This report covers an investigation for electroforming metal trihedral prisms with reflecting surfaces that approach the optical accuracy of commercial trihedral glass prisms and the field testing of the metal prisms in comparison with the glass prisms. The optical response of the best of the metal retro-directive reflectors at a distance of one mile was about three-fifths that of a commercially produced glass prism having an optically active area about three times greater than the area of the metal prism. The report concludes that the metal prism, although about as accurate as a commercially produced glass prism at a distance of one mile, is still not as accurate as its mold. However, continued improvement in the optical accuracy of the successively manufactured metal prisms indicates that the ultimate optical accuracy possible by the electroforming process has not yet been determined. Metal retro-directive reflectors produced by electroformi would cost about one-sixth as much as a commercially produced glass prism of the same optical accuracy.
BENJAMIN GOLDBERG, "Electroformed Precision Prisms," J. Opt. Soc. Am. 38, 409-409 (1948)