This work focused on the fabrication of an ultralightweight honeycomb sandwich mirror substrate 30 cm in diameter, of 96% fused silica glass. The technique used was the gas pressure inflation method developed at Steward Observatory's Mirror Lab at the University of Arizona. The method was first developed with borosilicate glass that fuses at 850 degrees C. The new mirror is of Corning's Vycor glass which has much lower thermal expansion and fuses at 1600 degrees C. In order to use this glass we have had to find new refractory materials compatible with the process. In particular, we have had to control outgassing and chemical interaction between the glass and the mold. The techniques developed should now be applicable to refractory glasses with zero expansion coefficient. The density of the present blank is kg/m**2. Densities as low as 20kg/m**2 should be readily accomplished. This work is supported by NASA under grants NAGW-121 and Ames NAG-161.