Un-silvered mirrors

A solar concentrator with prismatic reflectors. Rabl & Rabl US4120565.

In making an all-glass solar furnace it would be desirable to avoid the use of silvered or aluminized mirrors. The use of prismatic reflectors, is a possibility for telescopic heliostats. The primary mirror tracks the sun precisely in azimuth, and the secondary mirror sees a stationary light source of only 3° divergence. Both of these situation are ideal for prismatic reflectors...

...on second thought, I don't think this can work. The optics of these surfaces depend on the dihedral line rather than the surface normal. For example, in the image of the trough concentrator above, if the prisms ran in the longitudinal direction there would be no concentration because there would be no curvature of the dihedral lines. This technique seems to need radial symmetry to form an image.