A large, ultralightweight Cer-Vit mirror of oblong shape has been optically polished to a surface irregularity of 0.060 rms, where = 0.633 urn. Although its major dimension is 193 cm, its finished weight is only 97 kg. The nonconventional fabrication methods required by its light weight, unusual aperture shape, relatively steep curvature, and excep tionally large diameter-to-thickness ratio are described. A 64-point fluid piston mount employed to support the mirror both for optical fabrication and for interferometric test ing is also described. Techniques specially developed to produce both the mirror blank and the final optical surface demonstrate significant advances in the manufacture of large, very lightweight glassy mirrors of high optical quality.