GB798080A - Imitation gems consisting of glass, transparent plastics or the like - Google Patents

Abstract

798,080. Imitation gems. SIMILI FABRIK FEINER SCHLEIFPRODUKTE ANSTALT. Sept. 20, 1955 [Sept. 29, 1954], No. 26872/55. Class 43 An imitation gem of glass, transparent plastics or the like has the rear portion 5, which is adapted to be located within a setting 17, provided with a continuous coating 6 of a material which reflects a portion of the light that is incident upon it and allows the remaining, preferably smaller, portion to be transmitted through it. In the example the gem is formed with a front face 2, facets 3, peripheral edge 4, and a facetted pointed lower part 5 which is coated with a semi-transparent layer of silver 6. Part of a light ray 7 which impinges on a facet of the lower part 5 is reflected along the lines 10, 13 and 16, whilst part is transmitted through the coating in the directions 11 and 14 and, upon casual examination, gives the effect of a genuine stone. Preferably the coating consists of a thin, highly reflecting layer of a metal such as silver, chromium, rhodium, or a metal compound such as an oxide, sulphide or fluoride, deposited for example by evaporation in a high vacuum, by cathode sputtering or by a chemical or physical centrifugal process. The coating may comprise a succession of several thin layers of the material, the optical thickness of the individual layers preferably being equal to one-quarter of the wavelength of the incident light or a multiple thereof. A transparent protective layer, e.g. of silicon dioxide is preferably applied over the semi-transparent coating material, the thickness of such protective layer preferably being equal to, or a multiple of, half the wavelength of the incident light. The setting 17, which holds the gem above the peripheral edge 4, is open at its lower portion 18, so that the light rays 11 or 14 are received by a viewer looking at the gem from below.