8-inch telescope mirror blank; PYREX borosilicate glass For Sale
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8-inch telescope mirror blank; PYREX borosilicate glass:
$95.95
8-inch United Lens Co Pyrex mirror blank, with curve
For your consideration is this vintage 8-inch diameter telescope mirror blank, molded by United Lens Co from Corning's PYREX borosilicate glass.
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.
The blank has been partially processed; one surface (rear) is fine-ground nominally flat, and the other (front) has a medium-ground concave spherical radius of approx 56". The perimeter has the original molded finish, with a couple of stoned cavities (repair of chips; see pic #2, 3 and 4) at the rear edge (NO encroachment into the front aperture). The front edge has a modest chamfer, free of chips; the rear has a generous but rough chamfer.
Wetting the rear surface and edge-lighting allows one to see inside (see final pic); I see no bubbles of any significance!
Dimensions:Outside diameter: 8.025"Thickness (edge): 1.30"Weight: 4 lbs, 15 oz
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. Mine has the added value (and convenience) of a spherical curve already generated!
Thanks for looking.