Vintage Ametrine Gemstone Sterling Silver Ring

Large bi-color oval faceted ametrine gemstone in purple and yellow. Prong set in sterling silver. • Gem measures 16 long x 11 wide x 10 high mm • Stamped sterling on inner band • Maker's hallmark on inner band • Vintage 20+ years • Four prong setting • Ring size US 5 1/2 Excellent condition. I could not make out the maker's mark. I tested the gemstone with the Presidium Gem Tester II. HD5