A method for manufacturing a mirror blank comprises: providing a primary piece of glass comprising a primary planar surface and a backing piece of glass comprising a backing planar surface; assembling a mirror blank assembly, wherein assembling the mirror blank assembly comprises interposing a plurality of glass splines between the primary glass and the backing glass. Interposing the plurality of glass splines comprises: for each glass spline, respectively abutting first and second opposed surfaces of the glass spline against the primary planar surface of the primary glass and against the backing planar surface of the backing glass. The mirror blank assembly is then heated to fuse the interposed glass splines to the primary glass and the backing glass while the primary glass and the secondary glass remain spaced apart from one another by the interposed glass splines to thereby provide the mirror blank.