This mirror is in excellent condition. Using an infinity collimator the focal length was determined to be almost exactly 12 inches, yielding a radius of curvature of 24 inches. The glass is 1.375 inches thick at the margins.
We don't know too much about the characteristics of the item, but it was in with several pieces of fine glass that were manufactured by ITEK, who used to be the premier lens designers for the military, most notably the National Security Agency's ultra-high resolution spy satellites.
This mirror appears to have some sort of dielectric coating over a solid reflecting substrate (Al ?). There are no markings on the mirror, and the finish appears to be essentially free of flaws, although there are some motes of dust on the surface.
Photo set 1677