Simulated Opal Ring This handmade ring features a 4mm Simulated Opal stone, bezel mounted on a skinny 1mm wide 14K Gold Filled Plain band. Polishing cloth and ring sizer included. Shipped in gift box. Opal is the birthstone for October. Gold filled "14/20" refers to the industry shorthand describing the resulting material. The first number is the karat purity of the gold used; the second number is the amount, by weight, of gold to the substrate material. "14/20" gold-filled material is made with 14-karat gold and the gold represents 1/20th (or 5%) of the total weight of the material.