Optical tests were made on six paraboloidal metal electroplated replica mirrors of 3″ diameter and 2″ focal length, produced from convex glass masters. It was shown that the better replicas reproduced the features of the master surfaces with an average error of 5 or 6 microns per cm along the surface. Three of the replicas gave noticeably distorted images of a point source because of warping, introduced presumably in after electroplating. the process of separating them from the masters after electroplating.
JOHN N. SHIVE, "Investigation of the Figure of Small Concave Metal-Replica Mirrors," J. Opt. Soc. Am. 37, 849-849 (1947)