 degrees C
Anneal Point 560 degree C
Soften Point 821 degree C

Hope this helps. Information on Pyrex and Vycor is from the
Corning Labware and Equipment Catalog 97/98.

Rick


A. Richard Heemskerk               [log in to unmask]
Environmental Isotope Laboratory   Telephone: 519-888-4567
Department of Earth Sciences       Extension: 5838
University of Waterloo             Facsimile: 519-746-0183
Waterloo, Ontario, Canada N2L 3G1  http://sciborg.uwaterloo.ca/~rkhmskrk