Telescope mirror blank; 8-inch Corning Pyrex borosilicate glass For Sale
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Telescope mirror blank; 8-inch Corning Pyrex borosilicate glass:
$99.95
8-inch Corning Pyrex mirror blank, with rough-ground curve
For your consideration is this vintage 8-inch diameter telescope mirror blank, molded from Corning\'s borosilicate glass oftrade-namePYREX, code 7740. As you may know, Pyrex is no longer available, but is still desirable because of its low thermal expansion coefficient (3.25 x 10-6 per C), which is superior to ordinary plate glass.
This blank has Corning\'s signature tapered diameter and a raised rim on the backside, with the markings \"Pyrex R made in USA\" and \"8D\". These surfaces have a transparent \"fire-polished\" finish, which allow one a clear view inside. By my count, there are 7 tiny bubbles within, all less than 1 mm; final 2 photos try to capture these (but the rough-ground front surface makes them difficult to see).
The front face has been partially processed, and has a rough-ground concave spherical radius of approx 105 inches, extending almost to the edge.There are no chips or fractures; edges have not been machine-chamfered, as they still have the fire-polished rolled edges.
Dimensions:Outside diameter: tapers from 7.99 to 7.75\", front to backThickness (at edge): 1 and 3/8ths inchesWeight: 5 lbs, 0 ounces
Item will be well-packaged for safe delivery; estimated shipping weight is 8 lbs. Local pick-up is allowed.
Compare this offering to the $90.00 list-price of a new molded borosilicate blank from United Lens Co. Mine has the added value (and convenience) of a spherical curve already generated!
Thanks for looking.
