PYREX® BLANKS

FINE ANNEALED BLANKS FOR AMATEUR TELESCOPE MAKERS (ATMs). Blanks are borosilicate glass disks, extracted from a plate of Corning Pyrex® 7740 (equal to Duran® 50) with a low coefficient of thermal expansion (3.3x10-6/°C) while the standard glass (sodic calcium ) has got 8.5x10-6/°C. Pyrex® blanks from plates got better glass homogeneity and less presence of bubbles and inclusions in the material, compared with n ormal glass or Pyrex® disks moulded directly from the melting glass.

The raw glass disk is first levelled and then its edge is grinded down, to get a curve edge surface perpendicular to flat faces. To obtain blanks with a concave surface, we first give it a spherical shape with the requested radius; the blank is then treated for fine annealing process that lasts 72 to 120 hours, depending on disk diameter and thickness. All stresses coming from the fast cooling of the vitreous cast mass are removed; the blank optical surface is then flattened again and roughly shaped to the requested concave surface. The blank is now ready for next glossing phases.

The price of our own production blanks includes the packaging cost; here's a typical packaging of a 510mm Pyrex blank.

Packaging of three 40" (1013mm) Pyrex disks