A hint of color is all you need with this example of a period Art Deco ring. Open work filigree of 18k white gold will cause stars in your eyes with an old European cut diamond of an estimated .42 carats (H-I color; VS2-SI1 clarity) set in a lozenge shape bezel giving the diamond a visual look of having a greater carat size than its actual weight.
Flanking the centered diamond are two (2) triangular shaped synthetic emeralds. Diamonds were the main focus of that period of jewelry with synthetic colored gems used for contrast. Please note the incised design along the shank.