It is possible to change the figure of reflecting surfaces quantitatively by controlled deposition of metals, evaporated in vacuum. The theory for calculating screens and the experimental technique are described. A spherical 12-inch mirror has been repeatedly parabolized, obtaining a surface perfect within 0.05 wave-length. A 5⅝-inch spherical mirror has been parabolized with the optical axis outside of its periphery. A defective parabolic mirror was corrected for turned up and down edges. A convex spherical secondary mirror was hyperbolized. The limitations and possible applications of the method are discussed.
JOHN STRONG and E. GAVIOLA, "On the Figuring and Correcting of Mirrors by Controlled Deposition of Aluminum," J. Opt. Soc. Am. 26, 153-153 (1936)