Process for making a die punch

A process for making a concave die or die punch of the type required in the formation of highly specific silicone elastomer contact lenses of negative power of refraction in which the curvature of the marginal zone must be greater than the curvature of the central zone,

• the said process comprising
• a. making a convex die negative of desired differential curvature from glass or a vitreous ceramic;
• b. providing the negative with a metal coating of a thinness to permit it fully to conform to the surface curvatures of the die negative;
• c. placing a concave die positive consisting of a heat hardenable resin in uncured condition in an open top mold;
• and
• d. introducing the die negative into the mold and bringing the said metal coated surface of the die negative within the constrained spaced of the mold into close contact with the die positive while heating the said resin to harden it, thereby causing the metal coating to become detached from the die negative and to adhere to the die positive, thus transferring the metal coating to the die positive so that the surface of the die negative is reproduced on the die positive.