James Avery 925 Sterling Silver Retired Black Onyx Oval Ring Size 6.5 JewelryRing size: 6.5. Signed: 925 James Avery. All gemstone testing in our shop is performed with a Presidium electronic tester. This device identifies whether a stone registers as a. Diamond or diamond-type simulant. Not distinguish between natural, lab-created, or moissanite stones. Because.