by vapor deposition although other techniques such as spinning may be used to provide the very uniform film that is required then a thin protective film 7 of aluminum for example is applied by vapor deposition over the release coat 6 if needed a thin film of gold may serve as a release and a second film omitted on the coat 6 7 of one support 2 is poured a bead 8 of liquid transparent epoxy compound a suitable compound is a 10 to 1 viscous mixture of an epoxy resin with terminal epoxide groups and a liquid polyamine curing agent the prepared face 3 of the other support 1 is then pressed down by its own weight or otherwise face to face over the epoxy compound spreading the epoxy so as to shape a shield disc layer 8 fig3 to 6 uniformly a few thousandths of an inch thick e g 0 001 to 0 005 the epoxy shield is then allowed to cure when the epoxy shield is cured the upper blank support 1 is lifted off the shield parting at the upper release layer 6 leaving a film 7 of aluminum over the epoxy shield 8 fig4 preferably an annular area around the periphery of the circular shield is cleaned of its exposed aluminum film by abrasion or by a solution of sodium hydroxide and water in the proportion of one cup to five gallons of water a frame or holder comprising a ring 9 of at least the peripheral dimension diameter of the shield is then adhered with epoxy cement to the cleaned peripheral area of the epoxy shield fig4 preferably while it is still on the lower blank support 2 the ring may be aluminum or other material.