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Gemini No. 1 Primary Mirror Blank Successfully Slumped (1Jun95)
(from NOAO HIGHLIGHTS!, NOAO Newsletter No. 42, June 1995)

On 28 February at Corning's Canton, New York facility, the Gemini No. 1
primary mirror blank was heated to more than 1400d C and successfully
slumped over a refractory form to give the blank its final meniscus shape. The
blank, now dished approximately 29 cm (11.4") from edge to center, was
cooled at a controlled rate over the following four days for proper annealing.

The convex surface has since been generated to final shape, the blank turned
over, and now the concave surface is being generated to shape in preparation
for final grinding and polishing. Finally, the outside diameter and central hole
will be ground to final dimensions. All surfaces except the concave surface
will also receive an acid etch treatment to increase strength and durability of
the blank.

The No. 1 blank will be completed at Corning by mid-November, 1995 and
then transported to REOSC Optique near Paris, France for grinding and
polishing of the optical surface. Work is progressing smoothly towards a
December 1995 fusing of blank No. 2.

                           [Photos not included]

        The blank being lifted into place on the refractory form.

        The blank rests on a 1 meter diameter contact point of the refractory
        form prior to slumping. The furnace is seen in the background.

        The successfully slumped blank showing the minor fire polishing
        caused by the furnace jets near the rotating surface of the blank.

        The blank in its final meniscus shape is ready for generation.

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