Momentive Quartz Material:
Momentive Performance Materials (formally GE Quartz) is a key supplier for quartz material used at Glas Werk Inc.

Heraeus Quarzglas:
Heraeus Quartz Materials is a key supplier for quartz ware material used at Glas Werk Inc.

or product of equivalence:
Glas Werk, Inc.  works with a variety of quartz material suppliers to meet your particular needs.