Solitaire Engagement Ring with Milgrained Arches In The Gallery By Scott Kay. Available in 14k gold and 18k gold. The center stone is approximately 0.5 CT to 1.50 CT round shaped, made from natural diamond, lab-created diamond, Moissanite, or cubic zirconia. When you select a natural diamond or a lab created diamond as your center stone you can rest assured that your diamond will look perfect. We use diamond quality standards that are better than the industry average. Your diamond will be at least SI3 or better in terms of clarity, and at least I in terms in color. This means that the diamond you get will look amazing to the unassisted eye, ensuring that you get the best diamond for the best price.